Garden Myths Gardening Soil

Garden Myth: Add Sand to Lighten Clay Soil

Wheelbarrow of sand on top of red clay soil, with question marks indicating doubt.

Contrary to popular belief, adding sand to a clay soil will not lighten it. In fact, it will make it even harder to work! Ill.: milyhandyman.com & hiclipart.com

You often hear that the solution to a heavy clay soil—one that is hard to work, takes forever to dry out in the spring, then cracks and stays impossibly parched when it does finally dry out—is to add sand. And the idea seems to make sense. After all, if clay is so dense and heavy, letting water and air circulate with only the greatest difficulty, it’s because it is composed of extremely fine particles that pack tightly together. What could be better than to add sand, whose particles are huge in comparison. Wouldn’t the presence of large sand particles mixed in among the finer clay particles allow water and air to circulate freely?

Clay plus sand equals cement
Adding sand to clay soil actually gives it a consistency more like cement than garden soil. Photo: motherearthnews.com, cdeasia.com & patrickmorin.com

But that’s not how soils work. Add sand to clay and the clay particles will just pack in again all around the sand, creating a mix that turns rock-hard, more like cement than garden soil.

Shovel filled with organic matter.
It’s organic matter you need to add to clay soil to lighten it. Photo: bhg.com

Instead, to lighten clay soil, the real solution is to mix in a lot of organic matter: 2, 4 or 6 inches (5, 10 or 15 cm) or more of leaf mold, fragmented wood chips, chopped leaves, forest mulch, compost, manure, etc. The humus resulting from the decomposition of organic matter will cause the clay particles to agglomerate, leaving space for air and water to circulate and making the soil lighter and easier to dig.

And you’ll want to continue adding organic matter regularly because organic matter, by its very nature, decomposes and disappears over time. However, once you’ve laboriously mixed in the first load of organic matter in order to lighten the soil, it will be much simpler to maintain the soil’s new lighter nature. You only have to apply the matter to the surface of the soil, as a mulch, since the humus resulting from the mulch’s decomposition will naturally work its way down into soil below.

The Laidback Gardener’s Method

Illustration of soil layers: top soil, subsoil and bedrock
Add a layer of top soil over the clay subsoil and gardening will suddenly be simple! Ill.: US Department of Agriculture

Or do things the laidback way. Rather than go through all the effort of trying to mix organic matter into lumpy, heavy clay that is not going to readily mix with anything, simply add a thick layer (8–12 inches/20–30 cm) of good garden soil (topsoil) directly over the clay … and from now on, garden only in this new layer of topsoil.

You see, while clay makes a very poor surface soil, it is an excellent subsoil, holding on to moisture and minerals and releasing them to the plants above as needed. With a layer of good soil over a clay subsoil, you just created an environment resembling the very best agricultural land.

In fact, most likely you will have recreated the original conditions of your own yard, the way things were before the house was built. That’s because, in a typical housing development, the first thing that the builder does is to remove and sell the topsoil (it will be used among others in preparing commercial garden soils), leaving a field of clay soil in which plants will struggle to grow. Of course, just before the house goes on sale, the contractor covers the clay with a layer of nice green sod to make the home more readily saleable. So, if you reinstall a good layer of quality soil, you’ll actually be restoring the proper order of things … and making all your future garden efforts easier!

Based on an article originally published in this blog on November 27, 2015.

Larry Hodgson is one of Canada’s best-known garden communicators. He has notably been editor-in-chief of HousePlant Magazine, Fleurs, Plantes et Jardins, À Fleur de Pot and Houseplant Forum magazines and is currently the garden correspondent for Le Soleil and radio garden commentator for CKIA-FM Radio. He has written for many garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening and Organic Gardening. He also speaks frequently to horticultural groups throughout Canada and the U.S. His book credits include The Garden Lover’s Guide to Canada, Complete Guide to Houseplants, Making the Most of Shade, Perennials for Every Purpose, Annuals for Every Purpose, and Houseplants for Dummies, as well as nearly 60 other titles in English and French. He is a past president of the Garden Writers Association (now Garden Communicators International) and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. He resides in Quebec City, Quebec, Canada.

7 comments on “Garden Myth: Add Sand to Lighten Clay Soil

  1. There was farmer in the redhills of South Carolina, who was nicknamed”the OnionMan”.
    He bought chicken manure when no one really wanted it &covered his field & turned it under.
    His red soil became black & he grew the best onions in the state.

  2. In addition, if it’s suitable to do so, I would do this: sow soil-building annual cover crops that can be winter-killed or mowed/cut back before going to seed, and let them slowly loosen compacted soil, prevent erosion, attract insects and beneficial microbes, rebuild mycorrhizal communities, etc. Some call it “green manure.” Now that’s laid-back!

  3. I actually worked with so-called ‘professionals’ who believed this myth!
    The soil in the Santa Clara Valley happens to be excellent. Seriously, it is one of the best places on Earth for gardening. That is why there used to be so many orchards here. Yet, there are some who do not believe it. I am offended when someone tells me how bad the soil is. The truth is that they do not know how to work with it.

  4. Dave in Edmonton

    well I think you just saved me enough money to buy seeds for another couple of years. I put sand on the veggie patch a few years ago, very light touch ~1/4 in, and it seemed to help, so I planed to lay a solid inch and roto till it in with some compost. I read your bit, and thought I should get a 2nd opinion. sure enough, from U Sask (they know stuff!!!) say the same, link:
    https://gardening.usask.ca/article-list-soils/misconception-adding-sand-to-clay-soils.php
    interesting they also say not to till, ever. The family has had this garden patch for a few months over 50 years, and have always added compost, mostly leaves, grass clippings and non edible veggie plane parts, and it is still hard to work. But we have also always grabbed a garden fork in the fall, and by hand turned over the entire patch, burying the organic stuff. A rough till, leaving big lumps to catch snow for extra ground water. there should really be no shortage of organic “stuff”. In fact, the height of the top of the soil, compared to the adjoining side walk is a good 3 to 4 inches higher than when we bought the place.
    Anyway, will become laid-back, and not turn it over for a couple of years, and just dump the compost on top
    the key is, we have also been growing veggies there for 50 years, and the soil, such as it is, has always produced good crops, weather permitting.

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