Fumigation involves the use of gasses over a three-week period to treat weeds. Fumigation is expensive and best performed by professionals who know how to work with the highly toxic gas methyl bromide. If evacuating your plants to allow their bed to lie dormant for three or four months is not part of your gardening logistics plan, then the battle must be fought after weeds have already rooted. Aside from laborious plucking, the only post-emergence weed control method involves herbicides. Herbicides are categorized as systemic or contact chemicals.
Systemic herbicides kills every part of the weed from the roots to the tips of the leaves.
Contact chemicals kill only the above ground leaves and stems. For particularly stubborn weeds, contact chemicals are ineffective, as they do not affect the weeds' often vigorous roots systems. Weeds in gardens are best treated with commercial squirt sprayers that direct the chemical directly to the root. Again, weeds are nothing but misplaced plants, so hastily applied herbicides will not discriminate with the prize-winning Impatients. Weeds are as varied as plant species in general, but some appear to cause more consternation among gardeners than others.