Sonja Birthisel, postdoctoral research associate at the University of Maine, flaming weeds. Credit: Courtesy of Johnny Sanchez

This story was originally published in June 2020.

Don’t let anyone convince you the gardening is all grandmas and fresh produce: sometimes there are flamethrowers involved.

Flame weeding, often called “flaming,” is one method for natural weed management by passing a flame over a weed briefly to heat the plant tissues just enough to kill them. The plants will start to look dull and wilt a bit. The method can be effective — and, let’s be honest, awesome — but it also isn’t appropriate for every situation.

“It works really well in certain situations,” said Kate Garland, horticultural specialist at the University of Maine Cooperative Extension. “It can work really well on young [weed] seedlings, [on] gravel driveways or walkways free of organic debris that’s flammable.”

Flaming is a less effective weed control method for perennial weeds, which have extensive below-ground root systems from which new weeds can emerge even after the above-ground portions have perished.

“It kills the cell on the above ground portion of your weeds,” said Sonja Birthisel, postdoctoral research associate at the University of Maine. “Some species are more resistant to death by heat than others. If you have perennial weeds you might need a little bit higher propane dose or go back over it multiple times.”

The technique can work in backyard vegetable gardens if you want to kill a flush of early weeds prior to planting, Birthisel said.

“You can do this by tilling the soil and waiting for a first flush of weeds to come up and using a propane torch and flaming a couple of weeks before planting,” she explained.

Advantages and disadvantages to flame weeding

The advantage to using the flame weeding method over other natural weeding methods is its efficiency.

“It can be pretty quick,” Garland said. “If you have a cropping system where you have pretty small seedlings and you can catch them early and do it frequently, it is a fast way of weeding.”

One of the downsides to flame weeding in gardens is that it’s hard to expose the weeds to the flame without exposing your crops as well, but it is possible to work around this through timing and careful application of flaming.

“I would recommend doing it before you plant, or using it very carefully between plants or in the rows between your beds if you want to control later season weeds that way,” Birthisel said. “Just know that there’s a danger of getting that flamer too close.”

Plus, it is not especially environmentally-friendly because it utilizes fossil fuels.

“If you are fossil fuel conscious, it could be that mulching is more appropriate,” Birthisel said.

When not to flame

There are certain scenarios where flaming is not appropriate.

“It would be totally inappropriate to use this method near things that are potentially flammable. If you’ve got a brush pile that would be out of control if it went up in flames,” Birthisel said. “I’d be hesitant about using this practice if I lived in Southern California or a place that’s prone to wildfires. I would recommend people check with their local ordinances before applying this practice.”

Birthisel also strongly cautioned against burning poisonous or noxious weeds like poison ivy. The results can be painful, both for the person weeding and those breathing the air around them.

“When you burn poison ivy, it can get those noxious compounds up in the air,” she explained. “People can inhale them and have really nasty issues with getting poison ivy in [their] lungs.”

Choosing a torch

A flame weeder generally consists of a wand connected to a propane tank by a hose accompanied by some sort of dolley or carrying apparatus.

“I have a backpack model that’s basically a pretty similar propane tank mounted on a backpack,” Birthisel said. “I walk and use [it] to torch weeds. That’s pretty popular and I see backyard gardeners and farmers using that.”

Another popular model is basically a propane tank on wheels with a torch attached, Birthisel said. She recommended shopping around for different models to see what is most comfortable and accessible to you.

“And, of course, read up and make sure you’re following the directions on any flame weeder that you buy,” she added. “I have seen issues where people accidentally set a bush on fire, so handle with care [and] have the hose nearby.”