How Plant Growth is Limited (container forum version)

tapla (mid-MI z5b-6a)September 19, 2010

In a recent post, I suffered criticism after I tried to explain why light could not make up for or 'trump' the negative affects of other factors that potentially limit plant growth. Liebig's Law of the Minimum is a universally accepted concept that defines how the growth of plants is limited. Originally the law was viewed by Justus Von Liebig, a German chemist who is often referred to as 'the father of the fertilizer industry', as a fitting way to define the fact that plant growth is not limited by the total of the available resources, but rather, by the single resource in shortest supply.

Though Liebig's focus at the time was on nutrition, his concept was later expanded to include other limiting factors as they were discovered. Not only are each of the elements commonly regarded as essential to plant growth recognized as having the potential to individually limit growth, but the law has also been expanded to recognize the limiting effects of cultural conditions like light, temperature, levels of soil moisture and aeration, insects, disease, and others.

Liebig used a barrel with staves of varied heights, like you see in the picture, to illustrate how his concept worked. Imagine the barrel also had a stave for light, soil moisture/aeration, temperature ..... for each and every potential limiting factor, insects and diseases included. The picture above is illustrating that in this case, N is the limiting factor. The plant is not growing as well as it could be because it is N deficient. When we add more N, and N is no longer the nutrient or potentially limiting factor in shortest supply, something else takes its place as the limiting factor. Even if the supply of N was increased to the point where it was in perfect supply, the least available nutrient or cultural condition would STILL be the limiting factor. We raise the stave representing N, but then another stave representing another resource becomes limiting.

You can see that if light levels are made perfect, it wouldn't compensate for the effects of a N deficiency or a soggy soil. If it could, we would be able to grow our plants in peat porridge with no supplemental fertilization at 32* F in a wind tunnel .... as long as it was a bright wind tunnel .... or we focused on perfecting light levels. The same is true of soils. The most perfect soil we are able to build will not make up for or 'trump' the effects of a nutritional deficiency or poor light.

Our goal then, is to try our best to make sure ALL the cultural conditions are optimum - making ALL the staves taller, as it were. It doesn't do us any good to make all but one stave taller, because it is that pesky short stave that is going to limit growth - EVERY SINGLE TIME! Surprisingly, it is not as difficult as it sounds.

Light and temperature are actually very easy. The onus of learning your plants' preferences for these cultural conditions is on you, but they are very easy to learn and easy to correct, so that issue needs no more attention. Insects and diseases might be a little tougher, but IPM practices are derived from common sense. Identify the pest/disease and use the least noxious remedy possible to reduce the problem to something below your tolerance threshold.

Modern fertilizers make it easy to supply nutrients at near optimum levels and in a ratio to each other that is favorable. Tucked into Liebig's Law is the fact that too much is as bad as not enough, so there is incentive for us not to cater to the idea that because a little is good, more is better. As we look at the barrel example, we can see that increasing the N supply so the N stave is taller than the P or K staves is not going to help. So, using fertilizers with a favorable ratio and applying them wisely is actually something we can all manage.

Because this is the Container Gardening Forum, the most frequent source of trouble and the issues that arise with the most frequency are soil related. Soil moisture and aeration are staves as critical as any other in the barrel. Just as a perfect soil cannot 'trump' the effects of other short staves, optimizing other conditions cannot offset or 'trump' the effects of a poor soil. The necessity of making sure your plants are adequately supplied with water is an obvious given. The effects of excessive water retention and inadequate aeration are widely discussed on the forum. You can learn how to avoid these issues entirely or almost entirely by reading about How Water Behaves in Container Media by clicking this highlighted text; or you can read some tips about

How to Deal With Water-retentive Soils by clicking on this highlighted text.

Keep learning. The more you know about how your plants grow, what cultural conditions they prefer, and the effects varying cultural conditions will have on your plants, the better equipped you are to deal with them, keeping all the staves tall and minimizing limiting effects.


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haase(10 CA)

What a great, informative lecture. Thank you, Al.

    Bookmark   September 19, 2010 at 9:52PM
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jojosplants(9/ Tucson, Az.)

What a great post!
The barrel really helps pull it all together.
I'm sure many will find this as useful as I do.
Myself, and i'm sure many here appreciate all the time you put into these posts so that we, and our plants can be happy.

    Bookmark   September 20, 2010 at 10:29AM
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suddensam(10 Boynton Beach)

Some of your best work sir. If you grow in containers which im sure the people reading this do its a must read. I have forwarded this to several of my friends that call me and ask questions, as im sure this helps with a lot of problems. Thanks for your time and effort.
Plant em if you got em.

    Bookmark   September 20, 2010 at 10:57AM
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After spending many hours reading these forums and being amazed at the amount of information and dedication from Al and others, I have switched to Al's mixes with great success, but had not been able to find the elusive FP. This weekend while visiting Santa Rosa, CA, I called around and the nice people at New Harvest Hydroponics, 807 Washington Ave., Calistoga, CA. brought some in for me. If anyone in that area of the country is looking for it, they have it in stock now. Our "other Al" from Calistoga probably knows those folks? A beautiful town to visit, too!


    Bookmark   September 20, 2010 at 12:01PM
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Beacaue of informative articles like this, or should I say FREE sermons that I would pay for at my local Bonsai store, I have been able to keep all the "staves" taller..Well sort of on the light one..

I also realize that many plants can not be grown in certain types of soil, no matter how much light you give them, such as Orchards, Violets, Succulents, Cactus. Exotics, and etc..

The wrong soil mix has never been as forgiving as the pest's, light levels, or fertilizers which can be adjusted rather easily at any time..I find I can loose a plant as quick as lightning if any plant sits in muky soil, longer than a few days, especially in winter.
By the time I realized the plants demise, it was usually to late..

I have been able to find a way to make all my plants happy and make a few mistakes with other essentials, but the mix, for me, that is not as forgiving unless you get that just right the first time...

Al, from the bottom of my heart, thank you for helping me to be able to keep my plants alive and understand all these concepts, every one of them, including rare and unique tropicals, succulents, cactus, jades, citrus, plumerias and many more that a majority of the people can not unless they have a greenhouse on their side or huge south facing windows for sun loving plants..Also for the plants that require low light and dark corners, growing in the mixes introduced my you has also made it possible, even without the gnats..;-)

I only have a couple of begonias to move over to the 5.1.1 mix since the mix they are in is as hard as brick now. I bought them 4 months ago in regular potting mix..

Al>>>>>>>>> Because they are in 4 inch pots and the mix is so hard, which leads me to believe I am not going to be able to remove amy of it unless I break many roots, what do you suggest?


    Bookmark   September 20, 2010 at 1:03PM
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jojosplants(9/ Tucson, Az.)

Not wait so long next time. ;)

Actually, I have a tree and strawberries in the same situation.. But ive only had the a few weeks! They came that way..UGH!

