Using fire to kill weeds

As an exercise, let’s apply the four elements of the classical world — earth, air, fire and water — to the garden. Earth comes first, because you certainly can’t grow much without soil. You’ll also need air in that soil or plant roots will decay and soil organisms will perish. And not much survives, or thrives, without water.

The need for fire is a little less obvious. Though dangerous, it can be a major regenerative force in forests and grasslands. And it can also be a major ally in the war on weeds.

(istockphoto)

Using a blast of fiery heat to kill weeds is an old technique and one applied quite commonly in agriculture, as befits the size of your plot. It’s a great way to kill a lot of weeds quickly without resorting to herbicides. The trick is not to set the intruding plant on fire, but merely to break down its cell structure so that it dies. It might not look dead right away, but wait a few hours and — pfffft. Large farms use tractor-pulled flamers that roar across a field. Our small farm uses hand-held flaming wands, each fueled by a three-gallon propane tank mounted on a backpack. (Tanks can also be pulled along on a dolly.)

For the home garden, we have an even simpler, lightweight wand, shaped like a cane, to which you attach a one-quart propane canister. With this you can blast a stubborn dandelion, perhaps not into oblivion, but into a submission more long-lasting than with a dose of boiling water or vinegar, two approaches that are “better than nothing” but no more.

Our favorite flaming technique, however, is the preemergent treatment of weeds. Nobody likes to weed a large bed of young carrot plants, which are far too dainty to shade weeds out. Allowing the bed to sprout its surface weeds for two weeks, then flaming them, can buy the crop time before weeds pose a threat.

Here’s the ingenious part: Flaming after you sow the carrots gives more weeds a bit of time to emerge. So we burn them after the carrot seeds have been in the ground a few days and are on the verge of germinating. How do we know that is about to happen? By placing a pane of glass over a small area of the bed. When we see seedlings beneath the glass pushing through the earth, we know the rest of the bed will sprout the next day. Use a box frame to keep the pane an inch off the ground.

If you flame immediately, you kill all the latest crop of small weeds while the carrot seeds are still safely underground. For summer carrot sowings, when the sun is hotter, we don’t use the glass but simply flame five days after sowing the crop.

There are a number of simple, lightweight flame weeders on the market, some available at mass merchandisers and hardware stores. Some types employ an actual flame; others use infrared heat. The flame is hotter, but both methods work and are not at all scary. The Bernzomatic Self-Igniting 20,000 BTU Outdoor Torch, for example, available from Amazon.com for $33, would easily handle the average-size garden. And a large creme brulee.

Damrosch is a freelance writer and the author of “The Garden Primer.”

 
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