Flame weeding is a very efficient way of weeding for organic growers. It is possible to flame weed around tougher plants like garlic and onions and before emergence of crops like cilantro and carrots. We have found that even more "fragile" plants like lettuce can handle flame weeding. At the HRC, we have used flame weeding specifically for our garlic and pumpkin patches.
Annual weeds are ideally flamed when very small, less than 2" tall. Flaming can impact perennial weeds as well if done repeatedly by depleting the carbohydrate reserves of the plant. There is no need to burn the weeds, just wilt them. Their color will change to a darker green after flaming and if you can press you fingerprint into the leaf you know have hit them with enough heat to kill them.
All that is needed to flame weed small acreages is a 20 lb. propane tank, a backpack frame (ours has a milk crate attached to it to hold the propane tank) and a propane burner. A variable squeeze valve allows you to vary the flame size and is a convenient feature. It is important to wear appropriate protective clothing when applying the flame and take care to avoid igniting dry areas surrounding the field! Make an effort not to expose the plants of interest to too much heat, walk at a steady pace and aim the flame between the plants and in the aisles.
Other Sources of Information About Flame Weeding
See our 2004 Garlic Study for a comparison of hand weeding and flame weeding in garlic. See also the 2002 Grower Grant study involving Flame and Steam Weeding in Strawberries. ATTRA (Appropriate Technology Transfer for Rural Areas) has a web page on Flame Weeding for Vegetable Crops. WSARE (Western Sustainable Agriculture Research and Education) also has a web page dedicated to Hot Tips for Flame Weeding.