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Modified torches allow garderners to easily spot treat weeds.

Flame weeders, also known as weed torches, garden torches and by various brand names, are a viable option for weed control in the right setting. Very simply described, they are a modified torch that allows gardeners to easily spot treat weeds growing in sidewalks, driveways, patios and other inflammable surfaces. Heat produced by the torch damages above-ground plant tissue, causing the affected plant to die back to the soil surface.

Flame weeders have been around for decades, but only recently have become more widely available to consumers with some hardware and tool stores starting to carry them. They are still widely available online and through garden supply businesses. Small and simple flame weeders start around $25, and prices go up with longer hoses, carts and other special features.

There are two types of flame weeders — ones that attach to small propane bottles (the type used with a small torch or for camping) and ones that attach to large propane bottles (the type used with a grill).

The type of flame weeder that attaches to a small propane bottle is usually shaped like a J, with the curve being the handle. The propane bottle attaches to the short end and the flame comes out the end of the long straight side. These small weeders work best for small, tender weeds and spaces where the user wants a lot of control over the flame.

Flame weeders that attach to large propane bottles usually have an arm where the flame will come out and a hose that attaches to the bottle. There is a lot of variability in the length of the arm and the length of the hose and both make a difference in comfort and convenience for the user. When selecting one of these weeders, check the fit by standing with the handle in hand and see how far the flame end is from the ground. If stopping or leaning is needed to get the flame with a few inches of the ground, look for a weeder with a longer arm.

Hose length is all about convenience. The length dictates how far from the heavy bottle the user can travel. With a short hose, the bottle needs to be carried by the torch user, transported on a cart that is easily moved in the work area, or picked up and moved constantly. A long hose allows the user to set the bottle down while they cover an area, or at least spend less time moving the bottle.

One accessory to look for on both types of flame weeders is an ignitor. This is a push-button sparker that works similarly to the lighter on a grill. Without it, the torch must be lit with a handheld sparker or other lighting device which can be a bit more intimidating.

When using a flame weeder, use extreme caution to avoid starting a fire or burning something unintentionally. Keep the flame to surfaces that won’t catch fire, such as concrete, stone, brick, asphalt, bare soil, etc. Also, heat radiates out a few inches from the visible flame. Keep it away from desirable plants and objects that could be damaged by the heat.

To kill weeds with a flame weeder, pass the flame over the weed or hold it over long enough for plant tissues to be damaged. Target the flame at the crown or base of the plant. Exactly how long a plant should be flamed depends on the plant species, maturity, moisture levels and other factors, but in most cases a few seconds is enough. Look for a dulling of the leaves and/or wilting of the plant.

If weeds are still green after a few days, flame them again for just a bit longer. Burning the whole top of the plant is unnecessary and time consuming.

Weeds are easiest to kill when they are small and tender. If weeds are very large, try mowing or weedeating them first and torching what is left.

Perennial weeds are likely to regrow from the roots after a few weeks or a month. Continue treating them through the season. With repeated torching, root systems become depleted and even the toughest weeds will die over time. Some annual weeds, especially those with thick stems or leaves, will also regrow. Re-treat at least often enough to prevent them from producing seed to reduce the number of weeds that grow next year.

Flame weeding was a common practice in conventional agriculture in the U.S. in the 1940s and 1950s. Farmers used diesel fuel instead of propane at the time. In the last few decades, flame weeding has regained popularity as a means of reducing herbicide use.

— Jennifer Smith is a former horticulture extension agent for K-State Research and Extension and horticulturist for Lawrence Parks and Recreation.