Suitable soils for the Walstad method - El Natural - Aquatic Plant Central

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El Natural Diana Walstad's low-maintenance, soil-based 'El Natural' method for keeping plants and fish.

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Old 07-29-2012, 09:49 AM   #1 (permalink)
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Default Suitable soils for the Walstad method

“In general, aquatic plants seem to do well in a variety of soils—clays or loam soils with some organic matter. Indeed, I haven’t been able to find any major or consistent difference in plant growth in various ordinary soils. . . . In most instances, substrate fertilization appeared to be either detrimental or not helpful. Best plant growth (under aquarium conditions) often appears to be not in the most fertile soil, but in the one that is the least toxic.” Ecology of the Planted Aquarium, p 132.

So many people ask questions about which soils are suitable for use Walstad aquaria, it seemed time to start a thread on just that topic. Here is where we can share our results using different soil substrates.

First, some definitions. “Soil” has different meanings to different people. For our purposes, “soil” means any growing medium intended for terrestrial plants, but which we have adapted for use in the planted aquarium. “Topsoil” has a very specific meaning to soil scientists, horticulturists, and geologists. Often, what is labeled “topsoil” in a bag in your garden center bears no resemblance to natural topsoil as understood by science. Most natural topsoil is primarily minerals, with only a small percentage of organic matter. In our discussion, we should use the general term topsoil to refer to naturally occurring surface soil. When we are talking about a specific commercial product that has “topsoil” as part of its name, we should be sure that is understood.

Another term that needs definition is “organic”. In this discussion, organic is used in the scientific or chemical sense; that is, material derived from living matter. This organic matter will be in various stages of decomposition. When I use the term “organic” I am not referring to the organic method of gardening, and I most definitely do not mean the undefined marketing hype used to sell so-called “natural” products.

And one last bit of clarification, when we talk about soil in this discussion, we are not referring commercial brands of aquarium substrates, like Flourite, Eco Complete, ADA Aquasoil, etc. Some of these products are very good, and may be useful in the Walstad method. Some are not.

I will start the discussion in the next post. But the only way that this thread can become really useful is if you post your knowledge, experience, and questions too!
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Old 07-29-2012, 09:57 AM   #2 (permalink)
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Default Re: Suitable soils for the Walstad method

Miracle Gro Organic Choice Potting Mix (MGOC) is often recommended, and by Diana Walstad herself in her on-line article about small aquaria for shrimp at http://www.atlasbooks.com/marktplc/00388Shrimp.pdf. Unlike many other “potting soils”, MGOC has a clear list of ingredients and a nutritional analysis on the bag:

50-55% composted bark
Sphagnum peat moss
Pasteurized poultry litter
“organic wetting agent” (whatever that is)

Analysis 0.10-0.05-0.05
total nitrogen 0.10%
available phosphate (P2O2) 0.05%
soluble potash (K2O) 0.05%
". . .feeds up to 2 months. . ."

This tells us several important things. First, this product is 100% organic matter. Remember, natural soils are almost never 100% organic matter—less than 20% is more common. So this soil is going to undergo a lot of decomposition in the aquarium.

Second, it has chicken manure in it, which makes it much more fertile (higher nutrient level) than most other potting mixes. But, these nutrients come from slow-release organic sources, not synthetic inorganic chemicals. Not that there is necessarily anything wrong with synthetic fertilizers, but they behave differently when submerged than organic ones do. This higher fertility is expressed in the analysis (which shows much more nutrients than typical for potting mixes or natural soils) and the last statement, “feeds up to 2 months”.

What does MGOC look like when you open the bag? It is dark brown, with a mix of fine particles and some pretty big chunks of not-yet fully decomposed bark. These chunks are a source of concern, for several reasons discussed below. I did a quick test with a ¼” soil sieve, and about 20 to 25% of MGOC will not go through the sieve, even after rubbing it hard with a gloved hand.

MGOC has three major advantages:
1. It is a nationally available product
2. The ingredients and analysis are clearly listed on the bag
3. It is relatively consistent no matter where you buy it. (Many other products vary greatly from one region to another.)

Used straight from the bag, MGOC has four major disadvantages:
1. The big pieces and many of the smaller pieces float, which can make a big mess if your cap is not heavy enough, or if you change your mind and move a plant.
2. The high nutrient content usually causes an ammonia spike in the first month following tank set-up.
3. The partially decomposed bark releases a lot of tannins into the water. This is not usually harmful to fish or plants, but the tea-colored water may look bad to you.
4. Because it is 100% organic matter, if the soil and/or cap is too deep, the soil layer may become very anaerobic. This is bad for many reasons.

Fortunately, there are easy ways to deal with all of these disadvantages.

The simplest ways are a thin soil layer, patience, and water changes. This soil is hot stuff, you do not need much! How deep a soil layer to use depends on size of tank and types of plants, but I would never use more than 1.5”. For beginners and small tanks, 1” or less is plenty. Patience is necessary to allow the biological filter to develop properly and absorb the ammonia. Water changes help with that, and also remove the tannins. Eventually the big pieces become saturated with water and no longer float.

The more sophisticated ways to deal with these problems involve processing MGOC in some way before you use it. A quick and effective process is “soak and drain”. Put the soil in a big bucket, cover it several inches with water, and stir well. Let it sit over night, then carefully pour off the floaters and the brown water. Fill, stir, and let sit over night again. Repeat the soaking and draining cycle until you see no floaters and the water is reasonably clear, or until you can’t wait any longer, LOL. Seriously, three complete cycles is usually enough to make a big difference. This method will result in a loss of total volume of soil of 25-30%, so start with more than you need for the tank.

