How to Overseed a Lawn During a Cool Season

Overseed the lawn when temperatures in your area drop to the low-to-mid 70s F, if you don't have access to a cooperative extension in your region. To give it a good start, apply a starter fertilizer when the seedlings begin to sprout. High levels of phosphorus and potassium are needed to develop the root system. Use a 5-10-10 or 10-20-20 fertilizer to apply 1/2 pound of nitrogen per 1000 square feet. Apply a slow-release fertilizer --- 12-4-8 or 16-4-8 --- again in November and February.

Mow the lawn area before overseeding. Rake the grass to remove all debris. Using the grass catcher attachment, mow the lawn shorter than you normally would, but not at the lowest level. For St. Augustine grass, mow no lower than 3 inches. After mowing, rake the lawn again to remove lingering grass clippings and any debris that got kicked-up by the mower. If your grass was extremely long to start off with, you may need to mow and rake again.

Dethatch the lawn area. Thatch consists of undecomposed plant material close to the soil, such as dead grass, weeds and roots. It forms a mat of tangles that prevents the grass seed from contacting the soil and chokes out the living grass. Dethatching requires a power vertical mower or power rake. You can rent a dethatcher and broadcast spreader at a rental shop that carries yard equipment.

Dispense half the seed by pushing the broadcast spreader along the yard either horizontally or vertically. Dispense the other half by pushing the spreader diagonally across the yard. Take a stiff broom and, using short strokes, sweep back-and-forth in a cross-hatch manner in small sections at a time. This prevents you from sweeping the seeds into a pile, leaving patches of soil unseeded.

Water your newly seeded lawn. The ground must stay moist in order for the seeds to germinate. Once or twice a day, spray your lawn area lightly for 10 to 20 minutes until the seeds germinate. It typically takes seven to 10 days for germination. Continue to water 1/4 inch a day for two to three weeks until seedlings are well established. After several mowings, you can water the well-established lawn as needed.