Potting Soil & Nutrients

saoodhashimSeptember 27, 2013

Before I start off with my question, I wish to give some introductory information

I am a new gardener (starting with container gardener on the roof as I don't have any garden space) living in the hot climate of Saudi Arabia in Al Khobar (these days the highest temperature over here exceeds a bit above 100F - Ranges from 75-103 and expected to remain that way until mid of October). The lowest temperature will be 50F in January.

Not much options for me with the potting soil over here. When I read discussion or articles about container gardening I hear a lot about Miracle grow and Liquid fertilizers and potting soil being fertilized or not. Bone meal, blood meal etc. etc. Frankly I am not able to understand how this works.

The people at the local nursery are also not educated enough. They just follow what they have been following for ages without much thought on NPK, Secondary and micro nutrients etc. So there isn't much local help either.

After that introduction, my question is, I have access to two brands of potting soil. One of the potting soil says that it is enriched however it can be fertilzed with a liquid fertilizer once or twice a week. It also says it is suitable for planting vegetables. The other information available on it is 95% organic matter, Ph 5-6, Ash content - less than 5%.

The other potting soil (according to German standard - as claimed) is a bit more sophisticated whose constituents are described on it as follows:

91% Organic dry matter, moisture content 70%
PH 6-7
N,P,K - each more than 0.21%
and then a list of secondary and micro nutrients described as PPM.

I am growing vegetables - starting with tomatoes, pepper and cucumber and as the weather gets a bit cooler, with peas, carrots, potatoes - all in containers.

My question is how to transplant the small plants that I buy from the nursery into the pot? Should I just transplant it in the potting soil without any fertlizer or should I add fertlizer also at the time of preparing the container for the first time? How often do I need to fertlize? When does fertlization start? Or is fertlization not required or required very late when the fruits set it?

The local nursery guys tell me to transplant the plants in the first one and put fertlizer after 1 month - once a month - by just sprinkling on the sides of the plant.

Btw the way fertilizer options are also quite limited here and we have either 100% composted cow manure or NPK pellets, The nursery guy is recommending using cow manure.

Also can you help me better understand how much NPK and other secondary and micro nutrients are required in a container of lets say 1 gallon? As a percentage of the total soil? or some other way to understand. This German standard potting soil says 0.21% each of NPK. Does that mean that NPK required only about 0.63% - which would make around - well it would make are 0.25 litres approx for each gallon of soil. Is this what is required in reality? It feels so less.

It would be a great help from the GW community to help me out in this area. I will certainly appreciate it.



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Oxboy555(Las Vegas)

You face a lot of unique challenges, but with some luck and ingenuity, you can probably make it work decently. Your veggies may not thrive, but you should be able to get something to harvest.

Sounds like it will be tough to build or buy a soil mix composed primarily of small bark pieces, which is advocated heavily on this forum. You might want to read up in this forum about the Gritty Mix, and try and build something comparable to that, finding substitutes where possible. Fortunately, your hot dry climate should aid in keeping the plants from sitting for long in soggy soil. Extra water retention is a pariah to most growers but in places like yours and mine (Las Vegas), it can help to a degree.

Once you have the soil figured out best you can, deal with the fertilizer. I think that cow manure in a pot would be rough. I'd say stick with the pellets and go light, if at all. All that organic matter and added fert already in the soil might take care of your single-cycle nutrient needs for you.

You should also try and figure out the pH and alkalinity of your water. If both those are considered high, you can a little vinegar to your watering source to help your plants take up nutrients better.

    Bookmark   September 27, 2013 at 4:31PM
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Thanks Oxboy for the respone.

I will try looking for the Gritty mix as guided by you.

However, since you mentioned about water retention, I have one another question.

The container gardening books and the general internet research tells me to water the containers / pots untill we see water flowing from the drainage holes. I do the same way. However, I realized that by doing this the excess water that gets into the pot waits there untill it drains out. This might be taking an hour or two - may be three it the pot is big. Is it ok for the plants to sit for that time under heavy watered soil.

Thanks again.

    Bookmark   September 28, 2013 at 3:23AM
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Oxboy555(Las Vegas)

Are you saying it takes a couple of hours for your pot to finish draining?

