The best defense is to keep your lawn healthy by fertilizing and topdressing with organic material once a year. Mow your lawn correctly and aerate it periodically to discourage thatch buildup and soil compaction.
Even with the best care, bare, thin, or weedy patches occasionally develop in certain areas. Deal with these problems as soon as possible so the damage doesn't spread. Weeds rapidly will fill in bare areas if you don't populate that space promptly with new grass.
Repairing a lawn problem is a two-step process. First, try to determine the underlying cause. Sometimes an accident, such as a fertilizer spill, creates a bare spot in the lawn. Or the cause might be chronic disease, destructive insects, or competition for light and moisture from overgrown neighboring plants. Correct these deficiencies first, or your repair efforts will be futile.
Give a thin, tired lawn new vitality and disease resistance by over seeding it with new grass seed. In northern states, do this in the fall, so the cool-season grasses have time to develop strong roots before they have to face summer. In southern states, repair lawns of warm-weather grasses in the spring by sprigging or plugging -- these grasses need warm weather to grow well.

Regular fertilization gives grass
plants consistent uniform nutrition
for at least two or three months.

Step1

1. Mow the existing grass as closely as possible; be careful not to scrape the crowns of the plants. Remove the clippings to expose bare soil, so the seed will have direct contact with the soil.

Step 2

2. Use a garden rake to rough up the soil between the grass plants. This, and the stubble of the freshly mown grass, will make a good seed bed for the new seed you're adding.

Step 3

3. Sow seed at the rate recommended for new lawns. This compensates for reduced germination as some seed falls into existing grass, not on the soil.

Step 4

4. Roll the area lightly. Topdress it with topsoil or compost (optional). Water frequently. Mow the new grass when it reaches 3 inches in height.

Step1

1. Delineate the spot you'll be repairing by digging around its border. Remove and discard any poor grass and weeds within the area. Keep the remaining bare soil free of debris.

Step 2

2. Invest as much time and effort in preparing the soil in this small repair area as you would for an entire lawn. Dig in organic matter and granular, slow-acting fertilizer. Rake the soil smooth and level.

3. Sow seed thickly. Use a variety that corresponds to the surrounding grass if possible. Otherwise use a mixture of grasses appropriate to the region.

Step 3