Cultural Measures Count
In addition to promoting healthier grass, mowing to the right height is helpful in preventing weeds because keeping your turf longer helps block sunlight from weed seeds waiting to germinate. When weed seeds are evident, catch your grass clippings and dispose of them, rather than redistributing them on the lawn. You should make sure to maintain optimal fertility, since a dense lawn makes it difficult for weeds to compete. The timing of fertilizer applications is also critical.
Do not apply fertilizer in the summer to dormant northern grasses, because it is a sure-fire way to energize any weeds present. Fertilize northern lawns in the fall.
Do not apply fertilizer in the fall, beacause it encourages cool-season weed growth. Fertilize southern lawns in mid-spring to ensure strong growth as the grasses enter their main growing seasons.
Another way to improve your lawn and make life for weeds inhospitable is to correct compaction and poor drainage. Weeds are opportunistic plants, and to rid your lawn of them you must change the conditions conducive to their growth. Consider installing a walkway or stepping stones in heavy foot traffic areas to eliminate plantain and crabgrass. For hard to mow areas (under or adjacent to fences and walls) try using edging or mulches to prevent weeds from taking root. You should also reseed bare areas as soon as possible. Lastly, thwart the growth of shallow-rooted weeds by watering deeply but infrequently, and allowing the top ½-inch of soil to dry out between irrigation.