Options for Dealing with Clay Soils

by Doug
(in my garden)

When it comes to clay soil gardening and actually getting something done about it, you have several options. These are solutions recommended throughout the gardening literature; I don’t expect you to agree with each of these or be happy with the findings but I’m just trying to give you honest, realistic answers.

Raised Bed Gardening

You got it. Ignore the clay soil, build raised beds at least 12-inches tall, fill ‘em with decent top soil you can work with and move on with your gardening life.

The upside to doing this is that you get something decent without a lot of messing about and you can design interesting gardens depending on the shapes of your beds.

The downside is that it’s slightly more expensive than some of the other remedies in that you have construction costs involved.

This is the solution we’ll be using in our new garden because of shallow top soil and clay where there is topsoil. Instead of doing a lot or remedial work, I’m just sucking up the building-costs as not much more than having my alternative (dig, remove and replace) and moving on with actual gardening. In my world, this is far less stressful and guarantees me a good garden as fast as I can build beds. I’ll be posting pics on this all this summer.

Altering the Clay

Now, we get to the interesting options:

Digging and Replacing.

It is often recommended that you dig out the clay, and substitute with decent soils. This is sometimes (thankfully less and less) recommended for the actual planting holes (more on planting coming in next lessons) but often for the entire bed.

In short, it depends on how heavy your clay soil is (how much clay in the mix - see previous posts). If a very heavy clay, then your excavation creates a hollow in the clay, a bathtub as it were. This is not a problem in a dry year but a wet year is going to give you a serious bathtub effect where your plants are going to require swimming lessons.

A lighter clay soil where the drainage is only slow - not non-existent - will be fine with excavation.

Double digging

Double digging works for many mild to medium clay soils because you’re creating a decent top soil with good drainage and you have slow drainage under that. You may have transient drainage problems in the early spring or flooding conditions but they shouldn’t stick around long enough to be a serious problem.

Again, double digging on heavy clay soils is the same as dig and replace except it is a lot more work than having a tractor dig out the clay.

Adding Compost and Organic Matter

This is going to improve most soils. At least to the level that the organic matter is mixed into the soil.

Organic matter (compost, peat moss, coir, whatever) will help to separate the small clay particles and aids drainage as well as providing some extra nutrition for plants.

Organic matter decomposes - figure half of what you put on in year one is gone at the start of year two. And half again by the start of year three. Half the remaining organic matter disappears every year. This is why you pretty much have to add organic matter every year to any soil if you want the full benefits.

The warmer your garden, the more organic matter is consumed every year. So while those of us in a USDA zone 4 garden will likely only lose half in any given gardening season, I’d be surprised if there’s much left in a Southern USDA zone 8 with the long growing season and high soil temperatures.

Adding Sand

Adding sand to clay is sometimes recommended as another more permanent method of separating clay particles and allowing drainage.

This works in small doses on small gardens but it’s big time labor and time consuming. You can only add a very, very small amount of sand in any given year (likely less than 1/2 inch) or you wind up with chunks of clay mixed into chunks of sand. And the sand has to be thoroughly mixed into the clay soil.


So - it’s very much like double digging and adding a tiny bit of clay to the mixed soil as you dig. Simply tilling it in isn’t going to really work well in my experience. The tiller doesn’t get down very far, you create a hardpan layer right under the tilling and unless you till at exactly the right time, you’re almost guaranteed to create chunks of clay interspersed with sand.

Finally, this is something you might try with a light clay soil but it will be very difficult to accomplish anything with a heavy clay soil.

I confess this is a change in my overall thinking about adding clay. I used to think it would be easier to do this.

Soil Drainage

Heavy clay soils and poor drainage seem to go hand in hand more often than not. And this spells disaster for many gardeners. Some think that raising the level of soil will somehow solve this. What raising the soil does is put a thin layer of decent soil over top of the heavy clay and while drainage is good in the top inch or so, it gets very bad under that (where the roots are) and not much changes. That is, unless you add a 8-12 inches of top soil (like a raised bed) and ignore the drainage.

Otherwise, to get rid of excess water, you have to either slope your land towards the drainage direction (helping surface water run towards the drainage - away from your garden) or dig and install drainage tile to a bottomless cistern in the low section of your garden. Both are expensive but necessary if you really want to remove water.

Soil Additives

Sprays

There are some additives (miracle cures) advertised on the Net and these tend to fall into the range of industrial de-greasers. They make water slippery and aid drainage in this way. They do not change the structure of the soil nor can they in any way be considered organic practices.

So I’m not even going to recommend them for any kind of clay soil.

Gypsum

You’re going to read all about gypsum and clay soil everywhere on the Net. It’s one of the most common of gardening myths that this is the cure-all for all manner of clay soil problems.

Well, the reality is that it isn’t.

I’m going to be writing an entire article in this series on gypsum and clay soils but the gist of that article is that it depends on your soil.

If you have a limestone based soil - then gypsum won’t work. If your soil already contains enough calcium, gypsum won’t work. It might work on soils that don’t fill those criteria. But I’ll write more shortly on this.

Moving

Now, if you’re a serious gardener and you find yourself on a bit of property that is heavy clay - and you want a very, very large estate garden, then move.

I know, that’s not what you wanted to hear. You wanted me to tell you the magic secret of having huge gardens without a lot of effort. You wanted that magic bullet that would let you have great soils. Well the hard reality that I and a bunch of you are facing is that there are no easy answers. There are no magic bullets.
The answers are above (or move your house).

Techniques to Live with Clay

There are some techniques of planting and gardening you might find useful as well as plants that handle clay soils but that’s as good as it gets. Those are coming up.


Me? I’m building raised beds. Lots of raised beds. Big gardens! Big raised beds. :-)