Growing in Containers: Organic vs. Synthetic

enoughcliches(Tropical)February 10, 2007

I plant most of my ornamentals in the ground and use organic gardening methods. However, I do have a few that grow in containers on the porch due to their low-light requirements (we have *lots* of sun here). I have seen some forumers mentioning that organic fertilizers are innapropriate for use in container plantings because the growing media simply does not support enough microbe populations.

If that is true, I wouldn't mind making an exception for my containers and use slow-release synthetics, but what I'm concerned about is the micronutrient needs of the plants since most synthetic fertilizers only supply NPK. Will using synthetics necessitate the incorporation of compost when potting and the periodic addition of a compost mulch?

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stressbaby(z6 MO)

A couple of years ago, in order to supply micronutrients, I tried compost in a group of containerized citrus. The end result was an anaerobic soup in the bottom of the container.

I don't know about microbe populations, but in order to supply enough trace elements you have to use a lot of compost and this "clogs up" the mix and reduces the aeration. I use Micromax, a long-acting, granular trace element mix. Or you could use Osmocote PLUS or similar slow release fert with minors.

    Bookmark   February 10, 2007 at 8:39AM
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It depends a lot on what you use for your potting medium. As an example, I use a bagged organic container soil (Gardner&Bloome) that has components that contain and support soil microbes - bark fines, forest humus, worm castings, peat, chicken manure, bat guano, kelp and alfalfa meals, etc. So I fertilize with an organic fertilizer. To be honest, there is sufficient nutrient content in this mix so that adding more at potting has not been necessary, but I supplement during the season with a liquid organic product available through the same distributor. Both the kelp meal and bat guano provide a wide assortment of trace elements.

I doubt this high quality organic soil or a similar formulation is widely available throughout the country - many commercial potting soils are sterilized mixes and/or primarily peat based, so are unlikely to support much in the way of soil microbes. In years past, that used to be all that was available here, also. With these types of soils I also used Osmocote Plus with good success.

I'm not sure I'd be overly concerned about deficiencies in trace elements for container plantings unless they are long term or permanent plantings. Repotting and refreshing the soil periodically in these cases should help.

    Bookmark   February 10, 2007 at 9:42AM
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So, it *is* possible to support enough soil microbes in containers to make organic fertilizers viable? If so, that would save me the trouble of choosing synthetics, which I'm not exactly familiar with anyway. I use a blend of wood-based compost, chicken manure, guano, coir fibre+peat, perlite and vermiculite as a potting medium.

As for your Gardner & Bloome soil, if it's not widely available throughout the US, I'm pretty sure I'm not going to find it here either! Might have better luck with Osmocote Plus, though.

Since my climate it tropical rainforest, most of my container plantings *are* long term or permanent. You mentioned "refreshing" the soil. How would I go about doing that without changing pots or pot sizes?

If I was in doubt about the microbe activity in my containers, could I use a combination of organics and slow-release synthetics without hurting the microbes?

    Bookmark   February 10, 2007 at 10:34AM
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Since my climate it tropical rainforest,

Stop the train!!! ;-)

If you live in a tropical rainforest maintaining a microherd isn't much of a concern. You live in a microherd area ;-)

Chicken manure and guano are both rapidly consumed. The only issue with organics in containers are with the woodier materials that take a while to break down. In containers these are not likely to supply sufficient nutrients fast enough and their humusy, soil conditioning properties aren't really needed in a container mix.

There are many water soluble organic nutrient sources from seaweed, fish emulsions, liquid poop solutions, you name it. All of these will work fine in containers.

I think you will do just fine with what you are planning to do. Once you have done it you will doubtless form ideas, based upon your observations, as to what you might like to try differently the following planting. Since my climate it tropical rainforest, most of my container plantings *are* long term or permanent. You mentioned "refreshing" the soil. How would I go about doing that without changing pots or pot sizes?

You will need to repot and change the soil once it has collapsed. Long term plantings (those that you don't want to repot until the roots of the plant require it) need a container mix that is largely inorganic and stable. The reason potting mixes need to be changed is that the constituents are not stable and they break down into smaller and smaller particle sizes and they end up holding water to the exclusion of oxygen, particularly at the bottom of the pot (because the smallest particles find their way down there).

    Bookmark   February 10, 2007 at 11:00AM
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Whoa! For a second that, I thought you were telling me to stop announcing that I lived in a tropical rainforest climate! Don't ask me how I made that weird connection (train = trop. rain). Must be overexposure to sun from gardening during the current drought :P

So what you're saying is that the more long-term a planting is, the more inorganic/stable the potting mix should be *if* I want to avoid having to change it too often. Would I be pushing it too far to use organic fertilizers in a primarily inorganic medium? Or is the microbial activity here really so high that even that might work?

