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Home  > Question of the Week

Question of the Week

Permalink What can you tell me about flame weeding as a method of weed control in organic crops?

Answer: Flame weeding is a non-chemical weed-control technique common among organic farmers. Flame weeding, also referred to as flame cultivation, often uses propane gas burners to produce a carefully controlled flame that briefly passes over weeds. The intense heat blanches the leaves, causing a disruption within the plant’s cell walls. Flamed weeds usually wilt and die anywhere from within a few minutes to a few days after flaming. One quick way to check to see if the plant foliage has been adequately flamed is to see if a thumb print is retained on the leaf when pressed between your thumb and finger.

Weeds are most susceptible to flaming when they are one- to two-inch-tall seedlings. Broadleaf weeds are more susceptible to flaming than grasses as grasses develop a protective sheath by the time they are approximately one inch tall. Therefore, grasses may require a second flaming. Repeated flaming can also be used to suppress perennial weeds such as field bindweed. Flame weeding is commonly used in the stale seedbed method, which involves allowing weeds to grow in order to be killed by the flame (or other method). This method is usually repeated prior to planting a cash crop as another flaming may be used after planting and before germination of the cash crop.

Flaming on dry, sunny days is recommended as any moisture can give the plants some resistance to the heat. For larger areas, working in sections can help establish effective fire breaks, particularly when flaming dried material, such as stubble, as it can ignite. Green plants usually do not ignite when treated with a flame.

Most flame weeders are designed to not radiate large amounts of heat. Their purpose is to sear the leaves of plants (weeds) in order to change the protein structure of the plants. As a result, stress kills the weeds, not the torching of them. Due to the design and purpose of flame weeders, there is no soil disturbance and generally not enough heat is produced to penetrate the soil and effect soil life. As stated above, timing is everything.

There are several different designs commercially available for tractor-mounted flame weeders. Some flame weeders burn propane in the gas state, while others burn gas in the liquid state. It is important to note that tractor-mounted tanks should be rated for “motor fuel” as they will be mobile and not stationary. Another design difference is whether the gas flows directly from the tank to the burners, or is distributed through a manifold first. In addition, the burners may be fixed or adjustable, with the latter offering the ability to adjust the position of the flame. Having individual shut-off valves for each burner provides flexibility in using a flame weeder so that the flames can be directed or broadcast over an area. Flame weeders are available with different BTU (British Thermal Unit) ratings.

In addition to weed-control benefits, flame weeders can also be utilized for other applications. According to some resources, potato plants up to eight inches tall can be flamed to kill Colorado Potato Beetles, Leptinotarsa decemlineata, without causing undue damage to the potato plants. Flamers can also be used to incinerate fallen fruit and mulch.

For more information on flame weeding, see ATTRA publication Flame Weeding For Vegetable Crops, available at

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Permalink What are some nitrogen-fixing fruit trees that I can incorporate into the alleyways of my citrus orchard in central Florida as a permaculture method?

Answer: Worldwide, about 650 tree species are known to be, and several thousands are suspected to be, nitrogen fixing, according to the World Acroforestry Centre. For more information, see

Here is a list of nitrogen-fixing trees that should be suitable to your zone ("sub-tropical" with lows of 25 to 30 degrees F):

Acacia—some species
Leucaena—Leucaena leucocephala produces edible pods and is native to Mexico and Central America
Pongamia—Millettia pinnata has marginal hardiness and is being grown around Miami
Cassia—Cassia spp. will tolerate short-lived frosts
Carob—Ceratonia siliqua is native to the Mediterranean and might not tolerate the wet periods of central Florida
Honey locust—Gleditsia triacanthos is popular in permaculture though its nitrogen-fixing ability is disputed
Rosewood or tipu tree—Tipuana tipu
Albizia (mimosas)
Moringa—Moringa oleifera, the most commonly cultivated species of moringa, is native to India and the leaves and seed pods are used as food.

However, of these, only carob is really commonly used for its "fruit." Moringa, though, is widely used for its highly nutritious leaves.

These are trees that are or have been used by permaculturists as recorded in the writings of Bill Mollison and David Holmgren. Here's a link to a great chart of (mostly) tropical leguminous trees used in permaculture:

If you’re not too attached to the fruiting aspect, it does appear that there are several good candidates for nitrogen-fixing leguminous trees in the alleyways of citrus plantings. A word of caution, though: many of these species are extremely fast-growing under the right conditions and may be considered invasive pests in certain areas.

For brief descriptions of the taxonomy, ecology, characteristics, and management of over 50 multi-purpose trees used in agroforestry and intercropping systems, including over 30 nitrogen-fixing species, see the list at The trees on this list are mostly, if not exclusively, native to the tropics and/or subtropics.

