Flame weeding (also referred to as flaming) has been an apt option for organically ridding row crops and fields of uninvited weeds while also replenishing the soil with nutrients from the resulting carbon. Wedding the proficiency of flame with the compressed liquid power of propane has served many farmers and food producers well over the past century. According to the Northwest Coalition for Alternatives to Pesticide, the first agricultural flame weeder was patented in 1852.
Flame weeding is done by generating intense heat through a chosen device — whether it is a handheld torch or tractor-mounted — that sears the leaves of the weeds, which causes the cell sap to expand, thusly damaging the cell walls. “You’re watching for the color change, depending on the weed and its maturity,” said Charles House of Earth & Sky Solutions. Leaves wilt and dehydrate the plant, leaving the invaders no other option than to die, sometimes up to three days later.
“The key to successful flame weeding is the maturity of the plant you’re trying to eradicate. The smaller, the better,” he explains. The best time is when they’re immature and in the cotyledon stage.
Flame Weeding Background
Flaming gained popularity in the first third of the 20th century and continued through the 1960s until pesticides replaced industry attentions. Though its use waned over the following 20 years, flame weeding resurfaced and regained popularity in the early 1990s, and continues to be used today. So continues flame weeding’s renaissance.
One man whose agricultural history includes using and refining his flame weeding technique is Charles House. Approximately 30 years of experience in many sectors of green industry has endowed him with ample knowledge. As a purveyor of agricultural farm equipment and owner of Earth & Sky Solutions, based in White Hall, Virginia, he has been able to create a business model in which he can share the knowledge he gained from his years of experience.
“When I owned a landscape company, I got into using chemicals for a time because that’s what the market wanted. I got tired of it. And in fact, I refuse to use chemicals anymore.” His experiences have allowed him to contour his personal and professional philosophy and act as an educational and consultation resource for people who may not know much about flame weeding and its benefits, but are interested in learning. For House, flame weeding is possibly the most logical answer to eradicating weeds.
“With flame weeding you don’t have to use chemicals. There are so many benefits, [among which are that] you don’t have to worry about drip.”
Fueled by propane, flame weeding allows the user to not worry about spillage or drip, since it’s safely contained and is accessible on an as-needed basis. Says House, “When propane is under moderate pressure, about 200 psi, it remains liquid and burns anywhere from 1200 to 2000°F, averaging at about 1400°F.” This range is thoroughly sufficient to eliminate weeds in a garden or in row crops organically, quickly and easily.
Of course many, if not all of us, know better than to play with liquid propane, right? Another issue that may seem obvious would be to use it with a lot of ventilation — and since you’ll be flame weeding your yard or row crops outside, that shouldn’t be a problem. It’s always important to prevent electrostatic charges from building up when in a liquid state, outside of the cylinder. And, if you have an open container of liquid propane, don’t use any hand tools, or anything that sparks, within the vicinity. Always wear protective clothing. Some people even use face shields. If there’s a spill, propane will evaporate quickly.
“Many organic farmers opt for flame weeding, since there are no side effects or environmental ramifications.” Another positive aspect of flame weeding is that, as House explains, “You’re not cultivating the soil. When you cultivate soil, you’re digging up weed seeds that will [eventually] germinate — it’s like a no-till type method. You’re using the flame to disrupt the growth of the weeds.”
Flame Weeding Methods
There are three methods of flame weeding: spot-flaming, pre-emergent flaming and indiscriminately treating whole beds. The stale seedbed technique begins controlling weeds early in the season, especially in direct-seeded crops, according to Appropriate Technology Transfer for Rural Areas (ATTRA). When the seedbed is prepared, the soil is tilled and set/hilled into beds, which encourages weeds to germinate and make their way to the surface. In order to have a weed-free bed, farmers will flame the soil after tillage, but prior to planting to ensure the seed crops have precedence. Some farmers will even pre-irrigate to induce weed growth, and then sweep through with the flame to kill them all off. This technique can also be helpful when preparing to transplant, essentially giving the vegetable seeds a head start so that they can develop the canopy cover that will greatly reduce weeds’ ability to flourish. The earlier the weeds are taken care of, the better it is for the crops to maximize their yield.