    Bookmark   February 10, 2007 at 12:04PM
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tapla (mid-MI z5b-6a)

I was invited to discuss nutrient supplementation on another popular gardening forum very recently. The reply I left is rather appropriate to your wonderings, so I'll post what I left there: If what I leave you with finds you with additional questions - please ask.

I get asked this question frequently, or a variation like: "I want to feed my plants the best - what's best & how often should I feed?". Most people queried, would look right past the question and hand you a box or direct you to the fertilizer section of a plant store for "plant food".

Actually, you cannot feed your plants. Food provides energy - fertilizer does not. Plants manufacture their own food during the process of photosynthesis when the pigment chlorophyll traps the energy of the sun in a molecule of carbon dioxide and water. The result of this miraculous reaction, without which the earth would be uninhabitable, is a molecule of glucose - sugar - a carbohydrate - photosynthate. The molecule acts just like a battery, storing energy from the sun that can be translocated to all living plant parts for immediate use, or stored in living cells - roots, leaves, and cambium for later use.

In order for a plant to make and use food efficiently, certain elements need to be available to the plant. In fertile garden soil, it is likely, even probable that that the nutrients will be available in a usable concentration. In container culture, it is a virtual certainty that we will have to accept the responsibility for providing nutrients in usable concentrations for the term of the planting if we are to expect plants to grow at or near their potential genetic vigor.

The three main elements or compounds that are needed for plant metabolism are nitrates, phosphates, and potassium (NPK), and they represent the bulk of ingredients in balanced fertilizers. We term these ingredients macro-nutrients, sometimes referred to as "the majors". Also included in the macro-nutrient category, but necessary in lower concentrations are magnesium, calcium and sulfur. Rounding out the list of nutrients needed to keep plants healthy are the micro-nutrients, or "the minors". These nutrients include iron, boron, zinc, copper, manganese, molybdenum, chlorine, cobalt, and nickel. Please note that some of the minor elements, or micro-nutrients are required in such minute amounts that deficiencies are rare in garden soils, but more common in container media. For that reason, it is good practice to insure that you use a fertilizer that is complete, including the minors. If the minor nutrients are not listed on the fertilizer package, and youre unsure that your soil contains an adequate supply, an excellent way of providing the minors while furnishing major nutrients is to use a granular soluble or insoluble product (e.g, STEM or Micromax). Organic fish and/or seaweed emulsions as part of your supplementation program can also be effective, but here I'll concentrate on the major elements.

Now that we've have seen that fertilizer is not plant food, but a way of delivering some of the raw materials or building blocks that plants need to make their own food and keep their systems orderly, I'll briefly say that it is important that we insure the soils we use contain adequate/appropriate volumes of air and water so as to make nutrient uptake possible and efficient, but that is another subject I won't dwell on today.

You can probably use a schedule or timetable to fertilize plants & have them be reasonably happy, but I use a different approach. If you do choose to fertilize on a regular schedule, it makes no sense to continue to fertilize when plants are quiescent due to chill, heat, or other unfavorable cultural conditions, Under these conditions, you might extend the preset intervals. Plants need more nutrients when robust and actively growing and less when they are "coasting".

I use a two-pronged approach to my fertilizing. The first thing I do is note leaf color of older leaves. N is a very mobile nutrient in plants. When it is deficient, plants "rob" it from older leaves to use in the production of new vegetative growth. So, when I see a lightening of leaves toward a lighter green or yellow, especially older leaves, and I'm sure that other cultural conditions are what the plant requires for good vitality, it indicates to me a need for supplemental nutrients.

A simplification of how I fertilize is: I attempt to get a higher percentage of N to foliage plants or those that are being grown for a reason other than blooms or fruit. Highly nitrogenous fertilizers support the plant during the growth of leaves and foliage. For flowering/fruiting plants, the phosphatic portion of fertilizers aid flower/fruit production, so I'll usually include the intermittent use of a fertilizer with higher percentage of P. Potassic compounds (K) stimulate the growth of roots and are included in adequate percentage in all complete fertilizers I use.

I use both chemical and organic fertilizers. As noted, but worth repeating, I determine the need for fertilization by leaf color. When leaves lighten and fertilizer is needed, I mix a recommended full strength solution of 20-20-20 soluble granular fertilizer and add a full strength solution of 5-1-1 fish emulsion in the same mix. This mix, I'll apply to foliage plants & plantings that are not dependent on blooms for their beauty. This is pretty much my standard for these plantings. For blooming plants, I'll use the same 20-20-20 fertilizer with a 2-3-1 fish emulsion included - UNLESS leaf color is good. If leaf color is good - I'll substitute a bloom-inducing, soluble formulation like 10-52-10 or 15-30-15 and still use the 2-3-1 emulsion. In all cases, I'll apply these solutions to well-hydrated plants growing in moist or damp soil, thoroughly saturating the entire volume of soil in the container.