I have a very busy week ahead of me, switching MANY plants over to the mixes. ;)


    Bookmark   September 20, 2010 at 1:28PM
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You know what that's like..We just say, when I get around to it when we are extra

I usually repot as soon as they come home, but for some reason, these got neglected..I am waiting for them to croak just like that by the time a have a moment to to

Sent you an e-mail by the way..:-0)


    Bookmark   September 20, 2010 at 1:36PM
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tapla (mid-MI z5b-6a)

Thank you so much for the very kind comments, everyone. I'm so glad you found it helpful.

Mike - As JJ knows from the times she's asked similar questions, I would lean heavily toward, and without hesitation ..... just bite the bullet. Prune the roots AND top back hard, remove all the old soil, and repot it in fresh soil and wait for it to back-bud like crazzy.


    Bookmark   September 20, 2010 at 2:13PM
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Ok....Will do..

I am a bit scared with this one..It is one of my favorites and seems quite happy for the moment with big leaves, but as we know, not for long...
Bite the bullet it is, or take the bull by the

So I am going to post a picture of it here as soon as tomorrow since I will have a few moments ,
and what I do with your help, and we will go from there..
This is a first for me cutting roots and plant as so..

Let me post a picture first and you tell me where I should cut the top from... Thank you for your great support!


    Bookmark   September 20, 2010 at 2:44PM
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This is the Begonia, and as you can see, the leaves are growing from the top of the soil.Just big long leaves..The mix is very hard and the roots do not look healthy to me already..

Do I cut all the leaves off? There is no trunk or stems, just long leaves..

Thank you..:-0)

    Bookmark   September 21, 2010 at 1:07PM
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tapla (mid-MI z5b-6a)

The roots don't look that bad to me, Mike. Why not pot up into the 5:1:1 mix and wait until s spring to repot?

If you do repot now, remove all the soil & use your judgement as to how much of the top the roots will support. Then, remove oldest foliage first until you think the roots and top are somewhat balanced. I only advised that you do it this way because the plant is going to shed a portion of the foliage when you remove a lot of rootage. if you don't remove it. Technically, the plant will recover faster if you just do the root work and repot w/o cutting back the top, but you'll have a really ugly plant (because of the dieback) while you wait.


    Bookmark   September 21, 2010 at 2:01PM
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puglvr1(9b central FL)

What a great post Al...Thank you for taking the time to post this very helpful information. I know many of us here truly appreciate the time you put into helping so many of us.

Mike that is a pretty begonia...good luck with them!

    Bookmark   September 21, 2010 at 9:23PM
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tapla (mid-MI z5b-6a)

Awww - thanks, Nance. ;o)


    Bookmark   September 21, 2010 at 9:32PM
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Thank you Pug for noticing how nice the plant is..
I love it, especially in bloom..It seems to be the only plant that loves the bathroom window..:-)
How is your baby adjusting?:-)

I did as you suggested and potted up into a bigger pot with the 5.1.1 and will wait till srping per your first suggestion. I can always count on you too tp help me do what is best for my plants..Thank you.

I will address this come spring..:-)


    Bookmark   September 22, 2010 at 1:26PM
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One more thought,

I was thinking of all the myths many have on plants and I can name you another problem that can limit growth on many plants despite what many think....

Keeping plants in tight pots...Many have different reasons why they like to keep plants in tight pots, while many actually believe that the bigger the pot the more the plant will concetrate it's energy on root growth and not push out growth on top..

What do you think anyone? Al, could you expound on this?

To me, it only makes sense that if all roots have free reign to roam in the ground with no borders, then it only makes sense that free reign to roam in a container would actually encourage better growth on top too...Just a thought.
For instance, my citrus trees planted in the ground, grow several feet higher than those in containers within the same year?
Put a Red Tail Sword fish in a 30 gallon tank, they only grow about 6 inched at best. Put one in a 100 gallon tank, they can grow as long as a foot!

That is why it is so important to use a mix that allows one to put plants in much bigger pots for phenominal growth and not have to worry about rot or PWT problems.....


    Bookmark   September 22, 2010 at 1:49PM
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tapla (mid-MI z5b-6a)

Something I wrote a while back:

Myth: This Plant Likes/Prefers to be Root-boundsize>color>

I would like to talk a little about, and hopefully dispel the myth that certain plants 'like' or 'prefer' to be grown tight (under root-bound conditions). Maybe we can also understand that no plant will 'do well' when it's pot-bound if you are using a plant with plenty of room for its roots as your standard of judgment. If plants did better growing under root-bound conditions, it would seem that Mother Nature would have arranged for in situ (where they naturally occur) plants to grow with their roots in tight little cones or cubes, yet we never see that occur. While it's true that we may be able to use the STRESS of our plants being root-bound to bend plants to our will and achieve OUR goals, the fact is that this serves US well, and not the plant.

Lets examine what 'growth' is. Growth is simply a measure of the increase in a plant's biomass, how much bigger it has become (the weight of the sum of it's parts), and is the actual measure of how 'well' a plant is doing. We know that tight roots restrict growth, reduce the amount of extension, and reduce the potential for an increase in mass, so even if we THINK plants are doing well because we use the stress of tight roots to get them to bloom or grow in a particular habit that we like, the truth is tight roots are stressful and plants would rather have plenty of room for their roots to grow so they could grow as mother nature intended. No one is more aware of the negative influence tight roots has on growth than the bonsai practitioner who uses that tool extensively to bind down the plant's growth habits so the will of the grower, not the plant, prevails. Using tight roots as a tool to achieve an end is all about the grower's wants, and not the plant's.

Interestingly, many mistake the fact that a plant seems to be extending it's parts and growing leaves for actual growth, but if the plant is robbing nutrients from other parts and shedding them in order to support new leaves or branch extension, it may not be increasing in mass, and therefore not growing ..... only robbing Peter to pay Paul.

If we chase 'root-bound issue' a little further, we can see the reasons that it is suggested that particular plants might like root-bound conditions. Tight roots alters the plant's growth habits, and the stress of tight roots can cause other physiological responses like bloom induction. Again, this is happening because of stress, and is the plants unhappy response. Bright flowers make the grower happy, but the plant's perspective may be entirely different.

Where I was really heading when I started to write this is: There is a relationship between plant mass (size), the physical characteristics of the soil, and the size of the container. In many cases, when we are advised that plant X prefers to be grown tight, we are being told that this plant won't tolerate wet feet for extended periods. Someone somewhere assumed that we would be growing this plant in an out-of-the-bag, water retentive soil, and "a big pot o' that soil stays wet for a long time, so we better tell these people to grow this plant in a tiny pot so the plant can use the water in the soil quicker; then, air will return to the soil faster and roots won't rot.

If you place a plant in a gallon of water-retentive soil, it might use the water fairly quickly, at least quickly enough to prevent root rot; but if you put the same plant in 5 gallons of water-retentive soil, the plant will take 5 times as long to use the water and for air to return to the soil, making it much more probable that root rot issues will arise. So lets tell 'em to grow these plants tight to save them (the growers) from themselves ......... because we KNOW they're all going to be using a soggy soil.

