Brown patches on a lawn are an eyesore. But that's not the only reason they need to be addressed. Brown spots make the lawn vulnerable to weeds, which may eventually take over if the problem continues. More importantly, brown spots are often a sign of a larger problem with your lawn that needs to be identified and remedied before any fix will be effective.
Identify the Problem
Reduce nitrogen levels in your lawn. If your lawn is sporting brown patches because of excess nitrogen due to over-fertilization, the patches will be quite large. To fix the problem, wait one month for the nitrogen to leach out of your lawn, switch to an organic fertilizer (like grass clippings) and then re-seed.
If your lawn's excess nitrogen is due to your pets (or the neighbor's pets) using it as a toilet, the brown patches will be in their favorite spots to visit. Water the spot thoroughly with a hose to wash away the nitrogen and the grass will eventually grow back on its own. If the grass does not return, re-seed.
Limit foot traffic. Brown patches that are a result of foot traffic usually look more like paths. To fix this problem, aerate your lawn. The grass is dying because the traffic has compacted the soil and it is no longer allowing oxygen to the roots. You can either hire someone to professionally aerate your lawn, or stab a garden fork into the ground at regular intervals to let the oxygen in. Then re-seed and create a stone pathway through the area to direct traffic.
Water the lawn less frequently. In an over-watered lawn, brown patches often occur in areas with poor drainage. The next time you water, check for any spots with standing water. Determine the cause of the drainage problems. Fill in any holes or depressions, or add drainage tiles or pipes in wet areas. Once you have fixed the drainage problem and your lawn has dried out, re-seed.
Treat your lawn with fungicide. Sometimes brown patches are due to a fungus appropriately nicknamed Brown Patch. Lawns suffering from Brown Patch will form small, circular brown patches that quickly expand into brown rings when the weather starts to heat up. To properly diagnose your lawn's condition as Brown Patch, call your county Extension office for a correct diagnosis. Once Brown Patch is identified, a simple fungicide and a little re-seeding will fix the problem.
Let there be light. If brown patches occur in a part of your lawn that is always shaded, your variety of grass may need more than the available light level to grow. To fix the problem either move the offending object, continually re-seed the area or replace that patch or the entire lawn with a variety of grass that is more tolerant to shade.
How to Re-Seed the Lawn
Use a hand cultivator to loosen up the top three to four inches of soil.
Follow the seed manufacturer's instructions for seeding. Sprinkle fertilizer over the cultivated patch and then sprinkle the grass seed over the patch.
Cover the patch with a layer of compost and tamp the area with your foot.
Water the patch daily until the grass is two inches high. Then water the patch every other day until the grass has matured.