Seasons Soil

A Spring Harvest of Rocks

In colder parts of the world, a curious phenomenon often takes place: stones and rocks—from pebbles to rocks larger than your head—seem to magically grow like mushrooms in fields and gardens. Every year, gardeners and farmers remove the ones that rose to the surface and the following year, new ones appear. In parts of the Northeastern United States, they’re so common they’re called New England potatoes and stone fences are built of them. Or huge piles of them can be found where a frustrated farmer moved the larger ones … often over hundreds of years (yes, they just keep on coming over centuries!). 

Farmers traditionally move the rocks out of their fields and use them to build stone fences. Photo: http://www.pinterest.com

These rocks re associated with glacial deposits: soils pushed to the spot thousands of years ago by glaciers mixing sand, clay … and stones of all shapes and sizes. The soil is full of them, often to great depths, and they keep migrating upwards over time … but why?

In cold climates, rocks and stones tend to migrate upwards due to the effects of freezing and thawing. Ill.: http://www.learner.org, montage: laidbackgardener.com

The science behind the phenomenon comes from the fact that rocks are better conductors of heat than soil. As a result, as winter sets in, the rocks take heat away from the warmer soil underneath. The soil beneath the rock, now colder, freezes before the soil above and, since it contains water and water expands as it freezes, the soil does too, pushing the rock upwards through the unfrozen soil above. In the spring, at snow melt, the space under the rock fills with soil, supporting it. And so it moves upwards, year after year, until it pops up in your garden.

Obviously, rock movement is going to be most evident in tilled soil, such as in a farmer’s field or a vegetable bed or annual flower garden left empty for the winter—places where there is nothing to prevent upward movement—and less so in forested areas, meadows or flower beds dominated by permanent plants like perennials, groundcovers and shrubs, where plant roots better hold the soil in place and help slow rock movement. Even so, rocks will continue to migrate upwards even in forests, just at a vastly slower rate.

In a way, being able to grow your own rocks is pretty cool! Maybe you could put them to good use and make a stone fence like your farmer ancestors used to do?

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.

4 comments on “A Spring Harvest of Rocks

  1. I smiled all through this post, because I pick them up every so often and have a small pile of them. It’s my own tiny stone wall. 🙂

  2. Margaret Schucker

    ‘The ground in New England grows stones.’ — folk saying

  3. I always noticed this and wondered why. Now I know! Thanks!

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