The best time to seed a lawn with cool-season grasses such as bluegrass, fescue and ryegrass is late summer, Aug. 15 to Sept. 15. Nights are cooler (an aid to germination), the season is about over for most weed seeds to germinate, and the grass has more time to become well established before having to cope with hot, dry summer weather.

If you already have a lawn and it needs renovation, specialists recommend that you repair instead of starting a new one if 50 percent of the lawn is satisfactory.

It is suggested that you attempt to determine what caused the lawn to go bad and see if you can remove the primary cause of deterioration.

Don't start to work on your lawn if the soil is bone-dry. Wait until there is a good soaking rain. Watering with the hose may be satisfactory, but it must be done thoroughly, which means several hours.

Most soils in the East are too acid for best growth of lawn grasses. If you have not had your soil tested, University of Maryland specialists recommend application of 80 pounds of ground limestone per 1,000 square feet of lawn. Mix it thoroughly with the top 4 to 6 inches of soil.

Choose a blend of seed rather than just one variety. A good mixture would consist of Merion and Pennstar bluegrasses and Pennfine perennial ryegrass.

The reason for the mixture is that if a disease hits the lawn, it may affect only one or two grasses and the other will continue to provide a green lawn. Perennial rye germinates in a few days compared to three weeks for bluegrass and is as attractive and enduring as the bluegrasses but doesn't spread as they do.

Don't throw the seed down on bare, hard ground. Loosen or scratch up the soil so the roots can take hold and grow. The seed should not be completely covered with soil because it needs light to germinate. But it also needs to have good contact with the soil. If necessary, work some organic matter such as compost into the soil.

After planting, the seed bed must be kept moist. Sprinkle once or twice a day to moisten the surface until the seeds germinate. Then water less often but for a longer period of time in order to get the water down to where the roots are.

Begin mowing the new grass when it has grown to about twice its intended clipping height. Mowing encourages branching from the crown. A few weeds may show up, but they offer little hazard in autumn.

After you have mowed twice, fertilize the lawn. Apply 30 to 40 pounds of 5-10-5 fertilizer per 1,000 square feet when the grass is dry, and then water it in with the hose.