Key here, is the soil. If you choose a very porous soil that drains well and supports no (or very little) perched water (that water in the saturated layer of soil at the bottom of the pot), you can grow a very small plant in a very large pot and make the plant MUCH happier than if you were growing it tight. You still have the option of choosing those plants you prefer to stress intentionally (with tight roots) to get them to grow as YOU please, but for the others, which comprise the highest %, it makes much better sense to change to a soil that allows you to give the plant what it wants than to stress the plant so it won't die. That's a little like keeping your dog in a sleeping bag 24-7 to ensure he doesn't get cold.


    Bookmark   September 22, 2010 at 2:32PM
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Liebig's Law was written in 1828. It was written about chemical fertilizers. Its importance has long been abandoned due to the harm done to the environment by heavy use of chemicals.

"Liebig's Law was used to support the development of the fertilizer industry, to replace soil nutrient deficiencies with inorganic chemicals. But nowadays we know that applying ever-increasing chemicals to our soil is not achieving satisfactory returns. It doesn't take a lot of thought to realize that this is because the nutrients concerned are 'no longer the limiting resource factor.' We know that the excessive application of inorganic chemicals has had deleterious impacts on soil biota and that the availability of the appropriate soil foodweb is often the prime constraint on crop growth." - Dr Elaine Ingham, a leading international soil microbiologist. Soilweb International. 2009

University of California, Davis states, "LIGHT is probably the most important factor for indoor plant growth. In most houses, it's probably the most LIMITING FACTOR as well."

University of Missouri Extension, David Trinklein, Dept. of Horticulture states: "Lack of Adequate LIGHT is the most common factor LIMITING the growth of plants in many homes."

Texas A&M, Master Gardener Handbook by Douglas Fl. Welsh, Extension Horticulturist and Samuel D. Cotner, Extension Horticulturist state: "...most homes and offices are environments poorly suited to the needs of tropical plants...LIGHT is probably the most essential factor for house plant growth. The growth of plants and the length of time they remain active depend on the amount of LIGHT they receive..."

A simple Google, brings up hundreds of articles if anyone wants to look. Fortunately, these articles are more recent than 1828.

With dwindling daylight (goodbye summer) we need to address the difficulties of providing proper light intensity indoors to carry our plants over winter. Providing enough light to continue plant growth is not an 'easy fix.' Most windows do not provide enough light for healthy growth.


    Bookmark   September 23, 2010 at 1:39AM
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I'm not trying to be argumentative, so please take this in the spirit in which it's given.

Light definitely is a factor. Yet almost everything I've read about houseplants says that the majority of people kill their plants by overwatering. Not by under or over lighting.

My guess is that once people figure out how NOT to kill plants by overwatering, light becomes the next thing to figure out. But, that doesn't mean they've mastered great growing. They are keeping them alive - not helping them thrive.

Once you have minimal light and soil/watering down, now you get into optimizing. You can optimize every one of these factors - soil, water, pH, all nutrients, light - and to me the concept of Liebig's Law helps me see that all of them need to be optimized. If any aren't optimal, the plant's growth will be diminished. And the one that is the least optimized will prevent the plant from being all that it can be until it's fixed.

I don't see this as a discussion about whether Leibig's Law is valid in regards to modern fertilizer, but rather about how this principle illustrates how we can limit a plant's growth by not attending to all of the things that factor into its growth.

(It's late and I can't sleep, so please forgive any incoherent sentence structure, typos, or poor grammar, lol.)

    Bookmark   September 23, 2010 at 3:44AM
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The OP isn't making claims about which is the most important factor, simply that the most inadequate factor will essentially set a cap on plant health.

Sure, light is more critical to plant survival than, say, a magnesium deficiency. But if light, water and all other factors are perfect, they still won't cancel out the Mg deficiency; it will become the most limiting factor.

    Bookmark   September 23, 2010 at 4:22AM
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tapla (mid-MI z5b-6a)

I've said many times that light is a critical issue re plant growth, and no one has ever disputed that fact, that I can recall, so I don't know why it has to be a continual issue and argued again on yet another thread.

This is the container gardening forum, and in my experience, most of the discussions are about plants grown outdoors. No one ever disputed that light is an issue indoors, but even as light relates to houseplants, there is no need for a lengthy discussion to solve any light-related issues (as there would be with issues like nutrition or soils). If the plant isn't getting enough light, the solution is simple - move it. If it is getting too much light, the solution is equally simple - move it. If you can't move it, supplement the light it's getting. If you can't supplement it - live with it. What else needs to be discussed? (rhetorical) We've already allowed that light is very important and potentially, even commonly, a limiting issue. Why keep arguing it up again and again?

"Liebig's Law has been abandoned due to the harm done to the environment by heavy use of chemicals."

As kindly as I can say it, this simply doesn't hold water. Any perceived damage to the environment by heavy chemicals or fertilizers has absolutely nothing to do with Liebig's Law or the reaction of plants to limiting factors, and is no more reason to abandon Liebig's Law than it is to abandon the law of gravity.


    Bookmark   September 23, 2010 at 9:13AM
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calistoga_al ca 15 usda 9

It is unfortunate that Dr. Liebig has acquired the title of "Father of Fertilizer". I am sure he would be appalled. It is not true that he founded Monsanto Chemical Company. Having grown up here on this farm some 80 years ago our farm used chemicals scraped off the chicken house roosts(too often, by me)which we called fertilizer. Using "Liebig's law" we spread this very "natural" product on that part of the farm having the most gravelly soil, being the most deficient in nitrogen and unable to grow a stand of Oat hay without the yearly addition of Chicken manure. Al

    Bookmark   September 23, 2010 at 10:11AM
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There is a forum to discuss light issues for those really interested..I will link it for those not aware of it.
That is where I go when this light becomes an issue.


Here is a link that might be useful: Grrowing under lights

    Bookmark   September 23, 2010 at 10:47AM
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This forum is called 'Container Gardening'. My understanding is it should address all factors involved in growing well in a container, whether indoors or out.

We all agree plants cannot thrive when any one factor is limited. Therefore, lets cover all the 'factors.' There have been numerous, lengthy expositions about potting mix. There are other issues to growing well which should be explored.

Lathyrus, over-watering occurs when a someone waters faster than a plant can take up water. When a person waters without regard to growth, the plant will decline. Growth of the plant should be the determining factor behind watering. If all conditions are optimal for growth...good light, good air circulation, temperature it is difficult to overwater. The term 'over-watering' should be 'unnecessary watering.'

Winter, in a home environment, light intensity is almost always poor. My home has large, South facing windows which are shaded by overhangs. Others have windows shaded by trees or curtains. Most of us have low-lit homes. Our beautiful plants, which have grown so well outdoors all summer are now moved back inside. Light is poor and unless supplemented, we need to cut back on water and feeding. Plant growth has slowed or stopped and the plants needs have changed. The other 'factors' need adjustment.

In my zone 5-6, nights are getting cold, plants have slowed growth, the growing season is near its end. That is the reality of growing in this zone. A few warm days isn't enough to jump-start growth. The nights are the determining factor.

