Clay Soil
by Doug
(in the garden)
Clay Soil
When we're talking about improving our clay soil gardens, there's one thing we have to understand first. And that is how soils are structured.
Soil Structure Does Not Equal Soil Fertility
The soil structure is the basic underlying mineral component of our soil, the parent material that includes ground up minerals - sand, silt and clay.
Organic matter is also a minor part (in terms of percentage of material) of the soil structure and we’ll talk about this in more depth later.
A minor point but an interesting one is that your top soil isn’t necessarily connected to your underlying rock material. For example, the top soil in the Mid-west is often composed of soil that was blown in (called loess). Soil can accumulate in different regions in different ways (including clay soil) but this isn’t the subject of this session. :-)
Sand
Sand particles are the 600-pound gorillas of the soil world. These are big guys (measuring .05 to 2 mm in size)
When we have a sandy soil, the big particles fit together with a lot of air spaces between them.
This allows several things to happen: water moves down through the sand quickly so drainage is fast and excellent (too excellent in sandy soils). Soil fertility also tends to be poor because the water tends to remove the fertilizer salts in it’s rapid downward progression.
Oxygen content is high and the space between particles is large; this lends itself to great root development but also high O2 levels can lead
to rapid consumption of organic matter.
So sand comes with the advantages of great drainage but poor fertility and water holding capacity. You can grow a good garden in a sandy soil but you have to apply a lot of water to do so.
Silt
Silt particles are the intermediate sized particles in the mix. They are .0002 to .05 mm in size.
They fit together a little tighter than sand so the drainage is not as good but water holding capacity is better. Air spaces aren’t as large
so root development isn’t as fast but between the water and the lack of available O2, fertility levels are higher than sand.
Silt soils are typically very productive garden soils.
Clay
Clay soil particles are tiny, measuring less than .0002 mm in size.
They pack together very tightly, water tends not to run out and drainage is poor.
Oxygen content is low and small roots have a tough time working their way through between the open areas.
On the other hand, fertility is good because the nutrients have nowhere to go.
Clay soil presents more gardening problems than the other two types because they are harder to fix.
Practical Garden Soils
Soils are a mix of all three components and the proportion of sand to silt to clay determines what kind of soil you have.
The higher the proportion of clay in the mix, the worse your garden soil is going to be.
Generally, when clay starts to rise above the 30 percent mark, we start noticing it.
When it rises over the 40 percent mark, we know we have clay and over 50 percent, we don’t have clay - we have trouble.
At 60 percent clay, we have pottery (give or take a bit)
So What’s This Mean?
Practically speaking for the home gardener, it depends. If you have a slight clay problem, you can amend it and make it a very fertile soil.
Or, you can handle the problems by cultivating and managing the soil properly.
If you have a serious clay problem, then we’re looking at some other serious solutions. And those will be dealt with in the next few posts.
What is important in this post about your clay soil is that you understand exactly what you're dealing with before you launch yourself into some form of garden-torture.
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