I have some pots where I think it's finished draining in 30 seconds, dump out the saucers, then come back in 3 hours and find the saucer full again. I think it's a function of a lot of things like soil composition, depth of the pot, size/number of drainage holes, "thirst" of the plant at the time etc. I don't worry too much about it as I'd rather water more often with excellent drainage than the reverse of fewer watering sessions and more water stored up in the soil.

The most important thing is to find that perfect balance between water retention in the soil and evacuation of water out the drainage holes for your specific situation/climate and the health of the particular plant. This is why the constructed soils like the Gritty and 5-1-1 make such a great base and starting point (and often ending point) for those of us who live in unique climates like the hot, dry desert.

    Bookmark   September 28, 2013 at 7:00PM
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For the purpose of clarity, are you trying to say that finding the bottom saucer full of water after 3 hours is not a matter of concern? And that if the soil is soggy for 3 hours it not something to worry about as long as it drains out of the holes? I felt that way when I read the first part of your paragraph and then later got confused when you said that you would rather water more with excellent drainage rather than less with more soggy soil.

I am a bit confused. Sorry for that :)

    Bookmark   September 29, 2013 at 8:03AM
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Oxboy555(Las Vegas)

Water in saucer after watering -- not a concern. In fact, up to 20% of the water per irrigation session should end up in the saucer (or better put, outside the container through the holes) each time you water.

Leaving water in saucer after watering - big concern IF said water is in contact with the container medium through the drainage holes. This usually happens when the pot bottom sits flush against the top flat surface of the saucer. Best options are to elevate the pot up off the saucer with rocks, pebbles, blocks, etc. Or locate the pots on turf or gravel in which the draining water can just sink into the ground.

Soggy soil is always a concern. Damp soil in a hot, dry environment -- not as a big a concern if the soil is able to dry out in 2 or 3 days, at which point you should be watering again. If you manage to construct a porous soil like the 5-1-1 or Gritty, you'll probably be watering daily in summer.

    Bookmark   September 30, 2013 at 1:39AM
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It certainly clarified. But if you dont mind I have one more question.
Lets say the pot was sitting on the saucer and the saucer had 1"-2" of water in it. How big is it a concern if it sits like this for 2-3 hours once in a while - like once / twice a week or so. Is it really something to be overly worried about? If this happens once a week, can I feel okay with it that it wont affect my plants growth?

    Bookmark   September 30, 2013 at 2:43AM
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drew51 SE MI Z5b/6a

If the saucer dries in 2-3 hours it is not of concern. it is so hot where you are at, it is probably beneficial.
I think the wisdom of Al and Josh, what they say is know your soil. That is the best wisdom. I would think 5-1-1 or gritty mix would not work in your conditions. You want the muddy mess they are trying to avoid. Which is extremely ironic to me. I have been trying to make this point for over year now. My point is it's not the soil, fertilizer or PH. You do need to know and understand those aspects, but it is the grower that really makes all the difference.
Most of my decades of experience is in growing cacti. I would love your conditions! Mine are just the opposite!
I learned about PH, fertilization, and soil from the great growers in that area. Even though not really related, but full of practical knowledge is this report on Fertilizers and acidification. The information may not help you at all, but is a good read for anybody growing acid loving plants in pots.
Cacti, blueberries etc. I would not follow advice for anything else. I tried it, and Ammonium sulfate is just too strong to use for other plants IMHO. But the info on water is useful to us in the USA as most of our water is basic, and a problem for acid loving plants. Most plants don't care. I happen to grow cacti and blueberries so found the info essential!

Here is a link that might be useful: Fertilizers and acidification

    Bookmark   September 30, 2013 at 6:55AM
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So that means a 2-3 hours soggy soil which ultimately dries out because of the heat, is not a point of concern. Infact it is beneficial? Now this is against conventional wisdom that I have been able to gather from the internet research that I have been doing for the past 2 months or so?

