Cultural Measures
Mowing to the right height, as discussed in Reducing Lawn Maintenance, is one key to preventing weeds. In addition to promoting healthier grass, keeping your turf on the long side helps block sunlight from weed seeds just waiting to germinate. when weed seeds are evident, catch your grass clippings and dispose of them, rather than redistributing them on the lawn. Maintaining optimal fertility is also paramount, as a dense lawn makes it difficult for weeds to compete. Critical, too, is timing of fertilizer applications. Applying fertilizer in the summer to dormant northern grasses is a sure-fire way to energize any weeds present. On southern, applying fertilizer in the fall encourages cool-season weed growth. Fertilize northern grasses in the fall and southern lawns in mid spring. That will ensure strong growth as the grasses enter their main growing seasons. Another way to make your lawn inhospitable for certain weeds is to rectify compaction and poor drainage. Lastly, thwart the growth of shallow-rooted weeds by watering deeply but infrequently, and allow the top 1/2 inch of soil to dry out between irrigations.

Weeds are opportunistic plants, and sometimes ridding your lawn of them entails changing those conditions conducive to their growth. Areas compacted from frequent foot traffic, and therefore prone to growing plantain and crabgrass, might be better served by the installation of a walkway or stepping stones. If weeds congregate in the hard-to-mow areas under or adjacent to fences and walls, consider eliminating them by using edging and mulches. If a bare area should develop, don't leave it open to weed invasion; reseed as soon as possible.