Another way to process MGOC is to mineralize it. This process is described fully in several great threads in the library forum. Mineralization greatly speeds decay of organic matter into a very stable form called humus. Humus does not release ammonia into the water, and is unlikely to become anaerobic.

And there is one last tip for using MGOC or any other highly organic soil: mix it with an inorganic substrate that has a high cation exchange capacity (CEC). Examples are laterite, Flourite, Turface, plain cat litter (no perfume, antimicrobials, or clumping agents), and Safe-T-Sorb. Remember, natural soil is almost never pure organic matter. Mixing the organic matter with inorganic high CEC substances means that the ammonia and other nutrients produced are held in the substrate where plant roots can use them, but where they will not harm fish. And by reducing the percentage of organic matter, you reduce the likelihood of the soil becoming anaerobic. I like a 50/50 mix. Phil Edwards first gave me this advice, and it has worked well for me.

Let's hear from eveyone else! What kinds of soil have you used in your Walstad tanks, and how well did they work?
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Old 07-29-2012, 05:51 PM   #3 (permalink)
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Default Re: Suitable soils for the Walstad method

this is what i usually do. soak the soil, let it get sedimented over time (not so long perhaps 12 hours) than we will get the floaters which usually wood peat. throw the wood peat. and than drain the water to the level of the soil. and than take a gulb of this wet soil cover it entirely by a piece of napkin, than compress it with hands. it will form a toy clay like material, and when it is used in tank usually it will mess the water very minimal. i dont know if this method will make anaerobic condition or not (because we compress it i think it will be more difficult for the soil to get aerated) but so far i have 3 tanks setted up with this method, and all of them have a good growth. i also add a little clay for this soil like 1:7 ratio
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Old 07-29-2012, 06:00 PM   #4 (permalink)
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Default Re: Suitable soils for the Walstad method

Compressing the soil with a cloth will not cause it to become anaerobic--you are probably just squeezing out the excess water.

Adding the clay has the same effect as mixing with an inorganc high CEC substrate. Most of these are just fancy forms of clay. And the mineralized topsoil (MTS) process includes adding clay if the soil doesn't have enough to begin with.

Thanks for sharing your method. What kind of soil are you starting with?
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Old 07-30-2012, 07:46 AM   #5 (permalink)
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Default Re: Suitable soils for the Walstad method

Thank you Michael for taking time to post this! Awesome,thank you! I'm definitely going to try the 50/50 mix!
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Old 07-30-2012, 08:20 AM   #6 (permalink)
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Default Re: Suitable soils for the Walstad method

You're welcome, please let us know how the mix works for you.
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Old 07-31-2012, 02:57 AM   #7 (permalink)
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Default Re: Suitable soils for the Walstad method

Quote:
Originally Posted by Michael View Post
Compressing the soil with a cloth will not cause it to become anaerobic--you are probably just squeezing out the excess water.

Adding the clay has the same effect as mixing with an inorganc high CEC substrate. Most of these are just fancy forms of clay. And the mineralized topsoil (MTS) process includes adding clay if the soil doesn't have enough to begin with.

Thanks for sharing your method. What kind of soil are you starting with?
in indonesia it is way more easier to get a "home made" top soil than getting the branded one. for 50 cent u can get 10 kg of it. but usually they use cow dung for the fertilizer. so usually i use the soil in my garden first for like about 6 month before i use it for my tank
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Old 07-31-2012, 05:14 AM   #8 (permalink)
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Default Re: Suitable soils for the Walstad method

That is a good idea for any soil treated with fresh manure or that may be loaded with too many nutrients.
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Old 08-01-2012, 02:21 PM   #9 (permalink)
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Default Re: Suitable soils for the Walstad method

Michael,

This is an ambitious thread! Thanks for starting it.

I've maintained "soil-based" tanks for at least 10 years, generally with some success. I use the cheapest bagged "top soil" that I can find. Then I "mineralize" it.

"Mineralization", in this context, means the conversion of the organics in the soil to minerals that are available to the plants, and in a form that doesn't lead to algae and other problems.

I mineralize the top soil by soaking it in a pail of water for a week or so, with several water changes. Unwanted material floats to the top and is easily removed. I rarely have any algae in new tanks, and when I do it is always BGA which often disappears on its own in a week or so.

My problem with MGOC is that it has too many organics, and as you noted, it can cause problems. I have a bag of it here and I'll use it eventually, but I'll mineralize it first and, after that is done, it should be about the same as the cheap bagged topsoil. So why bother with it?

(Diane can grow any plant anywhere with anything, so the rules that apply to most of us don't apply to her. )

If anyone disagrees with my definition of "mineralization" or anything else that I've said, I hope that they'll post their comments.

Bill
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Old 08-01-2012, 02:42 PM   #10 (permalink)
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Default Re: Suitable soils for the Walstad method

Bill, I agree that the 100% organic make-up of MGOC is the cause of most problems with using it. The added nutrients from the poultry manure just make it worse. Yet because it is so frequently recommended and widely available, I thought it best to start the thread using it as an example.

Recently I've used high-quality homemade compost from a neighbor, mineralized it, and have very good results. But I still mix it with Turface or Safe-T-Sorb so that the soil part of my substate is not 100% organic.

What brands of "topsoil" have you used, and where did you buy them?
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