Growing plants is like growing children. The only expert is you. Take the good information and work it into your growing conditions.

The importance of good light and plant health is not disputed. It is always at the top list of successful plant growing. Most people do not research their plant before buying. They bring home a beautiful, green plant which slowly declines in their growing environment.

One needs to know where the plant is located. Has the grower tried to move the plant to higher light? Many times that is a simple fix and doesn't require supplemental light. Learn to water according to growth. That is a simpler fix than repotting in mid winter and is not necessary.

One cannot assume a grower has researched the plant they are trying to grow. You cannot assume the grower knows what the term 'medium/low light' means.
There are specific forums (thanks Mike) but specific forums, such as 'Growing Under Lights' is about using supplemental light. That might not be necessary for some people because they might have a better window to move their plant to.

I have had the most success as a grower by increasing light levels with all plants. Light is so overlooked. It always amazes me how quickly increased light will affect their health and growth. It isn't always 'simple' because most homes are underlit. Yet, I've seen plants turn around and start growing again with just a small increase of light. The increase in growth will quickly overcome the other limiting factors.


    Bookmark   September 23, 2010 at 2:26PM
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tapla (mid-MI z5b-6a)

Hi guys - I think NO ONE disputes the fact that light is EXTREMELY important. No one ever has, and no one is making assumptions, and I wouldn't be so presumptuous as to decide for (the collective) you what this forum should or shouldn't discuss, or whether one potentially limiting factor is more important to discuss than other potentially limiting factors. I think that is strictly up to the individual & that anyone would resent being told what they should or shouldn't discuss or how they should discuss it - but that's just me.

I'm wondering if I'm missing a point other than light is extremely important to plants and that I and/or the forum is remiss for not giving it discussion time equal to other potential limiting factors? If not, there is nothing I can see to fuss about. It's true that potting mixes have been well-covered, so why doesn't someone take the bull by the horns and put some effort into writing something lengthy and informative about light if they want it covered in depth/detail? Anyone? I already mentioned I'm not willing to do it because I don't think it would garner much interest, but what do I know? ;o) I'm guess I'm waiting for someone to bring light to light in such a way that we can take something positive from the information shared.

"I have had the most success as a grower by increasing light levels with all plants. ....... The increase in growth will quickly overcome the other limiting factors."

I have to offer comment on these thoughts, just as I found it necessary to comment on the assertion that Liebig's Law has been repealed or is no longer applicable. In the first place, increasing light will NOT improve growth unless light is THE limiting factor. It does no good to argue this point relentlessly unless you can show Liebig's Law wrong. Simply saying that increasing light will increase growth won't make it so, and is a logical error. If the plant is getting perfect light or too much light, increasing the amount of light will be counter-productive - just as a little more fertilizer is counter-productive when compared to the perfect amount; that too, is part of Liebig's Law. BTW - Liebig's Law is quoted, discussed, and referred to in many, many current university level texts, so it's still quite fashionable to put stock in it.

Over and over we see the argument put forth that 'the increase in growth will quickly overcome the other limiting factors'. This is not an opinion. It is another factual error. As I pointed out before, if this statement was true, we could grow anything we wanted w/o fertilizer or water at any temperature or pH in any type of medium from pudding to peppercorns - as long as the light was bright. There are a large number of cases where photo-saturation or photo-oxidation (too much light) are inhibiting growth, and a reduction in light improves growth. Here we see that too much light can also be a limiting factor.

I tried to keep this as on topic as I could and still refute some of the errors. There really is no need for the same point to be argued over and over by rearranging the phraseology - there is no point in it and it helps no one. I'd rather be spending time offering helpful information than arguing against the same erroneous information repeatedly.


    Bookmark   September 23, 2010 at 3:35PM
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I suppose it's my background as someone in a science field, but do you really believe that growing things is not a science? In your response you wrote, "Growing plants is like growing children. The only expert is you. Take the good information and work it into your growing conditions."

The only expert is certainly not me! I am but a learner on a journey of scientific inquiry.

I believe a few other posters have made this point, but I will make it again. This isn't about fertilizer only or soil only or water only or even light only. They all are limiting factors. Using the law as an analogy allows us to see that everything we do has an impact and it's up to us to find the most limiting factor and remove it, then look for the next, and the next, until our plants can grow to their potential.

Jane, I think I understand your frustration, but it seems you're throwing the baby out with the bathwater. I'm guessing that you are intuitive and tend not to follow an algorithm for how to do things. If it works for you, that's great. May people are very happy doing it that way. It doesn't work for me, though. I want the algorithm. I want the principles. It seems as if you're fighting against this approach.

I agree completely that growing is like raising children in that we all make our own choices. And, like raising children, many of us feel our method is a better method, which starts many an argument. And, just like raising children, I do believe that there is certain science that helps us raise healthier plants if we are open to it.

Of course, just my opinion.

    Bookmark   September 23, 2010 at 4:55PM
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Thank you Lathyrus for your kind and positive response. It is very refreshing.

I completely agree with this statement:

"This isn't about fertilizer only or soil only or water only or even light only. They all are limiting factors. Using the law as an analogy allows us to see that everything we do has an impact and it's up to us to find the most limiting factor and remove it, then look for the next, and the next, until our plants can grow to their potential."

My frustration is that this forum seems to only be about potting mix. That in itself is a limiting factor. When someone follows the directions and repots into gritty mix, they are not guaranteed success. Unfortunately, what I have seen here is the person is made to feel they did something wrong if their plant still is not doing well. Other 'factors' are not addressed. Until I started joining in, I have seen little or no reference to light, temps or zone. Now I notice it addressed more frequently. That is positive, in my opinion.

My comments regarding 'experts' has much to do with my feeling that growing plants is very dependent on variable factors we can't always control (weather, temps, climate). Raising children, I had my kids during the period of Dr. Spock and various other 'experts. Their theories/rules didn't fit all children or all parents. My degree is in Psychology and I studied and practiced their theories for years until I learned that one needs to be flexible and not bound by laws which have little relevance to what is happening in your life at a given time.

The 'expert' is always you. You ARE the control. You can have all the information in the world but in the end, you are in charge.

I don't get the point of Liebergs Law. What is the relevance? Nothing new there, such is life. Of course there are limiting factors which one, hopefully adjusts to improve a situation. Somehow, this was suppose to prove that light isn't as important as potting mix? I still disagree and that is my opinion based on MY experience. Light will always improve the other factors making them less detrimental. Increase light and air circulation, you will be less reliant on what the plant is potted in. You can grow in a shoe if you want.

I don't have a problem with researching. I wouldn't be a successful gardener if didn't have an intellectual understanding of basic fundamentals. I am always learning and encourage others to do the same. It is an ongoing process.

The sad reality is that many people do not devote the time or energy necessary to grow well. They lead busy lives and want a pot full of flowers. No matter how much time you devote to explanation, it usually goes in one ear and out the other. If you work with the public, as I do, you deal with those realities. You find a way to make their growing experience successful enough that they might learn something in the process and continue learning. That is always my hope.

