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Mary Lowther column: Flocculation and other dirty chemical reactions

Regardless of soil type your compost will benefit enormously with the addition of clay.
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My garden soil. Most of the content settled out in the first two minutes and four hours later this is what it looks like. I have mostly sandy soil. (Mary Lowther photo)

By Mary Lowther

My grandmother used to tell me I should never listen to gossip and she was probably right, but that kind of limits polite conversation to the weather. Besides, Granny always followed that caution with an update on every member of the family and most of her neighbours as well, which sort of undermined her basic thesis.

Perhaps we should not listen to gossip, but we certainly should know our dirt. The kind of soil we have determines how we garden and what kind of fertilizer we should use. An easy way to find out is called “soil fractional analysis.” Simply dry a cup of soil and sift out the stones, put the soil into a two-cup jar and stick a piece of masking tape on the side from top to bottom. Fill the jar with water, leaving an inch of space at the top, add three drops of dish soap to soften the water and separate the soil particles. Put a tight lid on the jar and shake vigorously for several minutes, then place the jar in bright light so you can see the soil settle.

Two minutes after you stop shaking, mark the side at the level to which the soil has settled; this mark indicates the amount of sand particles in the soil. Two hours later, mark the top of where the level is now; this is the layer of silt. When the water has finally cleared, and this may take up to two weeks, measure this final layer and that indicates the amount of clay in the soil. If the water doesn’t ever clear, what you’ve got is mostly clay and all of our sympathy.

Most soils are mostly sand or clay with some silt. If you have clay soil, you might not want to use dolomite or dolopril because these both contain far too much magnesium (about 13 per cent). Magnesium tightens up clay, making it even more impervious to water, microorganisms, roots and your shovel. Use agricultural lime instead because it contains much less magnesium (less than two per cent).

Here’s Solomon’s suggested recipe for fertilizer for clay soils:

4 litres seed meal (I use alfalfa)

2 cups agricultural lime

2 cups agricultural gypsum

1 litre soft rock phosphate

2 tsp. borax

1 1/2 tsp. zinc sulphate

1 tsp. copper sulphate

1 cup kelp meal or azomite

Mix it all up and use at the rate of 4 litres per one hundred square feet of garden.

Gradually your soil should become more friable and easier to work with as the clay flocculates. I know that sounds risqué, but remember we are talking dirty here. Flocculation is a chemical reaction that occurs when lime meets clay, separating the molecules and aerating the soil. Clay soils can produce excellent crops because, when amalgamated with compost in worms’ guts, it turns into humus that will provide your soil with nutrients for many years.

Regardless of soil type your compost will benefit enormously with the addition of clay. Compost made with one to two per cent clay sprinkled into it will capture significantly more nitrogen. About one and a third buckets of clay spread into a four foot cubed compost heap should be enough. I make compost like this for my sandy soil, but I have to hunt down the clay.

If you make this in the fall and add Soft Rock Phosphate (SRP) to the mix, you’ll have an even better product because this makes the phosphorus far more available to plants. Solomon recommends adding one 50-pound bag of SRP to the same heap and this should create enough compost to cover 1,000 square feet. You won’t need to add SRP to the fertilizer mix then.

“That much Soft Rock Phosphate costs nearly 50 dollars!” I complained to David. He replied that most people spend more than that on their hobbies. Having heard the answer I wanted I discretely forgot to mention all the other expenses, such as coir, secateurs, hoses, timers, alfalfa meal, seeds and fertilizer ingredients. Growing top quality food doesn’t come cheap, but our health is worth it.

Besides, if David didn’t quibble at the cost of the land I grow food on he is unlikely to object to a few ancillary expenses. Why burden him with too much information?

Please contact mary_lowther@yahoo.ca with questions and suggestions since I need all the help I can get.