I prefer the reliability and immediate action of the chemical soluble fertilizers for results, but understand the wont of some to remain organic. Generally speaking, organic fertilizers do release nutrients over a fairly long period, but there is a potential and considerable drawback in depending solely on them. They may very well not release enough nutrients to give the plant what it needs, when it needs it for best vitality. Organic fertilizers depend on soil organisms to break them down into elements the plant can assimilate, so most of them are effective only when soil is moist and soil temperature is warm enough for the soil organisms to be active. This soil organism population is a boom/bust proposition in container soils due to the extreme variables of temperature, moisture and pH. Nutrients in chemical form are immediately available for plant use and exhibit no dependency on soil biotic activity for availability. Plants do not care whether their elemental building blocks are provided in chemical or organic form.color>

Additionally, practices that promote high population numbers of soil organisms that feed on organic particulates hastens soil structural collapse, which is certainly counter-productive to your need for an extended-life soil. When I think of soils that must last long term, I immediately consider the percentages of organic:inorganic componants. If I want a soil to last several years, I'll use something with more than 2/3 inorganic parts, like Turface, pumice, perlite, Soil Perfector, etc., and only 1/10 - 1/3 organic parts - usually fir or pine bark. For plantings of 1-2 years, I'll use a mix of primarily bark, peat, perlite.

Well, I certainly never intended to go on so long; and I know I bored some into leaving before they got this far, but for those that made it to the end, I hope my thoughts were clear enough to provide some insight.

Al Fassezke

    Bookmark   February 10, 2007 at 1:43PM
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I found a new product called ZeoPro. It is a combination plant food-soil amendment-fertilizer-soil conditioner-slow release fertilizer which has been invented by NASA. AN ALL NATURAL PRODUCT. Sounded too good to be true but I've been using it for a year and works great for container growing. I noticed an increase in the flower and vegetable production. It's all natural, keeps the soil aerated and holds moisture. It does not break down. In my opinion ZeoPro solved a lot of my container growing problems. Definitely healthier, larger plants.I have purchased several bags from Tindara Orchids.

    Bookmark   February 10, 2007 at 8:42PM
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Would I be pushing it too far to use organic fertilizers in a primarily inorganic medium? Or is the microbial activity here really so high that even that might work?

No, you are not pushing it too far to use organic fertilizers in a primarily inorganic mix, IF you use only those fertilizers that rapidly become available to plants like fish/seaweed emulsions. You could pour it on the sidewalk and it would get consumed in no time. I don't think it is really of any concern what the potting medium is as far as microbe populations. If you think about it the soil is mostly inorganic and the microbes are there. Add a little compost/manure and their population and activity level skyrockets.

As for the microbial population in your area, I really don't know for certain that the population is higher than elsewhere, but constant warm and humid/moist along with lush vegetation tends to favor high activity from microbial life.

In the cold north where I live this is evidenced by compost piles that mostly sit unchanged during the winter and in summer they shrink before my eyes.

I am guessing that in your climate you could make compost very rapidly.

    Bookmark   February 10, 2007 at 10:09PM
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organic_tosca(9/Sunset 14)

Regarding GardenGal's reference to Gardner&Bloome potting soil: I've been buying it (in Central California) at a nursery called "The Greenery" in Turlock. I had never run across it before, and I'm sure it would not be in Lowe's, Home Depot, or Osh, but I like it very much. Having said that, I have to admit that I'm pretty much a newbie to outdoor gardening - a few pots on a balcony was about the limit of my experience until the last couple of years. Since then, I've had some disasters and a few successes, but this year I have higher hopes. Certainly my tubful of California Poppies (which I planted last Fall) are flourishing!

    Bookmark   February 13, 2007 at 7:30PM
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Since then, I've had some disasters and a few successes, but this year I have higher hopes.

Y'know, us gardeners have an awful lot that separates us in terms of our opinions, preferences, practices and priorities, but if there is any one common denominator that all gardeners share, it is what you just expressed.

We have our failures, our successes, but there is always next year or the next plant.

    Bookmark   February 13, 2007 at 10:50PM
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chilliwin(EU DK 7)

I like this thread.


    Bookmark   January 23, 2013 at 9:03PM
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tapla (mid-MI z5b-6a)

Why not bump it? ;-)


    Bookmark   January 23, 2013 at 9:50PM
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chilliwin(EU DK 7)

Al, your post is delightful. Many new container gardeners may have this question of organic vs synthetic. I hope they can find the answer from your post.

I am not a good cook but I like good food :)



    Bookmark   January 24, 2013 at 4:16AM
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