The most commonly accepted definition of a weed is a plant growing where you don't want it. Corn growing in the zucchini patch might be considered a weed. Weeds growing in the vegetable garden are undesirable, but weeds growing on hills prevent erosion and strengthen soil structure. Familiar vegetable garden weeds include crabgrass, pigweed, morning glory and ragweed. Weed killer methods are organic or chemically based practices.
Weed killer products are herbicides designed to eradicate germinating and mature weeds. Excessive weed growth diverts water supplies from vegetables and can choke vegetable roots. Weeds may serve as hosts for undesirable insects and disease organisms. They may be poisonous to livestock and cause impurities in agricultural products. Weeds also cause allergic reactions in some people.
Weeds in vegetable gardens compete for soil nutrients, sunlight and water. Weed control in large-scale agricultural operations is related to economic viability. Livestock that grazes on wild onion or garlic produce milk with an offensive odor. Wool that contains burs from weeds is less valuable because of the expense of removal. Weed control issues are vital to successful farming and gardening.
The University of California Davis Sustainable Agriculture Research and Education program recommends the use of cover crops to control weeds. Crops such as vetch, clover, and alfalfa are grown in between crop rows. Cover crops suppress damaging weeds, add nutrient content to the soil and provide green manure when cut to harvest. In home vegetable gardens, cover crops such as thyme or parsley can be grown between rows.
Roundup weed killer is the most commonly used chemical herbicide both industrially and for home gardens. It is a nonselective herbicide that destroys growing weeds. A 2009 study at the University of Caen, France concluded that there is a significant health risk to women and men associated with the use of Roundup. The "inert ingredients" not listed on packaging have been shown to be more damaging to health than its main ingredient, glyphosate.
"Prevention is the best medicine" for weed control, according to the Capitol District Community Gardens. Prevention techniques include mulch, hand weeding and hoeing weeds once they have sprouted. Weeds germinate in early spring and set their seed heads in autumn, so prevention techniques are best applied at those times. Garden centers supply hand-held weeding tools that are very effective in pulling out weed taproots.