Soils 101: Ammending clay soils

If you took a look to our past article on this series on the basic workings of soils, and if you lingered for a while on the soil composition triangle (or pyramid, if you will), you probably noticed that a good area of it falls under the category of plain old ‘clay’. That basically means, to put it simply, that the presence of clay is more impactful in how your soil feels and in what it can actually grow than sand or silt. Take a look at the pyramid again, and you’ll notice that any soil with over 55% of clay is automatically a clay soil, whereas it takes over 80% of sand or silt content in a soil to make it sandy or silty.

Knowing this, it is no wonder that the soils that most need remediation to turn into fertile, living soils that are sources of plant food (organic plant food, mind you!) are often clay soils, and that’s what this entry is going to be about. Now, the first thing to understand is that soil remediation always boils down to two things: increasing the amount of organic matter, and getting living things to actually colonize the soil. The question is really how you do that, without spending a ton of money on bringing a literal ton (or more) of organic material into your piece of land. This is where things get complicated.

If you have a forested soil which you are going to clear up, the short-term method to allow you to plant vegetables that same year would be to use the logs and branches, which you definitely are going to have around, with hügelkultur garden beds. You can see more about them here. These consist in basically a pile of logs covered with several layers of alternatively ‘green’ (leaves, tender stems) and ‘brown’ (dried leaves, woodchips) organic material, topped with actual soil. These structures end up producing a whole mountain of plant food on which you can begin to cultivate vegetables after one or two years. In the end, it should look like this:

Alternatively, you might want to go all the way into the soil and try a long-term amendment, which would consist in passing all the wood through a woodchipper, and then composting these woodchips with the assistance of a fungus (Stropharia rugosoannulata). You could compost it in place alongside the leaves, by making big mountains of it, or you could also try to directly work it into the soil. This last method would be theoretically the most short-term one as well, but that would be assuming that you had enough organic matter already decomposed (such as compost) to introduce in the soil. As woodchips are ‘raw’, you would have to wait around a year to plant after they have decayed.

Now, if you have a meadow or an otherwise open space, your best shot is to buy a mix of seeds of cover crop species (think at least one species of legume, and one of grass or grains), and plant it over the heavy clay soil. As it grows, you could either let it go to seed and colonize the soil, or cut it and alternatively let it decompose over it or mix it directly into the ground. In the meantime, you should begin colonizing any slopes or uneven spaces of the terrain with perennial plants (comfrey, or food plants such as elderberries) in order to prevent the topsoil that you are working so hard to make from washing away with the next rain. This is how many clay soils become that way, actually.

Whatever you do, don’t try to amend it with sand or silt! As the University of Illinois alerts, “it creates a soil structure akin to concrete”. Definitely not what we’re going after. Instead, you’re looking for a soil that routinely looks like this, before it becomes a full-fledged vegetable garden:

And if we take a closer look, we see that these people did. There's two distinct species involved, instead of just one massive cover crop monoculture:

This is all well and fine, but now you may be thinking: what about the second part of amending soil? Getting living thing to colonize the soil? Well, that’s already happening when you start any composting process, but there is certainly a lot that you can do to help the existing colonies of microbes and build up a soil ecosystem. Why not check our other articles on soil biology to understand how, as well as products like our Add Life organic fertiliser, which gives a boost to the colonies of both beneficial bacteria and fungi in your soil? Be sure to check both things out, so you can fully know that you are in the right path to improving your soil. And happy growing!

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