As a matter of fact, since most of the good gardening books and good garden website and articles have been written by US authors, they generally don't provide any material details about growing in hot weather climate. I did find that many of the things written in the many books and articles that I have read were actually not at all applicable to my conditions and by the same token many things which needed to be addressed have not been even touched upon :( And perhaps this anti-conventional wisdom stuff that you narrated is actually one of those matter not touched upon in the "For Dummies" books that I read from cover to cover :) Actually I picked up those "For Dummies" books because I thought they would cover the subject from a dummy's perspective. It so turned out that they did cover...... but only from the dummy's perspective who lives in USDA zone 4-8 :)

    Bookmark   September 30, 2013 at 7:13AM
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Frankly after your post, I am rethinking whether the second knuckle soil moisture test is applicable for me. I should actually be testing the soil surface for moisture and water it if dry. The local garden shop people do it that way. I never find them digging deep to figure out the moisture level underneath.

I also read that if you are in doubt that whether it is moist or not, tilt towards the moist side and donot water. I think in my case, I should be tilted towards the dry side and water it.

    Bookmark   September 30, 2013 at 7:19AM
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Oxboy555(Las Vegas)


I can only relate my experience doing container gardening living in hot, dry Las Vegas, but I think some of the same principles will apply to you.

Water sitting in a saucer is bad if the bottom of the pot is not elevated up off the sitting water's surface. It doesn't matter if it's 3 minutes or 3 hours. In my experience, even 1" of water in a saucer will not evaporate in direct 115degree Vegas heat inside of a couple of days. You would think it would, but for me it doesn't. Two days is way too long for my pot bottoms to be marinating in their saucers.

I am anal about emptying saucers or making sure the pot bottom is up off the standing water either with blocks or pebbles. I want that salty high-alkalinity water away (and all the salts/impurities/wastes picked up from the soil, etc) from my pot soil as soon as possible with zero chance of it sucking back up into the soil through the drainage holes.

The Gritty outside in the extreme desert is not really an option except for maybe some really hardy cacti/drought tolerant plants. It works ok for houseplants inside in the desert. The vanilla 5-1-1 works ok outside but you're going to need to water everyday in summer most likely, especially if the pot gets more than a few hours of direct sunlight. The 5-1-1 works great indoors in the hot, dry desert.

Drew's advice about the "muddy mess" in the desert is bad except for plants that tolerate soggy conditions.

    Bookmark   September 30, 2013 at 1:41PM
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Oxboy555(Las Vegas)

To your other question, unless the plant is obviously wilting or thirsty, wait an extra day to water. Soil that feels dry to us still has some moisture in it that the plant can use. Your plant will appreciate the extra day of air down among its roots.

    Bookmark   September 30, 2013 at 2:33PM
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Thanks Oxboy for your continued help. I really appreciate it.

Just one more question, because of the heat over here, while the inside of the soil may not be drying up, the top part of it become very dry, such that it starts to fly around in winds of 20 kph. In order to keep it moist and a bit heavy, should I sprinkle some water to keep the top part moist? or is there any other better way to address this?

    Bookmark   September 30, 2013 at 2:47PM
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Oxboy555(Las Vegas)

Do you have access to some kind of mulch? I use a 1" layer of shredded bark mulch to keep the soil tops cool of my containers that get some summer sun. The key is to keep any organic mulch out of the soil so it doesn't steal nutrients. Laying it on top keeps the roots cooler, helps prevent evaporation and in your case, should keep the soil from blowing out. I suppose your bark chunks should be pretty good sized - maybe 1" to 3" - to keep from blowing out.

You may be able to use rock or gravel as mulch too, but I don't have any experience with that.

    Bookmark   September 30, 2013 at 4:58PM
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I was thinking of keeping Newspaper. Would that be ok? I may need to remove it wile watering but I can manage that.

Btw, I read on many internet posts and books to water in the morning and evening (preferably in the morning) and not water during the day. Now I usually water only in the morning. But a couple of times it has so happened that I have felt that the soil is moist 2 inches below the surface of the soil in the morning but by around 11 am to midday, the plants seem to be drooping and curling. What should be done at that midday point? Water them or wait for the evening?

This post was edited by saood on Tue, Oct 1, 13 at 6:40

    Bookmark   October 1, 2013 at 1:12AM
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Oxboy555(Las Vegas)

Probably ok with the newspaper. No experience with that though.

Water them immediately if you're sure they're wilting from thirst. No reason to wait.

If you know it's about time to water and it's going to be a hot day, I'd water them in the a.m. to keep them hydrated through the rough daytime heat. Otherwise, I don't think it matters much for potted plants.

    Bookmark   October 1, 2013 at 1:00PM
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