How to Improve Clay Soil

| 3/7/2014 9:40:00 AM

Tags: Vicki Mattern, clay soil, organic, compost,

I have heavy clay soil that becomes as hard as a brick when it dries, and my neighbors who also garden have asked me how to improve clay soil. What are the best methods for improving clay soil?

First, the good news: “Of the three major soil components — sand, silt and clay — clay has the highest nutrient content,” says Garn Wallace, president of Wallace Labs, a Improve Clay Soilsoil-testing firm in El Segundo, Calif. Clay soils retain minerals in forms that are readily available to plants and that aren’t water soluble, so rain and irrigation water are less likely to leach them away. The trouble is that clay lacks good porosity. Its fine-textured particles tend to clump tightly together. Air, water, roots and seedlings can have trouble moving through it, so crop yields may be lower. (Plus, clay is a pain to work in!)

Increasing your soil’s organic matter is the first and most important step toward improving heavy clay soil. Organic matter invites in more porosity-improving earthworms. Work in compost, grass clippings, shredded leaves or other organic materials. Plant and turn under cover crops, and safeguard your soil’s surface with an organic mulch to prevent crusting. Sand or peat moss can also improve soil texture, but they lack many of the other benefits of organic matter, such as beneficial microbial activity and nutrients for your plants to uptake. Plus, you’ll need a lot of sand to make a real difference (1 part sand to every 2 parts clay soil).

Photo by Dreamstime/Ian Nixon: Don’t be foiled by your heavy clay soil: Add organic matter to soften up your tough terrain.

Vicki Mattern is a contributing editor for MOTHER EARTH NEWS magazine, book editor and freelance magazine writer. She has edited or co-authored seven books on gardening, and lives and works from her home in northwestern Montana. You can find Vicki on .

4/4/2014 8:48:57 AM

I find sand even in highest ratios leaves you will cob or a bathtub of clay on all sides and a mess in the middle. I have tried gypsum with some good results, but ph problems. I now use organic amendments. I have a community garden that is like a parking lot. Tilled 8 hrs and only got 3" deep. I then made rows of clippings/leaves/ground tree mulch. Left it for a season and then tilled. Tiller ate the area up like hot butter. I find cover crops and lots of organic matter the best for clay soils. There is no magic wand and the soil may take a few years to get what you want, but that's why we garden, to slow down and enjoy.

Susan Berry
3/12/2014 8:29:36 AM

Very true. We have had clay soil to contend with for many years farming in NC and it is alot of work adding organic matter in the form of grass clippings, manure, cover crops, dried leaves, etc. But we have also had great production in our veggie crops. One thing I will advise, do not miss a year amending. It only takes one year of not organic matter to return to solid clay again. I know, I slacked off one year and was more work the following Spring. We added manure and cover crops in Spring tilling or turning this in. During the Summer we would mulch with grass clippings which ends up working in and is great for the soil then in Fall, which is when we did the majority of amending, we added Fall leaves, vegetable crop plant residue and manure. Plant one more Fall cover crop to till in right before Winter or over Winter and till in in Spring and you'll have amazing loam that doesn't even resemble clay.

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