Amending Clay Soil

soil compost mulch

by John Dromgoole

How can you improve clay soil for better drainage and plant health?

Pea gravel: Add about 3″ to the top of the soil and work it in to about 8-10″. This helps open up the soil.

Decomposed granite: You can screen this if you like. Add about 3″ and work into the soil to 8-10″. This also adds minerals to the soil. It can compact down (which is why it works so well as a mortar in flagstones & to make paths) so be sure to mix it in well.

Compost: You want to add this every time you plant, to help soil drainage and add nutrients and microbes to the soil. One of the goals in repairing heavy clay soil is to bring a lot of life to it, because the microorganisms that are in there will secrete a glue-like substance. And they live in the air, they really need some important air in there, they are not anaerobic organisms and so you really need to open it up. And that glue-like substance that they excrete binds the particles of clay together into a really nice tilth. So compost is an especially important addition. Work in new compost, too, every time you change out your vegetable garden.

Expanded shale (haydite): Texas A&M did a lot of research on this and the Dallas Arboretum has found it to be very effective in making the soil more porous. It’s a Texas product; it’s a little over 65 million years old. It’s been around here a long time and does not break down.

This is the stuff that’s been sitting around here since the end of the dinosaur age. This stuff was deposited in the soil when Texas was a huge lake. The next million years that you are gardening in that spot it’s going to drain very, very well.

You can also use to include in your succulent potting mix and to improve sandy soil.?
In a heavy clay soil it will provide the drainage and in a sandy soil it will hold moisture. I understand it’s nearly thirty-eight percent of the weight of each stone here in moisture.

Soil activators: There are many out there that feed the microorganisms in the soil. Two are Lady Bug Terra Tonic and Medina Molasses for Plants, Turf, and Soil.