I feel my experience is worthwhile and is the way I approach working with people and their plants. I give talks, classes and work hands on with people. I have methods which work and a good understanding of what doesn't. I believe encouragement and simple explanations go further in educating people than overly technical ones.

Its unfortunate that people with different opinions have to prove themselves here. I have found this whole experience frustrating and hurtful.

Again, Lathyrus I thank you for your cordial response.


    Bookmark   September 24, 2010 at 1:14AM
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If I may, may I focus on growing in container mixes for a moment..?
Nothing against anyone..:-)
Al, I know you won't mind..

Of the 26 e-mails and several nursery owners, experts, cactus and succulents club members, Orchard growers I have spoken to, all have told me that no matter how many variables there are in caring for their plants, their number one concrern is the "mix" they use..

Therefore, Bonsai West makes their own mix and will use nothing else for their plants while making a pretty penny selling it, their gritty mix, knowing that even in their greenhouses loaded with light and all the right ingredients, temps, fertilizer and so on, and for those of us using our homes, the number one killer of their plants is poor soil..

Mahonies sells their own professional blend that touts being better than MG mix, and they would sell nothing else..
Logees makes their own mix, and refuses to use anything else for their plants because of it's very good drainage properties.
Al makes his own.
I make my own mix.
Many make their own mix or use bagged soil mixes, and that is a main reason for a very helpful discussion stared like this, yes?

These stores will make me pay an arm and a leg for their special mixes, yet some here have generously and might I say gratefully shared these what could of been secret treasures, the heart of my plants, the soil mix, right here in threads started like this..

I have dozens of friends in southern states that can get all the light they want from California to Florida that come to threads like this because the mixes they use are failing or use to fail them.

Does anyone know what "akadama" soil "kunamah soil is? Have you ever used it? It is 42 dollars a bag for 15 pounds. The product is from China..Is it just as good as pumice, or turface, or perlite? Is it even worth buying? Thank you


    Bookmark   September 25, 2010 at 5:41PM
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tapla (mid-MI z5b-6a)

Hi, Mike. The thread was started as a clear way to codify things that can limit growth and vitality, and to illustrate the fact that many influences share the stage as equally important. It's probably pretty difficult to be off topic, because virtually any cultural influence can/will limit growth, as long as it is THE limiting factor.

Akadama and kanuma are forms of pumice or volcanic rock. They are both used extensively in Japan, either as a stand-alone bonsai soil or as a component that is mixed with other ingredients to reach the desired level of water/air retention. I'm sure that enterprising residents of Japan have also put it to use as a way to improve soils other than bonsai soils, just as we employ Turface, crushed granite, calcined DE, and other ingredients for the express purpose of improving the properties of drainage and aeration.


    Bookmark   September 25, 2010 at 8:05PM
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Thank you Al, and thank YOU forums for taking care of my request in a timely manner..:-)

Thank you!


    Bookmark   September 25, 2010 at 8:14PM
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alexander3_gw(6 Pennsylvania)

>It's probably pretty difficult to be off topic, because virtually any cultural
>influence can/will limit growth, as long as it is THE limiting factor.

Just to clarify, are you saying that there is no situation where, if two factors are suboptimal, that increasing either one would increase plant growth?

For example, is there any situation where either increasing water OR increasing nutrient X would both increase growth?


    Bookmark   September 26, 2010 at 12:28AM
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tapla (mid-MI z5b-6a)

If you refer to the picture of the barrel above, you can see that in this illustration, N is the limiting factor. It could just as easily be another soil nutrient, temperature, light, or soil moisture/aeration, but let's stick with the picture. If we add enough N to make the stave representing N as tall as the taller staves representing other nutrients, you can see that phosphorous (shown in the pic as phosphorous pentoxide because the P % of fertilizers doesn't represent actual P levels) would become the next limiting factor. Because we didn't increase the phosphorous levels, phosphorous has become the limiting factor. Add some phosphorous and the limiting factor shifts to Ca, the next shortest stave, so growth can only occur as fast as the Ca supply allows - as fast as THE most limiting factor allows.

The barrel only illustrates nutrients, but there are staves for other cultural factors as well. Temperature, light levels, soil moisture/aeration levels, pH, non-nutrient solubles ...... are all potential limiting factors.

I think it's a trap (not that you set one) to try to answer your questions about two conditions being sub-optimal at the same time. Yes they can be, but only one is limiting growth. If you improve the most sub-optimal condition, the one that wasn't quite so suboptimal will then be the ONE limiting growth. Look at it like this: Think of an automobile's forward progress as growth. If you're out of gas and have a flat tire, both conditions are sub-optimal, but in fact it's only the deficiency of gasoline that is limiting forward progress, because a vehicle CAN move forward on a flat tire. Add gasoline, and the flat tire becomes the limiting factor. Fix the flat tire, and your forward progress might then be limited by a faulty transmission that won't shift out of first gear. All of these factors are sub-optimal, but at any given time, only one is the most limiting factor and limiting normal forward progress.

Just what is being limited, would be a good thing to mention. Limiting factors affect a plant's ability to grow to its genetic potential. You might notice my regular use of the term 'vitality' when I write. It is actually a plant's vitality that we can hold sway over, not its vigor. 'Vigor' is constant. Mother Nature provides every plant its own, predetermined level of vigor by building it into each plant. Vigor is the genetic potential every plant is encoded with, and its measure is the plant's ability to resist stress and strain. Vitality, in contrast, is variable - a dynamic condition that is the measure of a plant's ability to cope with the hand it's dealt, culturally speaking. A good way to look at the difference between vigor and vitality is to look to genetics for the level of vigor and to things cultural for the plant's vitality. It's up to us to provide the cultural conditions that will ensure our plants' vitality. Vigor and vitality are distinctly different, and a good case could be made that they are unrelated, but there is no need to delve deeper into that point. A plant can be very vigorous and still be dying because of poor vitality. Far more often than not the term 'vigor' or 'vigorous' is misapplied, where in their stead the terms 'vital' or 'vitality' would have been more appropriate. Reduced vitality is what we witness when our plants are growing under stress or strain and in decline - under the effects of limiting factors.

I would like to take a moment to express my appreciation to the late Dr. Alex Shigo for his works, which have helped distill my understanding of stress, as opposed to strain, and vitality as opposed to vigor.

I mentioned the importance of learning what your plants potentially limiting factors are, so you can optimize them. I think now is a good time to talk a little more about limiting factors.

The most difficult factors for us to deal with are the least apparent, and the easiest to deal with are the most apparent. It's no wonder that the limiting factors most often discussed are the most difficult to deal with - the ones that seem most mysterious because we can't SEE what's going on. You can almost lump the most difficult into one category, but not quite. The most difficult issues discussed on the forum have to do with nutrition, soil chemistry, and the physical properties of the soil. I think we can probably tack insects and diseases to that list as well, since they are also frequent topics of discussion.

