Underneath black tarps, sun-warmed weeds germinate, but are then extinguished by the absence of light. Large areas are often easier to cover with several 8-by-10-foot black tarps rather than one huge one. PHOTO BY BARBARA DAMROSCH

Behold a total eclipse of the lawn

The “O” word in gardening has long been “organic,” but this year it might be “occultation.” You might well ask what that means and what it has to do with the garden — or the occult.

The word occult, which can be used as a noun, an adjective or a verb, signifies something hidden, concealed from common forms of perception. Hence its relevance to paranormal phenomena, or closely guarded secrets. In astronomy, one celestial body can occult another, as when the moon hides the sun during a solar eclipse.

But let’s bring it a bit more down to earth — to the earth in your yard, that is. In this case, occultation means the spreading of something over the soil to exclude light, and thereby inhibit plants from growing. The word has come into recent use thanks to Canadian farmer Jean-Martin Fortier in his 2014 book “The Market Gardener.”

Fortier’s practice of preventing weeds by laying black tarps on the ground, inspired by European organic farmers, has in turn attracted the attention of other small-scale growers and, as often happens, the attention of home gardeners as well. He credits this technique with much of the success he’s had at his own farm, Les Jardins de la Grelinette, and another he supervises called La Ferme des Quatre-Temps, both in Quebec.

A tarp can smother weeds before planting and also deter future ones in a bed. Its dark color absorbs heat and warms the soil, Fortier explains; “Weeds germinate in the warm, moist conditions created by the tarp but are then killed by the absence of light.”

The tarp also improves the structure of the soil beneath. The heating of the soil does not harm its biological life; the bacteria, fungi and other microscopic soil-improvers are all fine.

Even after the mere two weeks necessary to germinate and terminate emergent weeds, the darkness-loving earthworms will have come up to the surface, tunneled the upper layer and, in effect, tilled it for you. It’s a joy to see them at work in moist, friable soil once the tarp is removed.

Let’s say you don’t have a garden yet, but there’s a part of the lawn you’re willing to sacrifice to have one, or to expand the one you have. You could till up the sod, or cut it in squares and shake the soil back into the ground. Better yet, turn the sod upside down so that little grass will regrow.

Best of all, you could lay down a tarp right now, and by July at the latest the grass will have decomposed and added excellent fertility to the new plot. Think of it as a total eclipse of the lawn.

Once the tarp is lifted there’s no need to till — just sow some spinach, carrots and brassicas such as kale and get ready for some good fall eating.

I’m not a gardener who loves to spread plastic in the garden, whether it’s plastic sheeting or woven landscape fabric. They do help keep down weeds, but they’re not a things of beauty. And at the end of their ungainly lives, they must be hauled away as trash.

There are biodegradable black films, but as yet none have been approved for use by organic growers by the USDA. Maybe future ones will be better.

So why do I give the black tarp my personal OK-for-now certification? Because it’s only on short-term loan to the garden. Dust it off and back it goes to covering the lawnmower, outdoor furniture and grill, patching a leaky roof, keeping the rain off the woodpile and stacked lumber, protecting the compost pile in winter, keeping trash from blowing out of the pickup en route to the dump, and draping over the arbor above the lunch table in case it rains.

Black tarps are readily available and come with bound edges, to prevent fraying, and grommets with which to tie them down. Carefully used, they’ll last a long time. For big areas, several 8-by-10-foot ones are easier to handle than one huge one, because you can more easily fold them up and store them when not in use. Ours are always in use.

Then again, ingenious growers often come up with other, highly original devices for garden occultation. An exchange I found in a forum on the site farmhack.org involved recycling old billboards to cover unplanted ground. One commenter wrote: “Was really tempted to leave Dolly Parton’s 12-foot head face up.” How could he not?

Barbara Damrosch

Barbara Damrosch

Barbara Damrosch’s latest book is “The Four Season Gardener’s Cookbook.”
Barbara Damrosch

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