Garden Myths Gardening Laidback Gardener Tip of the Day

Gardening Myth: Adding Sand Will Lighten Clay Soil

20151127AYou 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 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 then 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?

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.

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, 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 to add organic matter regularly because organic matter, by its 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 descend into soil below.

The Laidback Gardener’s Method

Add a layer of top soil over the clay subsoil and gardening will suddenly be simple!

Or let the laidback gardener inside you out. 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 to 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 re-install a good layer of quality soil, you’ll actually be restoring the proper order of things… and making all your future garden efforts easier!

Larry Hodgson is one of Canada’s best-known garden communicators. After studies at the University of Toronto and Laval University where he obtained his B.A. in modern languages in 1978, he succeeded in combining his language skills with his passion for gardening in a novel career as a garden writer and lecturer. 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 is a regular contributor to and horticultural consultant for Fleurs, Plantes, Jardins garden magazine and has written for many other garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening, Rebecca’s Garden 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 50 other titles in English and French. He can be seen in Quebec on French-language television and was notably a regular collaborator for 7 years on the TV shows Fleurs et Jardins and Salut Bonjour Weekend. He is the President of the Garden Writers Association Foundation and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. An avid proponent of garden tourism, he has lead garden tours throughout Canada and to the gardens of over 30 countries over the last 30 years. He presently resides in Quebec City, Quebec.

1 comment on “Gardening Myth: Adding Sand Will Lighten Clay Soil

  1. Pingback: How Can Soil Be Both Moist and Well-Drained? – Laidback Gardener

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