The easiest potential limiting factors to identify and deal with are light and temperature. The argument has been made that our homes are dark, but that has no bearing on our ability to identify and point out the plant needs more light. If we can't deal with it because we have no way to improve natural light conditions, we must supplement the light or live with it. The same is true of temperature - end of story.

To finish with Alex's last question: ".... is there any situation where either increasing water OR increasing nutrient X would both increase growth?" I think you meant: "is there any situation where increasing water AND nutrient X would both increase growth?"

Yes there is. If low moisture levels or a deficiency of 'X' were the two MOST limiting factors, that is to say on a scale of 1-50 they were #1 and 2, then increasing the supply of 1 and 2 will improve growth. Let's say water is 1 and X is 2. Increasing the supply of water will improve growth up to the limiting effects of X. Increasing water and X will improve growth within the limiting factor of whatever #3 is on the list. Here's the rub - simply adding X will NOT improve growth, because the lack of water is STILL the limiting factor. So even if EVERYTHING else was perfect, water would still be limiting. We can rotate any potentially limiting factor into water's #1 position and come up with the same scenario.

Take care.


    Bookmark   September 26, 2010 at 9:38AM
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Thank you, Al, for yet again revealing the simplicity in container gardening "science". Growing well becomes so elementary when the basics are covered. :-)

As a busy gardener who doesn't have much time to devote to my indoor containers, I have found that your suggestions allow me to worry less about the lack of time I can spend... and I still have very satisfactory growth results.

A shout-out to JoJo, Mike, and all my other friends here... you know who you are! If I'm not up to my elbows in roses and double digging, I've been flat on my back with sciatic nerve issues! I hope you're all having a wonderful summer! :-)

ps - my orchids in Al's Mix are budding!

    Bookmark   September 26, 2010 at 9:54AM
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Jodik.....WHAT!!!!!!!!!!!? Where have you been? Sorry, off topic...I will e-mail you...:-)))))


    Bookmark   September 26, 2010 at 1:28PM
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I would like to take a moment to express my appreciation to a generous man, you Al, for your works, which have helped distill my understanding of stress, as opposed to strain, and vitality as opposed to vigor.

I also would like to say that you repeated what my mom told me on this one....Lol
"If we can't deal with it because we have no way to improve natural light conditions, we must supplement the light or live with it"..
Even further, she said to get rid of them if I can't accept the change in them...
I was complaining to her about how much I hate bringing them in doors out from all that natural bright light, and how much my plants hate it too..
Certain ones sulk for a few days until they realize they are stuck indoors until I say when they can go out again, starting with my citrus and succulents..
Just as soon as I bring my colorful jades in, they revert to green.
Then some of my tropicals turn color my turning a bit yellow, light green, or both on me, sometimes dropping the oldest leaves..This happens everytime I bring one home from a nursery.....
Guess I have to live with it since I don't plan on getting a greenhouse, or putting on my artificial lights too soon. They are all at the mercy of my only two south facing windows and skylight..

I would say many grow quite vigorously all winter, but then their "vitality" that is deminshed could certainly be improved...I guess I am too cheap to improve the only limiting factor for my plants, more light at the moment...

Jodik, are your Orcahrds in the gritty mix/ I remember you saying you were going to try it..Please let me know..

I am glad to see you visited..


    Bookmark   September 26, 2010 at 1:55PM
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tapla (mid-MI z5b-6a)

Thanks, Jodi. Jodi hasn't been around much lately. I hope she starts feeling better very soon! We became pals after she had one of those 'AHA!' moments, either after reading the thread about container soils, or after she tried a bag of soil I sent her. I don't remember which - maybe both. ;o)
In general, this thread's reception has been quite positive, which gives me the hope we are back on track now and we can keep it that way. I enjoy sharing information and 'talking plants' for their own sakes. The kind comments do increase the level of enjoyment by adding to the sense that my offerings might be helping to increase the level of understanding, as well as the satisfaction, or even success others enjoy from their growing endeavors. Thanks, again. Take care.

Sounds like your mom is a smart lady, Mike. ;o)


    Bookmark   September 26, 2010 at 2:18PM
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puglvr1(9b central FL)

Hi Jodi!! I'm so sorry to hear you're not feeling well...hope you feel better soon! We've missed you!

Al, I absolutely Love that cute little plant and the pot...SWEET! Thanks for the photo!

    Bookmark   September 26, 2010 at 2:45PM
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Hello Everyone! Miss you guys, too!

Thanks, Nancy, Al, Mike, and everyone... your good wishes help! :-)

Well, Al... the positive attention you get is extremely warranted! I can't begin to tell you how much my growing has improved since that Aha! moment. I just wish I'd had it about 30 years ago! ;-)

The world of container gardening is rife with fallacy at one end, and rife with greed at the other. It was incredibly refreshing to read a simplified version of "how to" and a truthful "what you should know", all wrapped up in a few hearty articles by tapla! Once the how and the why are known, it's all so much easier and it all makes so much more sense. It's really a shame that the entire gardening world isn't on the same page, but unfortunately, most of it isn't even in the same book... or the same library, for that matter!

Anyway, I recall receiving a package from Al, and upon opening it and examining the mix, it all became clearer still... and I knew my bulbs would be happy. Since that time, I've planted everything in a varied mix of similar ingredients, and I've been very successful. Happy, healthy roots make for happy, healthy plants! It's just so elementary!

Off topic, I've been very busy expanding the landscaping to include a few hundred more rose varieties, which includes stripping sod, digging, amending poor clay soils... and I'm sorry to say that I overdid it and am having a little altercation with my sciatic nerve. It's winning so far, but I can't let it keep me down. I have to get some things done before winter!

Great pictures, folks! Mike, I'd try replacing that soil with a more aerated version. It appears to my eyes as though the roots have been exposed to too much moisture for long periods of time... meaning that the soil is too moisture retentive. It looks a little waterlogged to me... although it's tough to tell everything from a photo.

And yes, Mike... I did plant my Dendrobium orchids in Al's Mix... or my version of Al's Mix. It contains roughly equal parts fir bark, perlite, and granite chips. The roots are very healthy looking... I can see a few through the sides of the opaque pot I chose. The mix offers very good anchorage, and it seems to be the right mixture for the amount of moisture these plants need.

I also have a big box of akadama, the little clay balls, which I haven't tried yet. I've got a few Phals to go in it, once I find the right containers. I'm going for a semi-hydroponic trial. I may even mix some with the other ingredients and see how it looks and feels. In that case, I'd nix the semi-hydroponic method and just use it as regular medium.

Once snow flies, I hope to have some time to spend talking about gardening, instead of just doing it! Until then, I'll try to peek in every once in a while!

Happy Gardening!

    Bookmark   September 26, 2010 at 3:46PM
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tapla (mid-MI z5b-6a)

It's an Impatiens, Nance.


Streptocarpella - one of my favorites, but couldn't find one this year. :-(

    Bookmark   September 26, 2010 at 3:47PM
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puglvr1(9b central FL)

Gorgeous Al...thanks for posting! Love those purple blooms! Thanks for the name on the first one as well.

