The flame weeder is run over the beds of slow-germinating crops such as beets, carrots, onions, parsnips, etc. just before the seedlings emerge from the ground. By using the flame weeder just before the plants come up, the fast germinating weeds are destroyed, and the carrots or other crops emerge into an essentially weed-free bed.
The best thermal weed control is achieved with a “stale bed”. This means that the soil is prepared and the rows marked for planting approximately 2 weeks before the crop is planted, to let the weeds start to germinate. In dry climates water should be applied to promote weed germination. Floating row covers can be spread over the beds to further speed up the germination of the weeds if the beds have not been prepared far enough ahead of time.
Then without tilling the soil again you plant into the “stale bed”. Plant either by hand or with a planter, trying to disturb the soil as little as possible. In this way, by the time the carrots are starting to germinate, the greatest number of weeds are already up to be killed by the flame weeder.
With some close observation one can find the right timing. A pane of glass placed over the row and sealed around the edges will create the greenhouse effect and cause the carrots in that part of the row to germinate more rapidly. When you see the carrots coming up under the glass you know that the rest of the row is about to emerge from the soil. When you think the crop is about to come up, it is good to dig several places in the row and inspect the sprouting seeds to be sure to get the right timing. We tend to plant the crops for flame weeding slightly deeper than usual, so that we have more leeway from germination to seedling emergence. First the seed starts putting down a root and then the seedling leaves start pulling out of the seed coat as the plant moves up toward the surface of the soil. This is the time to flame – just before emergence. It is better to flame a little too early than too late. With a little experience the right timing can be assessed quite easily.
Flame weeding kills some annual weeds for good, but perennial weeds often regrow from the roots left in the soil. Perennial weeds require several treatments at two to three week intervals. As with any weeding method, if you kill back the tops often enough, the weeds eventually give up and die.
A flame weeder setup consists of a wand connected to a propane tank by a hose. You’ll also need a dolly to carry the propane tank, and a flint igniter to light the flame if the wand doesn’t have an electronic starter. Read the instruction manual completely before using a flame weeder.
What is Flame Weeding?
The problem with flame weeding in gardens is that it’s hard to expose the weeds to the flame without exposing your plants as well. In vegetable gardens, use a flame weeder to kill weeds that emerge after you sow seeds, but before the seedlings emerge. You can also use it to kill weeds between rows.
Flame weeding works best on annual weeds that are 1 to 2 inches (2.5-5 cm.) high. Use flame weeders to kill weeds that grow around garden barriers and fences. They excel at killing weeds in sidewalk cracks, and you can even use them to kill stubborn, broadleaf weeds in lawns because mature lawn grass blades are protected by a sheath. Once you have a flame weeder, you’ll wonder how you ever got along without it.
Flame weeding entails passing a flame over a weed briefly to heat the plant tissues just enough to kill them. The goal is not to burn up the weed, but to destroy plant tissue so that the weed dies. Flame weeding kills the above ground portion of the weed, but it doesn’t kill the roots.