Weed identification and control can be a difficult task. Each region of the world, including the United States, can produces different weeds, each with their own control method. There are some general classifications that most weeds fall under, which can help you determine the weeds in your lawn or garden.
Most weeds fall under three classifications: grasses, sedges and broadleaves. Grasses are short plants with long, narrow leaves. The grass in your lawn, in some areas, may be considered a weed. Sedges are grass-like in appearance but have triangular stems and produce small, inconspicuous flowers and are usually found in wet ground. All other weed varieties fall under broadleaves, due to their wider leaf structure.
Weeds are classified further by their growing styles. Summer annual weeds grow every spring or summer from a new set of seed, as the previous year's weed has died off. Winter annuals bloom in the fall or winter from seed, as well. Biennial weeds grow at any time during a growing season and survive until the next growing season. Perennial weeds come from seed or by a vegetative part of the plant taking root, but stay in place for two years.
From these basic categories most weeds can be identified according to the shape of the leaf, any flowering, any apparent rhizomes and the geographic region. If weed classification is still proving to be difficult, samples of weeds can be taken or sent to a university extension office for identification.
Cultivation control is the method of weed prevention when planting grass or vegetation. This is one of the most effective methods of control. Planting seeds that are nearly weed-free will prevent new plants from springing up. Mowing of a lawn, or physical removal of weeds before they begin to flower, will also prevent the spread of weeds throughout the yard.
Weeds can be controlled by the application of herbicides. Different weed varieties react differently to certain herbicides, so it is important to try and identify the weed before applying any chemicals. Herbicides are available which kill most varieties, but these are often so non-specific that they can kill desired plants if mishandled. Selective herbicides will attack weeds only. Pre-emergence herbicides are also available; they attack weeds before they begin to sprout from seed.