Clay Soils Hold Water & Sandy Soils Drain Easily. So Adding Sand To Clay Soils Ought to Help. But Does It In Reality? Here’s My Answer To Adding Sand To Clay Soils.
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There isn’t just one myth here. There are several. Plus a few bits of truth mixed in.
Let’s get the first myth out of the way. A lot of sites say that adding sand to clay soils means the clay aggregates around the sand and sets like concrete. And it could be right if we consider that concrete has sand in it. But of course it doesn’t have clay in it. And it has cement powder. So the two are totally different and adding sand to clay doesn’t mean it will set like concrete.
But of course if you spend ages mixing the two and are standing on the clay. Or digging it when its wet, you are going to smear it and it will set like concrete. But it’s nothing to do with the sand.
But logically if we add enough sand to clay it will open up the clay and not be so sticky. It’ll allow air spaces to form and the mix will drain better. And if it’s largely a sand mmix with some clay it could eventually become a reasonable soil.
But that means you need more sand than clay and that’s never going to happen on a garden scale. You’ll need lorry loads of sand and heavy moving equipment.
Deep Clay: Adding Sand To Clay Soils
The other problem is when your soil is deep clay. You’d need to mix the sand in through the whole soil profile.
Let me explain it this way. Imagine a large block of clay. One that goes a couple of metres down. Say we added pure sand on top. What would happen when it rained or we added water?
Simple. the water would drain through the sand and sit on top of the largely impervious clay soil. OK, some of it might drain sideways but where’s it going to go if your garden is all clay. It can only run downhill, it’s not going to drain into the clay soil.
And what if your garden is in valley. Or even in a slight depression. There’s nowhere for the soil to drain.
Soakaways: An Adding Sand To Clay Soils Solution?
A lot of people claim the easy way to drain a clay soil is to dig a soakaway. Or to dig deep holes and fill them with sand and bricks.
Well if you have a shallow clay cap on an otherwise free dining soil that might well work. But must clay soils are quite deep.
For example my grandfather’s garden and 5 acre orchard was next to a a clay quarry. Each day they dug deeper and deeper in to the ground and excavated thousands of trims of clay each week to make bricks.
The clay went down hundreds of feet.
There is no way you can dig a soak away deep enough to drain these soils. The clay is largely impervious and no amount of sand is going to make the slightest difference.
How Adding Sand To Clay Soils Might Work.
If you have a container of heavy clay, or a raised bed of clay, you might be able to add enough sand to make a difference.
But I’d suggest you actually add organic matter as well. Or only organic matter come to that. The organic matter will certainly benefit the clay and start it forming a more stable clay soil structure. Because clay isn’t bad. It is actually some of the most fertile soil available. It just needs handling correctly so that it can have amore open porous structure and allow the plants to grow.
I don’t agree with all the RHS recommend regards clay soils but their page is worth a read. I certainly advice considering No Dig on clay soils.