Clay soil: compost is better than sand

clay in soil
You can see streaks of clay in this clump of garden soil, but the addition of compost and other organic matter is breaking it up. Photo by Connie Oswald Stofko

by Connie Oswald Stofko

When you have clay soil, should you add compost or sand?

Compost.

“In the long run, by far, the best thing you could possibly add is organic matter,” said John Farfaglia, extension educator with Cornell Cooperative Extension in Niagara County. Organic matter can be compost, autumn leaves, peat moss or other plant material.

Organic matter is better because you have to add so much sand to loosen the clay, it’s not practical, Farfaglia said.

I asked this question because a reader left a comment on a previous article talking about the value of adding sand to clay soil. In a garden that is 16 by 45 feet, he said he added four tons of sand.

Another reason to use organic matter is that it improves your soil in ways that sand doesn’t, Farfaglia said. Organic matter gives your soil better texture and supports organisms such as earth worms and microorganisms that are beneficial to plants.

You can add organic matter to your soil at this time of year. Tip: If your garden is still wet, give it a few days to dry out. If you try to work with the soil when it’s wet, you can damage the soil structure. If you pick up soil in your hand and you can crumble it, you can work with it. If it sticks together, it’s too wet.

To break up the clay, try to incorporate your organic matter into the top few inches of your soil where the roots of your plant will be, he said. That will have a faster effect.

If you can’t do that, you can still top dress compost or organic matter on top of the soil. That will help.

You will need to add organic matter over a number of years, he noted.

14 Comments on “Clay soil: compost is better than sand

  1. Sand has to be dredged from other locations and as more societies use larger amounts of concrete, use of this resource is beginning to be a concern. Compost is a renewable that can be made on site, saving landfill space and transportation issues.

  2. Another reason not to use sand is it tends to “concretize” the clay which is the opposite of the effect you want. Compost is always the best solution.

  3. Compost can be bought at most big box stores and nurseries that sell garden supplies like soil. Also if you google: compost delivery there are a few local companies that will deliver large supplies of compost and top soil.

  4. There was a question about adding sand so I did some research on adding sand to clay soil. I mentioned it was old school and that seems to be the case. Adding sand to clay can make the soil more workable however it does not add any nutrients. When too much sand is added the soil becomes harder to dig which is where the turning to “concrete” comes from. That’s why compost is the best alternative for clay. It breaks up the clay as well as adds nutrients to the soil.

  5. Maybe we don’t agree on what clay is. If I want to dig a post hole in my yard where sand has not been added, I can dig down about six inches, and then I hit the clay, and I can spend two hours chipping away at it to get it two feet deep. So, I learned, I dig the six inches, fill the hole with water, wait ten minutes, dig four inches easily, hit clay, repeat until you can put in a post.

    Try this simple test. Get a five gallon bucket, fill it 1/3rd with clay. Now add sand, 1/3rd of a bucket of sand. Is it easier or harder to dig? Did it turn to concrete? NO. Fill it to the top with sand. Is it easier or harder to dig? Did it turn to concrete? NO! And it NEVER will!

    Now, I agree, organic material is essential. And if you want to wait forever to get friable soil, just add all the organic material you can get, year after year and you will learn patience. Or, add sand FIRST, then all the organic material you can get, and have a bountiful garden the first year! And better every year after.

    I have done it both ways.

    Just add sand to a 2 foot X 2 foot section of your garden. Dig it in, mix it with the clay, and see for yourself! If you get concrete, apply for a patent.

  6. One further note on soil improvement, that is simply magic. MUCH better than compost, and far cheaper. First, incorporate sand (if you have clay). Then, in the fall, cover the entire garden with four to six inches of wood chips. Ideally, for quick results, chips from green wood, that is with lots of green leaves. These are carbon neutral, that is, they will not rob nitrogen from your soil as they self compost. You can get them for free from tree trimming companies.

    In two weeks or less, rake some chips back, and be amazed at the hundreds of red worms working the soil just under the chips. Leave the garden covered all winter, then in the spring, just rake back the chips from your rows, no need to turn the soil, plant your seeds in the new black soil nature has produced for you.

  7. Connie, your question was not the best question for this subject. You asked, “When you have clay soil, should you add compost OR sand?”

    To THAT question, my answer would also be. “Compost.”

    But, notice that John ended with, “You will need to add organic matter over a number of years, he noted.”

    That is true no matter what you do! You need to incorporate organic matter as long as you garden.

    The difference is that if you add sand, you don’t have to wait a number of years to get good results. It was my bad that I did not make clear that no matter what you do, the soil needs, requires, MUST have, organic material.

    The better question might have been, “To get the quickest and most lasting results, should sand be added to clay soil?”

    My answer would be that if you add sand, you IMMEDIATELY make the soil workable, so that water and roots can penetrate, and you will notice an immediate difference!

    And, it is a ONE-time action. After that, organic matter will improve your soil like nothing else, and it is not necessary to ever add more sand unless your soil is still too heavy on the clay side.

    Sorry I made so many assumptions about what people would understand about my experience.

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