Options for Gardening on Clay Soils
by Doug
(in my garden)
Remember that all remedies are pretty much mechanical because what we’re trying to do is separate the tiny clay particles, allow air and root movement between them and eliminate some of the water problems in this kind of soil.
I also note that heavy clays soils (50% clay particles or greater) will have different characteristics and require different “fixes” than soils with less of a percentage of clay.
One problem brought up by at least one member is the existence of multiple layers of soil and clay. You have a slightly clay soil over top of a heavy clay layer. Or, with really poor garden-soil practices you’ve created this layer by repeated scuffing or polishing of that soil layer with roto-tiller tines (tilling at the wrong time when the soil is too damp). Tillers compress this lower level and make it impenetrable. Again, this demands a different response.
The Single Solution That Works in All Cases
No matter what your problem, building good raised beds will work. And it will make your garden life ever so much easier. Mayo and I, with our shallow soil, are constructing raised beds throughout our garden; it’s the only way we can successfully garden on this property.
So, if you have some really serious problems (see below) the cheapest solution is often to build raised beds.
The Second Solution That A Lot of Folks Use
Excavate. Remove clay. Replace with good soil. Do this at least 18-24 inches deep for perennial and vegetable house-gardens.
Way Too Much Water = Drainage
If you have a soil that collects and holds too much water, then the time-honored way to eliminate that water is to install a drain system in your garden.
On the home scale system, this involves excavating a large hole that will hold a bottomless tank. The size of this tank depends on the size of the area being drained but it has to be large enough to handle a fast inflow of spring runoff and mid-summer downpours. Drainage tiles are run through the garden and hooked up to the bottomless tank. Water flows downward so excess water drains into the tank where it slowly leaks out the bottom. This slow speed is why the holding tank has to be calculated to be able to hold enough water to handle the inflow during heavy draining periods.
Normally we suggest landscapers install this kind of system, they’ll have the tools and expertise to both calculate and install this.
Farmers have used drainage systems for centuries to bring heavy clay fields into production; it is a remedy on the home front as well.
Adding Organic Matter
Organic matter in the form of compost (or other material) is a great way to break up lighter clay soils. Incorporating this material separates the small clay particles and helps feed the plants.
Do understand that organic matter is consumed in northern soils at roughly one half of the existing level per year. So if you add 2 cubic feet of peat in year one - you’ll have one cubic feet left of peat at the start of year 2. In the South, this is even faster because of the longer season and heat levels; organic matter can completely disappear in the year it is applied.
So you have to add compost every year if you want to see continued success.
Adding Sand
Using a mechanical addition such as sand can be done but it is fraught with potential danger.
I generally say if you think you want to add sand, do it one quarter to one half inch at a time (per year) and work it in thoroughly. If you add too much or don’t mix it thoroughly, you wind up with patches of sandy soil interspersed with balls of clay - or clay soils with streams of sand running through it. Either way, you won’t be happy.
In general, I’m not convinced this really works.
Double Digging
This works really well. I’ve done it for years. Some organic gardeners now say it “doesn’t work”. It works fine. What started this notion was the thought that fungal strands get chopped up when you till or dig; and no-till, no-dig is all the rage to keep fungal strands intact. For the most part, I agree with this because I’m a lazy gardener. I have done this for years in some of my gardens.
But when it comes to maximizing production and actually creating a soil that will grow carrots properly, you’re going to need something that’s a lot more open and loose than clay soil. Double dig it - work in scads of organic matter and you might be able to actually grow great carrots.
If you’re growing great root crops, you don’t have heavy clay soils.
The downside is that organic matter disappears very quickly and your soil will revert equally fast.
Gypsum
Ah, here’s where we run headlong into one of the garden world’s most endearing myths. I’m going to have to devote an entire post to telling you why this is not necessarily a great idea depending on the nature of your soil. It’s coming.
Bottom Lines
So when you get a sense of how to test your soil for clay content to arrive at the percentage of clay in your soil (coming) then you’ll have a sense of the extent of the work you’ll have to do.
The heavier the clay, the more work it is to fix it.
And that’s about the extent of it.
Raised beds
Excavation
Drainage
Organic Matter
Sand
Gypsum
Double Digging
So What's the Bottom Line
As we'll see when we get to gypsum, there is no one size fits all kind of answer. It depends on your soil - and your pocketbook - and your determination in the way you want to garden.
This means you have to understand your soil (coming) and figure out your personal response to this information with some help from your local sources.
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