People who declare them useless perhaps don't know how best to use them. My own belief stems from success which isn't really arguable. Anyone wishing to visit and see the results of correct use are welcome to do so. Of course glyphosphate works. It's just a personal choice whether to use it or not. If not, then a good weed wand, correctly used, does the trick.

Flame Weeding in the Garden
By Sheila Daar - Flame Engineering

Using heat to manipulate vegetation is an ancient horticultural technique. Native Americans used fire to keep brush out of grass lands for centuries, and farmers in the southern U.S. have pulled tractor-powered flamers across orchard rows and through fields of cotton, sugarcane, and corn since 1852, when the first flaming equipment was patented. Use of flamers in agriculture declined in the 1950's when the romance with herbicides was going strong. It experienced a revival in the mid-1960's when some of the short-comings of chemicals, including shifts of weed species, herbicide damage to crops and cost, made flaming attractive again.

Today flaming is used to control weeds in row crops, orchards and along fencelines and water-ways. A flamer has even been use to control stray weeds in the pavement in front of the Kennedy Centre in Washington, D.C. Given the long history of flame weeding in the U.S. it is ironic that this method has never caught on with American gardeners, while in Europe it is a common weed control technique for residential gardens and urban parks.

How Flaming Works
Before you conjure up an image of massive grass fires and "controlled burns", let me assure you I am not referring to these methods. Flaming utilises a propane or kerosene-fired torch, mounted on a long wand, to sear the tops of young weeds. The flame produces temperatures of 2,000oF (1,093°C), heating the sap in the cell walls of the plant tissue and causing the walls to expand and rupture. The weed wilts and dies, although it may take up to 24 hours before death is apparent.

How to Use a Flamer
There is an art and a science to flaming weeds. The mistake people often make is to assume that they must hold the flame on the weed until they see the plant burn up or at least look sizzled and scorched. Nothing could be farther from the truth. If the flamer is held over weeds long enough to blacken them, the ultimate effect may be to stimulate growth from the remaining roots. The whole point of flaming is to heat the cell sap, which is accomplished by slowly passing the flame over the plant. (A wonderful anecdote about how this "searing" technique was discovered is shown in the sidebar.) You may not see an evidence of wilting, let alone plant death, for several hours or even until the next day.

When first using a flamer, a little experimentation will be necessary to see what works best with your weed situation. In general, a good technique is to hold the torch three to six inches above the weeds, and walk slowly along the weedy area while lightly searing the weeds. If you are treating a large expanse of weedy ground such as a newly-prepared seedbed, point the torch at the weeds, and wave the wand in a scythe-like motion. Some manufacturers of flamers recommend a two-step approach. The first is to sear the weeds as described above. Once the weeds are dead and dried out (i.e. a day or two later), they recommend returning with the flamer to incinerate the dead vegetation on the spot, eliminating the need to gather and remove the dead weeds.

Leaves that have been heated sufficiently to burst cell walls will feel very soft to the touch and may turn a purplish colour before wilting and dying. Thus, when you are first trying this technique, use this touch test on the weeds. With some experience you will learn how long to hold the flame to the plant. Remember that the hottest part of the flame is an invisible cone sur-rounding the visible portion you should hold the flamer nozzle an inch or more above the weeds for optimum heating.

Once the weeds have wilted and died, you can remove them to the compost pile, or pass the flamer over the dead material and burn it into ash, which can be left on the soil as a source of minerals.



The technique of "searing" rather than burning plants with flamers was stumbled upon by accident in the 1930s. As reported by Corkins and Elledge in the May, 1940, issue of Reclamation Era, it happened like this:

John Hendreschke, county pest inspector in the Eden Valley, Wyoming, was burning a patch of bindweed (morning-glory) (Convolvulus arvensis) which had developed mature seeds. The growth was heavy and thick and John was doing a good job of burning it up. In fact, he was doing such a good job that by the time it was half done, his burning fuel had been three-fourths used up. So it was a matter either of making a long trip after more fuel or taking a chance on getting the job done with a rapid, light burning. He chose the latter and proceeded to quickly sear the tops of the plants on the rest of the patch.

