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does burning weeds kill the seeds

Flame weeding is considered an organic method of weed removal. However, if the weather is hot and the fire danger is moderate to extreme, Roundup may be the better option to avoid accidentally starting a fire or risking fines from the local fire district or other government agency.

An alternative to both Roundup and burning weeds is using cultural controls in the garden. Hand weeding and careful cultivation with a hoe around existing plants reduces the number of weeds in the landscape. However, digging deeply when removing existing weeds or adding compost and other amendments to the garden bed also exposes buried weed seeds, warns the University of California IPM Program.

Roundup in the Garden

If you’re using organic methods in the garden, flame torching is an approved method of weed destruction. The University of Minnesota Extension points out that flaming works best on young and broadleaf weeds, especially when applied at least twice per growing season.

Removing weeds before they can go to seed eliminates new seedlings. Mow the lawn at the recommended height to encourage thick turf that crowds out weeds. Alternately, you can accept a certain level of attractive natives and spring-flowering plants like violets (Viola spp.) and dandelions (Taraxacum spp.), hardy in USDA zones 3 through 9 and 10, respectively.

When using a flame weeder, you should put on closed-toe shoes, long pants, safety goggles and other safety gear as recommended by the manufacturer. Torching weeds is a matter of applying high heat but not actual fire. If flames are visible, you may be walking too slowly; dry plant matter or bark mulch is in the treatment area; or you’re holding the weeder too close to the weeds. Use caution when the weather is dry and/or windy to avoid starting a fire.

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When flame weeding, the most effective method is to catch weeds early, from 1-4 inches. At this small stage, flaming is nearly 100% effective at killing weeds, whereas weeds over 4 inches are more difficult to kill without multiple flamings.

Flame weeding is what we like to call a “slow kill”. Essentially, you are destroying cell structure in the plant leaf. The weed will no longer put energy toward growth (photosynthesis) taking the kill though the root system. YES, flame weeding will kill the roots too! Even on big weeds (over 6″), you will see a stunting effect and even a kill within a few days, depending on how established the root system is and how long the plant was exposed to heat. Again, multiple application may be necessary for well-established pants. When you see green – flame!

It is important to remember when flaming in and around desirable plants that heating those leaves can cause damage as well. Flame is not like a broadleaf herbicide in that it will only kill the weeds. Fire does not know the difference between desirable flowers and undesirable weeds. Thus, be careful around flowers and shrubs – particularly evergreens. Conifers are very flammable and should be avoided at all costs! Poison ivy, oak or any poisonous plant should be avoided also- the vapor/smoke from flamed leaves will cause a rash to your skin, eyes, and lungs! Yuck!

What’s the best advice we can give you? If in doubt, don’t. Always allow a safe distance between the flame and desirable plants, shrubs and trees. Always keep a fire extinguisher and water supply close in case of an emergency. Contact your local city or fire department to see if it safe to run a flame weeder in your area.

You do not want to burn weeds to ash! On smaller weeds, a slow walk is usually the best pace – just a split second of heat should kill unwanted weeds and grasses completely – you don’t need to burn them to a crisp. By nature, some grasses will return following a flaming. Repeat applications, however, will usually do the trick. For best results, increase exposure to the heat if weeds are wet from dew. Water on the leaves acts as insulation and decreases cell damage unless exposure time is increased. Note: it is ok to flame when it is wet out. In fact, we recommend it. Moisture will lessen the threat of ignition of dry debris.

A quick pass with the torch and you’ll see weeds wilt and die.

A thumb print on the weed leaf indicates success.

For a flame that starts safely and easily, look for one that has an ignition switch. These devices send a spark directly into the torch. You simply turn on the gas, hit the switch, and you’re on your way. Not all flamers are that easy to start, though. Many manufacturers provide flame-starting tools that you must hold near the gas outlet. These devices generate sparks that ignite the gas. They are simple and safe when used properly. Don’t use matches because your hands will be too close to the flame when it ignites.

Our early ancestors discovered fire and invented gardening. And even though farmers for centuries have used controlled burning to improve crops, it has not been until recently that home gardeners began to use mechanical flame torches, or flamers, in the garden. Of course, it’s never too late to invent a garden tool that kills unwanted weeds without requiring the gardener to bend and pull, disturb the soil, or lace both soil and crops with herbicides.

For effective weed control, use flamers in spring and early summer as annual and perennial weeds emerge. Killing larger, mature plants requires more heat, so save time and fuel by flaming weeds when they’re still young and tender.

Lanine and Orzolek both recommend using flamers as a pre-emergence control. Most viable annual weed seeds are in the top 1/4 inch of soil, and flamers can kill already-germinated seeds with heat.

Buying Tips: Features to Consider

For the home gardener, killing weeds is as easy as holding the flamer and walking slowly (1 to 2 miles an hour) between garden rows. Killing a weed requires heat for only 1/10 of a second.

Personal safety is another issue. These portable torches use pressurized tanks of propane and, if handled carelessly, can be hazardous. When operated properly, however, flamers are easy-to-use, safe, and timesaving gardening tools.