In the Northeast, certain varieties of grass do not grow as quickly or as thickly as they do in the south. Homeowners, in an attempt to encourage growth, often apply more than the recommended amount of fertilizer. When that happens, the excess salt in the over-application of the fertilizer leaches all of the moisture out of the soil. The result is "burn" or brown patches in the lawn. Fertilizer burn is relatively easy to fix; but the best long term remedy is to make sure that it doesn't happen again. Get to know the nitrogen needs of the variety of grass that you have planted and do not exceed that limit.
Water the grass heavily once a week. Give the lawn at least 2 inches of water as soon as possible after over-fertilization. Washing the excess fertilizer away in time may re-vitalize some of the brown spots in a few weeks or keep other spots from turning brown. Continue to water heavily for one month.
Cut the lawn down to 1 inch in height.
Rake the lawn to clearly expose the holes and remove any debris.
Excavate the brown patches with a spade. Be sure to remove the blades and at least the inch below to get rid of the seeds.
Fill in the holes left by the removed grass with a quality top soil.
Spread a half-inch layer of topsoil over the entire lawn.
Choose a high-quality seed to overseed the lawn with. In the Northeast, varieties of fine fescues or perennial ryegrass work best. They germinate quickly, allowing them more time to establish themselves before the harsh winter. And they only need one application of fertilizer per year, which allows fewer opportunities to accidentally burn them.
Spread the grass seed over the lawn with a broadcast spreader. In general, grass seed should be spread at a rate of 1.5 pounds per 1,000 square feet. However, check the application rate of the variety of grass that you plan to spread.
Walk over the lawn to ensure that the seeds come into close contact with the soil.
Lightly water the grass three to four times per day until the new grass reaches 2 inches in height in a few weeks. Then go back to your regular watering schedule.