John got his surprise when he went back to treat this patch the next summer. The part which he had given a "good job" of heavy burning seemed to have been stimulated by the treatment and the growth was heavier and ranker than before. The part that he had given the "poor job" of light searing of the top foliage was thinned by at least half and the remaining plants were sickly and weak.



Flaming Works Best on Young Weeds
Flame weeding is most effective on young annual and perennial weeds no taller than one to two inches (three- to five-leaf stage), because at that point the fragile root system is killed along with the top growth. When flamed at this stage, weeds such as shepherds-purse, Capsella bursa-pastoris; chamomile, Matricaria chamoillia; and annual bluegrass, Poa annua; quickly succumb. For unknown reasons, some annual weeds like lambsquaters, Chenosodium album, and common groundsel, Senecio vulgaris, also readily die at later stages of growth with a single pass of the flamer.

Mature stands of perennial weeds such as johnsongrass, Sorghum halepense, Canada thistle, Cirsium arvense, and even wild morningglory, Convolvulus arvensis, also succumb to flaming, but only after a number of treatments. One pass of the flamer may kill the tops of perennial weeds, but new growth will regenerate from the below-ground roots. However, repeated flaming - several times in a season, or spread over a season or two - eventually starves the roots and kills the weed.

Timing on Grasses is Critical
Broadleaf weeds are far more susceptible to control by flaming than are grasses. The fact that grasses evolved in environments where fire was a natural component of the ecosystem may explain their relative heat resistance. When grasses are about one inch tall (2 to 3 cm), they develop a protective sheath that can shield the growing point from the heat, allowing regrowth of tillers. Thus, if the flaming treatment is delayed until the sheath has formed, grasses will suffer a setback,but will not die. Thus, if you want to kill grasses, flame them before they exceed an inch in height. However, if you want to kill broadleaf weeds in a lawn, any grass that you accidentally sear that is more than one inch tall will quickly recover. Thus, flaming is a practical option for lawn weed control.

Flamers Useful in Many Sites
In European gardens, flamers are used for pre-emergent weed control in seedbeds, to weed between rows in vegetable and ornamental plantings, to clear weeds from flagstone and brick paths, from fencelines, drains and ditches, and to incinerate garden clippings. For example, prior to planting seeds or transplants into garden beds, European gardeners cultivated and level the beds, then irrigate them to encourage weed seeds to geminate. As soon as a green "fuzz" appears on the soil surface, they pass the flamer over the soil to kill the germinated weeds as well as any weed seeds lying on or near the soil surface. Seeds or transplants are planted following the flaming. Followup flaming can be done between rows if needed, although with the start they have on the weeds, most vegetables or flowers can shade out any weeds that pop up post-flaming.

Some Precautions
Flaming on dry, sunny days is recommended. Weeds growing in dry areas tend to respond more quickly to flaming than those growing in moist habitats, perhaps because available moisture gives plants more resistance to the heat. Do not flame near fuel storage tanks or lines, as there may be small fuel leaks that could ignite. When dealing with large areas of weed growth, work in sections, so that areas where weeds have not been flame-killed provide effective fire breaks - just in case some unseen dried material becomes ignited. Green plants undergoing flame-treatment rarely ever ignite.

Flamers Kill Insects and Pathogens
While this article has focused on the weed control benefits of flaming, this technique also has other pest control applications. For example, potato plants up to eight inches (20.3 cm) tall can be flamed to kill Colorado potato beetles, Leptinotarsa decemlineata, without causing undue damage to the potato plants. Flamers can also be used to incinerate fallen fruit and mulch that harbors over-wintering spores that cause powdery mildew, brown rot, and other plant diseases. Given their versatility, flamers appear to be very useful garden tools - particularly for those seeking alternatives to toxic materials. Hopefully, a wider array of garden-sized flaming equipment will become available, and these tools will become more widely appreciated by North American gardeners.