    Bookmark   September 26, 2010 at 5:50PM
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I agree, Gorgeous! How in the world do you all type bold letters and so on? I see no options to do so..A postcard picture!

Hi Pug!


    Bookmark   September 26, 2010 at 8:00PM
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puglvr1(9b central FL)

Hey Mike, sent you an email...:o)

    Bookmark   September 26, 2010 at 8:21PM
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Thank you Pug,

you were so kind to do that!

You too have helped me along with Al..
Just as Jodik said, you all know whom I owe a debt of gratitude too..;-)
Jodik, I will write you soon..I am so sorry to hear you have been under the weather..:-(

    Bookmark   September 26, 2010 at 8:54PM
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tapla (mid-MI z5b-6a)

I see I was posting at the same time as Jodi's last & missed her post. Thank you again for the kind words, Jodi. You know I appreciate it. I thought I remembered asking you (Jodi) what town you live in. I KNOW I should remember, but .... I'll see if I can help you find Turface.



    Bookmark   September 26, 2010 at 9:01PM
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Jodik, I never saw your post! I am so sorry..

I have been thinking about you a lot. If I lived near you, I would release the pain for you since I am a message therapist and relieve many of this dreadful pain, for free..I will e-mail privately..

When I reflect back too, I also remember recieving a free bag of mix from Al, and for me it all became foggier when I felt the heck will my plants survive in this?
I also received a free conatiner of great fertilizer and all the fixins.. With me,my response was one of greatfullness, yet at the same time, I never would beleive that the gritty mix could do anything!
I laughed actually and I was very apprehensive to use it for anything but my sick and dying citrus tree, only 6 icnches tall...Well, let's just say that lasted a month when I saw my that test trial tree go from almost dead to amzingly vibrant, in the same window with same cultural habits! I still have it.. That was my AHA day! I recognized that day that this changed my plants lives and my view of container growing forever! From there on I was on a hunt for the ingredients and begging for more information from Al and others here, sometimes a pain.. When I read back on my old posts from when I from started, I am in disbelief that that was me... I wish that would of happened for me 20 years ago!
I know what you mean Jodik..;-)

Now all those nuseries and plants men that sell the most exotic, tropical, fruit bearing plants owe a debt of gratitude to Al, since they have made a bounty on my spending habits! Yet I am running out of room, because this time around, they are not collasping on me anymore to make room for new

I am not afraid to grow anything anymore. I find myself resurecting many plants from the grips of death, keeping new ones healthy, and taking ones in that many people can no longer deal with, now that I have learned what can limit plant growth in containers..

Jodik, that is great that you can grow those in the gitty mix..Wow...I might try that.

Thank for your compliments and thanks for your advice..Much appreciated and surely missed from you...

Please get well, and come more often and continue to help us learn how plant growth is limited in containers..
You are extrememly valued here!


    Bookmark   September 27, 2010 at 9:00AM
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Thanks, Mike... I appreciate the good thoughts. I'm getting better as the days go by. As of this morning, I can almost walk upright! ;-)

I'm close to Champaign, Al... someone posted a while ago that I could obtain Turface in either Decatur or Bloomington, I believe it was... I can't recall which... but we never get out that way. Champaign is our usual stomping grounds for supplies, although we do hit the Rantoul area about once a month for flea marketing.

Thanks, though... I appreciate it. Honestly, the granite chips are perfect in size, and they do the job very well. Between the ingredients I've been using, I've got it down to a fair science, I think. I go to PetsMart for the fir bark reptile bedding... it's fairly cheap, and already cleaned and sifted... Rural King for the granite chips, which I rinse before using... and any store for the perlite. I only make small batches as I need medium, so it works out great.

Adjusting the moisture retention is as simple as adding a little vermiculite. At least, it works for me. My largest pot is probably a 12" clay, and my plants are mostly Amaryllids... with a few orchids thrown in the collection. Amaryllids are exceedingly forgiving when it comes to lack of moisture... it's over watering that usually does them in. I usually recommend growing them more as a person would a succulent.

And given that my Dens are budding, I'd say light isn't the issue. In fact, I can't really say I have any major issues... except, maybe, that I don't have enough space for the collection of plants I'd like to have! But who does?!

Since we're concentrating on roses outdoors, there's little need for mass quantities of potting medium... we're not at the greenhouse stage yet in our business, and annuals aren't our focus. One day, however, I expect to be back in the Rockford area, which is where the family is. I should be able to locate the same ingredients there. Turface is the only item I haven't run down, but I can't say I miss it overly much.

As always, Al, your flowering containers are gorgeous!

I have nothing in a container blooming to share... but I do have some lovely rose pictures... look at the saturation of yellow in this one! I wish I could recall its name offhand!

    Bookmark   September 27, 2010 at 10:09AM
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greenman28 NorCal 7b/8a

Welcome back, Jodi!
It's great to see you alive and nearly upright! ;)
The rose looks good enough to eat...


    Bookmark   September 27, 2010 at 10:29AM
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Unbeleivably gorgeous!

You know, it makes you sad to see the flower pass on...Amazing work in my opinion!

Thank you for that..My mother loves roses and I am sure she will save this picture for her backround on her computer...


    Bookmark   September 27, 2010 at 10:39AM
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Thanks, Everyone!

Mike, if your Mom loves roses, then set her up to click through my PhotoBucket Albums... they'll knock her socks off!

The link below is for my 2010 album, which contains mostly rose and garden photographs. Not many of the roses are named in the album, but the camera did a great job capturing the beauty!

There are several pictures of rose bouquets I cut and brought in to enjoy... those might make nice wallpaper or backgrounds. Although, that yellow rose is the brightest yellow we've got so far. It's amazing in person! There are literally thousands of rose and garden pictures in my albums... the choice could be tough!

Enjoy! And say Hi! to Mom for me... I hope she's doing well. :-)

Here is a link that might be useful: The 2010 Album - Mostly Roses

    Bookmark   September 27, 2010 at 11:58AM
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tapla (mid-MI z5b-6a)

It looks like you have some rose hipps mixed into your rose album, Jodi. ;o) Great pics - pretty blooms!!


    Bookmark   September 27, 2010 at 2:19PM
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puglvr1(9b central FL)

I agree with Mike... Just gorgeous!!I love them all.

Mike, you got it!! Good job!!

Thanks for the wonderful and beautiful photos Al and Jodi!!

    Bookmark   September 27, 2010 at 3:51PM
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You're welcome! What is gardening for, if not for sharing? :-)

    Bookmark   September 27, 2010 at 8:26PM
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Al, I was wondering..

When someone comes to you for a nutritional deficiency advice about their plants, like say yellowing leaves, I noticed that you take the time to explain the possible root causes of this problem..

You do just don't state what mineral is lacking as many do..Why is that?

Take for instance: In a certain thread on the citrus forum, someone actually posted pictures asking what the problem was with the leaves of his plants..

