Kill Weeds With Heat

Annual weeds, such as lambsquarters, are quickly killed by heat

Our early ancestors discovered fire and invented gardening. And even though farmers for centuries have used controlled burning to improve crops, it has not been until recently that home gardeners began to use mechanical flame torches, or flamers, in the garden. Of course, it's never too late to invent a garden tool that kills unwanted weeds without requiring the gardener to bend and pull, disturb the soil, or lace both soil and crops with herbicides.

Though flaming technology has been around since the 1940s, home gardeners have expressed renewed interest in these weed-fighting tools. Flamers require no chemicals, and don't result in groundwater contamination or chemical residues on garden crops. But safety concerns of another type remain. Never use flame torches around any dry, brown, or otherwise flammable material. Also, their use during dry periods in forested or arid regions is prohibited, or ought to be. Always check with your local fire department or town clerk before investing in a flamer.

Personal safety is another issue. These portable torches use pressurized tanks of propane and, if handled carelessly, can be hazardous. When operated properly, however, flamers are easy-to-use, safe, and timesaving gardening tools.

Using Flamers

Flamers are portable gas torches that produce intense heat (about 2,000°F). When you pass the flame over and around weeds, it quickly boils the water in the plants' cells, causing them to burst. Once the heat destroys any section of a weed's stem, for instance, water and nutrients cannot reach the leaves, and the top part of the weed dies.

For the home gardener, killing weeds is as easy as holding the flamer and walking slowly (1 to 2 miles an hour) between garden rows. Killing a weed requires heat for only 1/10 of a second.

"You know you're successful when the weed changes from a glossy to a matte finish," says Tom Lanine, weed ecologist at the University of California at Davis. "The weed may not droop immediately but will wilt and die within a few hours. Then you just leave the weed to compost naturally. You don't want to disturb the soil and bring more weed seeds to the top."

For effective weed control, use flamers in spring and early summer as annual and perennial weeds emerge. Killing larger, mature plants requires more heat, so save time and fuel by flaming weeds when they're still young and tender.

For effective control, Penn State vegetable specialist Mike Orzolek recommends a series of flaming attempts, 2 to 3 weeks apart. Flaming kills annual weeds completely (though more annual weeds will pop up), but it doesn't kill the roots of perennial weeds. These will send up new shoots within a week or so after flaming. Additional treatments will eventually deplete the roots' stored energy, and the weeds will die.

Lanine and Orzolek both recommend using flamers as a pre-emergence control. Most viable annual weed seeds are in the top 1/4 inch of soil, and flamers can kill already-germinated seeds with heat.

Lanine recommends watering the soil before applying heat. "Unless the seeds have sprouted, there's no way to kill them with flamers. Even when they've sprouted, the soil is an incredible insulator," he says. "However, if the soil is saturated with water, then you will get some conduction of heat and can kill some seedlings in the soil."

Buying Tips: Features to Consider

Flamers are long metal tubes that carry gas to the flaming tip. The function sounds simple enough, but some products have features that make weeding both easier and safer.

Cost

Flamers are available in garden centers and in many gardening and homeowner catalogs. Expect to pay $50 to $90 for a flamer, which should include an extension hose and gas regulator. The gas tank and propane are sold separately. A 5-gallon (20-pound) tank costs about $20 to $25 in hardware stores, and fuel will be about a dollar a gallon.

Easy Starting

For a flame that starts safely and easily, look for one that has an ignition switch. These devices send a spark directly into the torch. You simply turn on the gas, hit the switch, and you're on your way. Not all flamers are that easy to start, though. Many manufacturers provide flame-starting tools that you must hold near the gas outlet. These devices generate sparks that ignite the gas. They are simple and safe when used properly. Don't use matches because your hands will be too close to the flame when it ignites.

Tank Size

Some flamers attach directly to small propane tanks (14 to 16 ounces). This makes them easier to maneuver, but they burn for only 1 to 1 1/2 hours. Flamers attached to large tanks (like those used with barbecue grills) need an extension hose, that runs from the tank to the flamer. The hose length limits your range, however, and you must lug the tank around. Use a dolly if the tank is too heavy to move around comfortably, but make sure you strap the tank down securely.

Burning Time

Most flamers include valves that allow you to adjust the flame from low to high settings. How much fuel you use will depend on the size of the burning tip and your flame-adjustment setting. Typically, a 5-gallon gas tank will provide enough for 3 to 6 hours of burning. However, a flamer with a 3-inch tip at full throttle will burn 20 pounds of fuel (about 5 gallons) in an hour.

The Size of the Burning Tip

Tip size is important, and you should consider the type of weeding you want to do. For example, if you'll be working in tight spaces, you'll have much better control using a torch with a tip (burning end) that produces a fine flame. Remember, a 2,000°F flame will kill prized garden plants just as easily as it will kill unwanted weeds. If you need to manage heavy weed growth over a large area, buy a flamer with a 1 1/2- to 3-inch-diameter tip. Flamers with these tips, sometimes called torch bells, send out a wider flame band than other models, allowing you to cover more area in less time. For most home gardeners, flamers with 3/4- to 1 1/2-inch tips are best.

Safety

When used properly, flamers provide effective weed control.

Here are a few important safety tips:

  • Never flame weeds during extremely dry periods. Flamers produce intense heat; even wet mulch will ignite. Don't flame if you have any debris around and as little as a 3- to 5-mile-per-hour wind.
  • If you're using a flamer with an extension hose, keep the flame away from both hose and tank.
  • Though the flamer's handle doesn't get hot, the flaming tip does. Even after turning off the flame, keep the flamer away from people and combustible materials.
  • Always be cautious when lighting the flamer. Follow the manufacturer's instructions exactly.

Dan Hickey is a former editor of National Gardening.

This article is categorized under:
Articles → General → Landscaping → Lawns, Ground Cover, and Wildflowers
Articles → General → Garden Care → Pests and Problems
Articles → General → Garden Care → Tools and Equipment
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