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Permalink My mature chestnut trees don’t produce full-term, filled-in nuts. What could be the problem?

Answer: After consulting with chestnut experts in California and Florida, as well as delving into the published research, all sources seem to point to a pollination problem. However, since chestnuts are pollinated by both insects and wind, it is unlikely that having no pollinators is the problem.

Rather, cross-pollination is likely the problem. But the experts agreed that your three different species should solve this unless there is a noticeable "asynchrony" in bloom time (meaning they don’t bloom at the same time). Even then, the fact that you have three different species and several different varieties should render that idea irrelevant.

There is no sense in going out and buying another tree because it would take too long for it to come into flowering. However, you mentioned that there are other chestnut trees in the area that produce nuts that fill out. During this coming spring’s bloom period, make contact with the owners of those other trees and take "bouquets" (prune some blooming twigs off), put them in a coffee can or something similar, put some water in the can, and hang these in the trees. Try to make six to 12 of these hanging bouquets and try to take them from different trees. Isolated pear trees have been made to bear fruit this way, and this technique might work for you.

If it does work and you get filled shells after doing this, then you at least know the problem is cross-pollination and then it might make sense to try to bud or graft some of your neighbors' trees onto small limbs of your trees, or buy yet another tree.

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Permalink My four-year-old blueberry bushes are planted in a wet, shady location. Should I move them to a drier, sunnier spot?

Answer: You should consider moving your blueberry bushes if they appear unhealthy or drought-stressed or if they are too far from the house to be managed effectively. This includes being able to water them frequently as they begin fruiting because they are about the right age to begin production.

If they appear healthy, they are close enough to the house to be managed effectively (including irrigation as they begin full production), and, with a minimal amount of clearing work, you can ensure their continued survival, you probably don't need to move them.

Moving established blueberry bushes of this age is surprisingly successful. If the bushes were planted correctly and the planting hole contains a lot of peat moss, the roots should not be that extensive and transplanting should proceed relatively easily, though it is important to get as much of the root mass as possible.

Be sure to transplant the blueberry bushes during dormancy. You will also probably want to cut back or thin out a lot of the little trunks to help minimize transplant shock (some root loss is inevitable during transplanting, and so the tops need to be brought back into balance with the roots). You may delay or reduce fruiting during this transplant year.

If you choose not to move them, be sure to provide them with good management practices as described in the ATTRA publication Blueberries: Organic Production, available at

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Permalink My goats and llamas have overgrazed my small pasture, which contains several bare spots and plenty of knapweed and leafy spurge. How can I continue to irrigate the pasture and also help prevent further deterioration?

Answer: You could try a red and white clover mixture to frost seed into your existing irrigated pasture. Try sowing one to two pounds of each type of clover the first part of March. It is best if you graze off the grass to a couple of inches or so before you seed. Sow the seed before you turn the goats out and let them tromp it into the soil. You can use your electric nets to concentrate the goats in a small paddock and move them accordingly. This will get the seed in contact with the soil. You'll need to keep the goats off the field until the clover has grown up enough so you cannot pull it easily it out by hand— you don't want your goats to pull it out by the root when they are grazing it.

Goats will eat knapweed and leafy spurge readily. You can fence your goats in with one of your nets, let them graze the knapweed and spurge down, and then move them to an adjacent paddock that you make with another net. You don't need to graze the weeds down to the ground; in fact, it is preferable if you just take the flowers off and then move the animals. This will let your overgrazed grass have a chance to come back. Graze the weeds whenever they flower during the summer and, after two to three years, you will notice a serious decline in those noxious weeds.

In order to preserve your grass stand, always let the grass fully recover between grazing events. You can tell if a grass is fully recovered with this simple trick: follow an individual grass stem down to its base. If the lowest leaf right near the ground is either brown or has a brown tip, that grass has recovered from the last time it was grazed. This is a simple management procedure that too few graziers employ and it is the most important procedure in all of grazing. By letting plants recover, you will make it easier for them to make it through the winter, have healthier stands and healthier soil. In general, it takes about four to five weeks for a grass plant to recover, depending on the species.

Another practice you can employ to help your grass stand is to move your goats out of their paddock they are grazing when the grass is still six inches or so tall. Do not let them eat it down beyond that if you can help it. This leaves some "solar collectors" still intact on the grass plant and it can readily begin to start growing back. That way, it does not have to rely on stored carbohydrates to start its growth again. This will contribute to the overall health of your grasses in your pasture.

See the ATTRA publication Irrigated Pastures: Setting Up an Intensive Grazing System That Works for more information and beneficial grazing strategies. It is available at

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