It was noted that he has a Me deficiency, and he was recommended to spray it with fertilizer containing this mineral..But instead of taking all aspects that can affect this uptake, this was the advice givin as in the case many times over when I ask certain people..

Many so called nursery owners and proffesionals can always blame the ferilizer.
But this was a case of someone using FP faithfully..
That fertilizer I am sure does not lack nutrients, considering mine never seem to have problems using it.

I actually caught myself teaching a nursery worker about other factors that can hinder certain nutritional uptake, and not to solely suggest someone give more of any one particular nutrient until they could understand the culprit behind it first..


    Bookmark   September 29, 2010 at 2:12PM
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Sorry.....I meant to say Mn deficiency on a citrus thread.

    Bookmark   September 29, 2010 at 2:16PM
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tapla (mid-MI z5b-6a)

I saw the thread you referred to & didn't comment.

First, when you're talking about a micro-nutrient deficiency, you're talking about elements that are generally not mobile. Sulfur, chloride, copper, zinc, manganese, iron and molybdenum are marginally mobile in plants, but only under certain circumstances. Most of the mobility in the elements listed is usually associated with the breakdown of amino acids and proteins in older parts of the plant, only under nitrogen deficient conditions. IOW, they're only mobile when the plant is robbing nutrients from old tissues before they are shed, and translocating them to other tissues via the phloem stream. Since these elements are essentially immobile during periods of adequate N supply, a foliar application (spray) really doesn't do much good. It can alleviate the deficiency temporarily by supplying Mn to the leaves it contacts, but unless it rinses off the foliage and enters the plant through the root pathway, it won't be present in the nutrient stream to ensure the normal development of new growth. This is the reason that, no matter what advertising claims are made, Ca spray supplements are so ineffective at eliminating BER. Ca is considered immobile in the plant, so if Ca is not in the nutrient stream as new cells/tissues are forming, the tissue will form abnormally, with weak cell walls and other issues - BER.

In the same vein as what you were mentioning, I don't like to advise people to use this element or that element to 'cure' an 'apparent' deficiency. Many 'deficiencies' aren't deficiencies at all, only symptoms of cultural inadequacies; or, they are deceptive, varying widely in symptoms, and even then, many of the symptoms overlap. One of the first things experts will agree on is that diagnosing many nutritional deficiencies is little more than a crap shoot w/o the benefit of tissue analysis, so there is a good chance the diagnosis will be wrong. Second, adding individual elements can easily affect the uptake of another or create a toxicity. E.g., if someone had applies an Fe supplement to try to 'green up the leaves', he might have unwittingly have caused a Mn deficiency. Fe and Mn are known as classic antagonists, and a deficiency/excess of one can affect the uptake of the other. Adding Mn only can affect the uptake of Fe, P, N, and other elements as well.

It just makes much better sense to me to use a fertilizer that supplies the elements most apt to be deficient in container media, or to use a fertilizer like FP, that ensures all the essential elements plants take up via their roots are available in a favorable ratio. Ideally, when one element is getting to the point it is in short supply, they all will be - at the same time. Using fast soils that allow you to water so you're flushing excesses out before you fertilize again, helps to keep the ratios in balance, so there should never be a need to supplement individual elements. Plants DO take what they need and leave the rest, but it is decidedly in our favors to keep 'the rest' at a minimal level.

If the person is actually using FP on a regular basis, it's unlikely there is a Mn deficiency unrelated to pH. Like Fe deficiencies that occur when using soluble fertilizers (they all contain Fe), the Fe is in the soil, but unavailable. Mn is affected by pH in the same way as Fe. My advice would have been to flush the soil thoroughly and fertilize; or, if the grower really was using the fertilizer regularly and at adequate solution strength, to add enough vinegar to bring the irrigation water pH down to 5.8-6.0.


    Bookmark   September 29, 2010 at 5:36PM
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Would foliar application of micros be useful as a diagnostic tool? If a plant is deficient in a particular element, feeding it to a leaf should help that leaf, and you can start trying to figure out why the element isn't getting absorbed; if that wasn't the problem, it should have no effect.

Edit: I initially put my reply to the original posting here, as an edit. No point in running us out of the 150-per-iteration limit faster than necessary, right? Oops. While I was adding my reply to the OP, Al slipped in with a reply to my question. So now I'm moving my reply to the OP into a separate posting below.

This post was edited by dsws on Mon, Jan 7, 13 at 16:15

    Bookmark   January 7, 2013 at 12:49PM
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tapla (mid-MI z5b-6a)

Sometimes - and that's frequently discussed - especially as a way to check for Mg deficiencies, even though Mg is not one of the minors. How well it works depends on how able the plant is to absorb topically applied nutrients (varies widely by plant) and the nutrient's mobility in the plant. All deficiencies are not directly related to a scarcity of the element that shows up as deficient. Deficiencies can be related to cultural conditions (pH, soil compaction, root congestion, temperature, presence of an antagonistic element in excess .....)

If you find foliar applications of nutrients helpful, you really should take a close look at your o/a nutritional supplementation and the condition of the primary pathway (for nutrients) into the plant - roots.


    Bookmark   January 7, 2013 at 2:15PM
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Thank you. I'm on a learning binge as I get back to having a few houseplants, and trying to pull together what I remember about plant biology from college. So I'm not coming from any practical experience of needing (or seeming to need) foliar supplements.

Speaking of pulling together what I half-remember from college, I'll get back to the OP --

Liebig's Law is useful, and usually (maybe always) a very good approximation to the actual truth. But we do have a better understanding now than we did in the mid-1800s.

Plants actively transport ions into their roots. They spend energy to do so. They have to transport that energy from their above-ground green parts (basically leaves, but also stems) to their roots. The roots basically have an energy budget, with which they have to supply all the mineral needs for the above-ground parts. As an element becomes scarce in the soil solution, the plant has to get it to diffuse from farther away. The energy cost of doing so increases exponentially.

"Increases exponentially" is an idiom meaning "suddenly gets impossibly huge". There's a reason for that: it's a pretty good description of what exponential increase does. But it's a continuous function, not a discontinuous leap. So there is some increase in the energy cost of importing an ion, as it goes from abundant to less-abundant. So it isn't a barrel-staff getting cut off straight at a particular height. It's more like a barrel staff that leaks around its edges a little, even before it reaches the top.

Then there's the income side of the energy budget. To make chlorophyll, plants need nitrogen and magnesium. But, when nitrogen or magnesium is the main limiting factor, I'm pretty sure each chlorophyll molecule can do a little more if there are more accessory pigments per chlorophyll molecule -- at least if the light isn't bright enough to keep them working at their maximum rate with only the usual ratio of chlorophyll to accessory pigments. More importantly, photosynthesis is often limited by the amount of CO2 the stomata are letting in, which in turn is often limited by the amount of water the plant can transpire, which brings us back to the energy budget of the roots.

So once again, the various factors do interact, and Liebig's Law is only an approximation, not the final word. Certainly good enough for practical purposes, though.

    Bookmark   January 7, 2013 at 4:11PM
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