The pre-emergence flaming technique eliminates the first round of weed seedlings just before the crop seedlings emerge, since the weeds often surface first. This ensures the crop will not be harmed and nicely compliments crops that are slow to germinate.
House discussed post-emergence flaming, also known as “selective flaming,” a fair amount throughout our interview. This technique requires more finesse and control, since the crop plants have broken through the surface and are stretching their way toward the sunlight. Although it may seem counter-intuitive to brush your crops with over 1200°F of propane-fueled fire, time is of the essence, and hardy plants can stand it. Once the row crop is out of the cotyledon stage, it will be much more likely to withstand the heat.
There are myriad flaming techniques outside of these three. Some farmers opt to cross flame, parallel flame, middle flame, and there’s even water-shielded flaming. “Torque adjustment is key, as well as the maturity of the plant that you’re trying to protect, and ground speed,” House says.
Subtle movements and being mindful of velocity and tension can make for fast, efficient work. “Penetration of the flame is only a few centimeters into the soil, and when you flame, you leave organic matter in the soil,” House explains. This is essentially biochar.
According to the CarbonZero Project, biochar is “created using a pyrolysis process,” which is the thermochemical decomposition of an organic element. In the case of flame weeding, the organic elements are the uninvited weeds that are trying to be eradicated. To further elaborate on a seemingly simple process, a “biomass is heated in a low oxygen environment, and once the pyrolysis reaction has begun, it is self-sustaining, and requires no outside energy input.” When a farmer flame weeds his or her row crop, this process is occurring with each sweep of the flame-tipped hose.
In many cases, when farmers use biochar on crops, it’s spread across the top layer of soil. Flame weeding omits the physical application of biochar, saving farmers time while adding nutrients to the soil that turns something invasive and uninvited, into a helpful, nourishing presence. A generous amount of research shows that it can increase crop yields. Biochar has high porosity and has been known to retain moisture and replenish organic carbon levels in the soil; further, it also prevents fertilizer runoff and leeching, which decreases the need for fertilizers, and ultimately decreases pollution of soil and surrounding areas.
Deciding on whether or not to flame weeds depends on the condition of the site, and exercising good, old-fashioned common sense is the best policy. It never hurts to dig into the soil to test the seedlings’ progress. Physically knowing where the plant is will always help you best gauge when and when not to flame. Asking oneself if the crop has grown too large so that the method of flaming has become prohibitive is a viable starting point. Essentially, can you get in there? If not, you may want to change the device, but if that’s cost-prohibitive, other options should be explored.
As with most things, flame weeding proficiency comes with repetition. The more you do it, the more you can refine your technique. A popular method is to use a sweeping motion, “away from your body, but it all depends on what type of unit you’re using,” House cautions. “With a hand torch, it’s typically a sweeping motion. Think about using an eraser — flame weeding is really a weed eraser.”
He suggests to “do some prep first and get combustible materials out of the way before flaming. Combustible material has a life span of its own.” That life span can be, and often is, short, but it can also be more protracted, so be careful. “Stay away from rayon,” he says facetiously, though with seriousness.
“Some people say they get better results when they flame when it’s still a bit wet,” House explains, since “water is a really good conductor of heat.”
On the whole, flame weeding may be one of the best options for ridding one’s space, whether a garden or a multiple-acre farm of weeds. As an organic process, its benefits are twofold: as it kills weeds and gives crops or other plants an opportunity to grow, it replenishes the soil of nutrients without any human effort. As a succession of natural processes, it’s both accessible and intuitive, making it a universal tool for farmers across scales.
By Francesca Camillo. This article was originally published in the May 2012 issue of Acres U.S.A.