Flame Weeding

Flame weeding uses the heat generated from one or more propane burners to kill weeds.4 Flame weeders can be either handheld or tractor-mounted. Home use models range in size with some small enough to carry (see the Mini Dragon above) or attached to a propane tank wheeled on a cart or in a backpack. They all work in the same way. Intense heat sears the leaves of the weeds, causing the cell sap to expand, damaging cell walls. This causes leaves to wilt and prevents water from moving from the roots to the leaves. In a short period of time, the plant withers and dies.5 The plant is not actually burned. 

How to Flame Weed in One Easy Lesson

Flame weeding, like other forms of weeding, must be timed right. It is best to catch the weeds at a young stage when the cotyledons, the first true leaves of the plant, are first beginning to show, usually when the plant is one to two inches tall. Depending on the weed, even plants up to four inches tall can be effectively flame weeded, if done right.6 Broadleaf plants are much more susceptible to flaming than grasses, because of the thinner, larger leaves. To be effective, pass the flaming wand slowly about three to six inches above the target weeds.2 An observable “sag” in the weed indicates that it has been heated long enough. 

Plants do not die instantly. In fact, there may be little noticeable difference after treatment for a couple of hours, even up to a day. Remember, it is not necessary to burn the plants to the point of ashes, you only need to flame the plant for a split second;6 a sag indicates that the weed has been killed. For larger weeds, grasses and plants that are wet, more than one flame treatment may be needed to fully kill the plants.6

Caution

Please be very careful when flame weeding! Make sure to check for fire bans in dry areas, and keep a fire extinguisher and water supply nearby just in case. Always wear protective clothing: gloves, pants and closed-toe shoes.

There are certain plants that you need to look out for when flame weeding, to prevent fire and keep yourself safe. Conifers are very flammable and should be avoided.6 Poison ivy, poison oak, and any other poisonous plants should never be flamed as that can create hazardous vapors and result in rashes on your skin, eyes and lungs.6

Three Methods

There are three basic ways to use flame weeders in gardens and on farms: 

  1. Selective Spot Flaming: With spot flaming, specific weeds are targeted and flamed directly. This method is generally used when the desirable plants or crop are big enough to be readily distinguished from the weeds. Be careful not to flame your desired plants!6
  2. Non-Selective Flaming: is used when both the weeds and desired plants are at a similar height. With certain hardier plants such as corn, onion, and garlic, the tops in their early stages of development can be flamed without doing any lasting damage.7 The plants may temporarily die back, but should recover without reducing yields while the adjacent, less hardy weeds are destroyed.
  3. Flame Before Planting: Before seeds are planted, or after seeds have been planted and before they have emerged from the ground, flame weeding can be used to destroy the first emerging round of weeds when they are very young. This helps cut down on the weed pressure the newly emerging crop seeds will experience. Flaming can also be used to reduce weed pressure in garden beds that are being readied for transplants.4

Where to Find Them

Flame weeders can often be found at your local garden or farm supply store, and they are also available online. A handful of companies manufacture and sell flame weeding products, including Flame Engineering and Flame King. Expect to pay less than $100 for a smaller model suitable for home use. If the price seems high, you could chip in and buy one with several friends and neighbors or see if your local tool-lending library has one available!


More About Flame Weeding

Since the beginning of civilization, fire has been a tool for managing vegetative growth in the landscape. One source lists eleven major uses of fire by Native Americans: for hunting, crop management, improving growth and yields, fireproofing, insect collection for consumption, pest management, warfare, “economic extortion,” clearing areas for travel, felling trees and clearing riparian areas.1

Flame Weeding in Agriculture

Flame weeding as we know it has been around since the mid-1800s. The first agricultural flame weeder, or flamer, was patented in 1852.2 However, it wasn’t until the 1940s that flame weeding became recognized as an effective tool in crops such as cotton, sugar cane and corn.2 By 1965, there were roughly 25,000 flame weeders in commercial use, but as herbicides became popular, flame weeding nearly died out. By 1990, flame weeding was in use on approximately 10,000 acres around the U.S.3 In recent years with renewed interest in pesticide-free weed control, gardeners and farmers have been using flame weeding more and more.

Non-Agricultural Uses

Flame weeders have also found favor among homeowners as a maintenance tool around the yard and driveway. Flame weeders are great tools to use around fence lines, brick and other garden paths, and on gravel driveways or in driveway cracks. However, don’t use them around the lawn. They will leave brown burnt spots that aren’t very attractive! Parks departments are using them to maintain cracks in sidewalks and parking lots, around sign posts, and to weed baseball fields.

Advantages

One other big plus for flame weeding is that it is easier on your body, cutting down on the amount of time you need to spend bent over hoeing or hand weeding. However, the backpack flame weeder is quite heavy, so be careful when using it. Whatever method you use, staying ahead of the weeds is key to keeping your garden and property at its best. Flame weeders are very efficient tools when used correctly. Used along with a hoe, there should be no need to ever use herbicides in the small farm, garden or around the yard.

NCAP Experiences

NCAP staff have used flame weeders in a variety of volunteer weed management events, including one in 2020 at Arbor Lodge Park in Portland. Arbor Lodge is Portland's largest pesticide-free park and utilizes volunteers throughout the year to keep the park looking beautiful while also being healthy for people and pets. Flame weeders were used along concrete cracks near the baseball field to kill weeds. In our experience, flame weeders work best when there isn't much wind as the flame can go out easily. If you can mow or weed wack tall weeds directly before using the flame weeder, you'll have better success. 

Article originally written by Brad Cohen, 2006; Updated 2021


References
  1. Grubinger V. 2004 May. Flaming stale seedbeds for weed control [Internet]. Univ. of Vermont Extension. Available from www.uvm.edu/vtvegandberry/factsheets/flameweeding.html
  2. Rifai MN. 1997. Flame-weeding in organic vegetable farms. Nova Scotia Agricultural College. Available from https://grants.ofrf.org/system/files/outcomes/rifai_94-30.pdf
  3. Flame weeding 101 [Internet]. La Crosse (KS): Flame Engineering Inc; undated [cited 2021 Sept 16]. Available from flameengineering.com/pages/flame-weeding-101
  4. Daar S. 1987. Update: Flame-weeding on European farms. IPM Practitioner. 11(3):1-4.
  5. Diver S. 2002. Flame weeding for vegetable crops [Internet]. Available from https://attra.ncat.org/product/flame-weeding-for-vegetable-crops/
  6. Williams GW. 2003. References on the American Indian use of fire in ecosystems. USDA Forest Service, Washington, DC. Available from https://www.itcnet.org/file_download/5d76d377-8025-4780-8511-4dc8d0596e45
  7. Heiniger RW. 1998. Controlling weeds in organic crops through the use of flame weeders. Organic Farming Research Foundation. Available from https://grants.ofrf.org/system/files/outcomes/heiniger_94-43.pdf

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