A new lawn of cool-season grasses can be started or an old repaired almost any time between early spring and mid-fall. But the best time is late summer (mid-August to mid-September) and the next best time is early April.

It takes know-how and careful attention to details to succeed during hot weather. The main problems are moisture and weeds. The soil dries out rapidly and must be sprinkled lightly and gently three or four times a day because if the seed do not have adequate moisture after germination starts, they die.

Weed seed are almost certain to be present in the soil and they germinate quicker and are more competitive than the grass.

Cool-season grasses are the bludgrasses, fescues, bentgrasses and rye which ate at their best during cool weather.

The best time to plant warm-season grasses such as zoysia, St. Augustine and Bermuda is mid-to-late spring.

Sodding can be done successfully during spring, summer and early fall but late summer and early fall are probably the best and easiest times.

Weather conditions in late summer and early fall generally are better for germination of seed of bluegrass and fescue. The new grass has a longer time in which to become established before having to experience hot, dry summer weather.

In late summer, crabgrass and most other weeds are near the end of their growth cycle for the year and fall-planted grass has time to develop a good root system before having to compete with them.

The first decision is whether to do the whole lawn over or just patch it up. If you have grass fairly well distributed over 50 per cent of the lawn, it is probably better to repair than start over.

Try to determine why there are bare spots. Seeding or sodding bare sports will not be a permanent remedy unless the cause can be removed.

A femal dog can cause bare spots. In such a situation, the old soil should be removed to a depth of three of four inches and replaced with good soil.

Mowing the grass too close (less than 1 1/2 to 2 inches) can be harmful. Bluegrasses grow best in slightly acid soils and the soil may be too acid and in need of lime. The best way is to have your soil tested.

Hard-packed soil could be the problem. Heavy foot traffic, particularly when the soil is wet, can cause compacted soil. Compacted soil can be improved by misxing peat moss or compost with the top six inches.

If there is constant heavy traffic in a particular area, maybe a hard-surfaced walk is the answer.

Don't waste seed by just throwing them on and hoping Mother Nature will do the rest. First get rid of the weeds. Use an iron rake to scratch up the soil. If the seed are covered to the point they don't get light, they may not germinate. One the other hand, unless most of each seed dries out rapidly and may perish.

A seedbed free from competing vegetation, either old grass or weeds, offers a new seeding its best chance for success.

There is a lot to be said for sodding instead of seeding. Although it costs two or three times as much, it has a better chance of success, it can be installed in a matter of hours and used within a couple of weeks.

A seeded lawn, however, may have to be reseeded several times before it successfully takes root, with costs mounting each time.