Late summer is unquestionably the best time to repair a lawn or start a new one. Sodding can be done successfully almost any time of the year if the weather permits. Seeding bluegrass in the spring can be hazardous because it takes so long for the seed to germinate and unless the grass is fairly well established before hot weather sets in, it is in trouble.

Some of the new varieties of perennial ryegrass if kept moist and temperatures remain moderate, can show a fuzz of green in a week, certainly within two weeks, according to Dr. Robert W. Schery, director of the Lawn Institute. A new seeding of perennial rye looks like a lawn within a month while slower-growing species may not really shape up until the second growing season.

The color of the new perennial ryegrasses (which includes Manhattan, NK-100, NK-200 and Pennfine) is an attractive dark green; often the new ryegrasses are mixed with improved bluegrasses to encourage long range sod formation.

Grass seedlings that come up early in some normally shady areas have a chance to benefit from extra sunlight before leaves are out on the tree. They also have a head start on any weeds that may be in the lawn.

Seed may be put down as early as convenient. When the weather finally warms up so that soil temperatures are 55 to 60 degrees F., the temperature range at which seeds begin to germinate, the new grass seed will be ready to start growing.

Don't throw the seed down on the bare ground. To get really good results there must be cracks or crevices in the soil. The seed need light to germinate but also must be in good contact with the soil for roots to become established.

Do not let the ground dry out once the seed have germinated. The delicate new sprouts must stay moist. Frequent light watering, as much as two or three times per day, is the key. In this early stage, long or deep watering is not necessary, and may even dislodge some of the new seedlings. Just keep the ground moist until the plants are established.

Light quality under trees is severely altered by the fact that the leaves absorb the majority of the photosynthetically active wave lengths of light, according to specialists. The light reflected or transmitted to the turfgrass plants below is predominantly from the green, yellow, and dark red regions and is not of high photosynthetic quality.

The tree canopy tends to moderate daytime temperature fluctuations and prevent cooling at night. It prevents evening reradiation of the long wave lengths of heat energy to the air. The shade lessens the extremes of temperature found in full sun.

This moderation helps humidity remain high in shaded environments both day and night. In densely shaded areas where both shrubs and trees are present, wind movement is often severely restricted and stagnant layers of humidity and constant temperature will exist. This constant temperature and humidity in the presence of sundued light creates conditions conductive to fungus proliferation.

The grass response is succulent, thin-walled leaves which are heat, drought and disease susceptible. The reduced sunlight leads to decreased carbohydrate reserves in the turfgrass plant, and the plant is less able to heal from injury created by traffic, or plant pests.

Judicious pruning and trimming of trees will increase the chances of survival for the grass. Removal of low hanging branches to a height of 8 to 10 feet improves air flow and light penetration. When low hanging shrubs are a part of the landscape design, English ivy or pachysandra should be planted.

Tests at Michigan State University showed that reduced light intensities resulted in poor quality grass but the grass would have been fairly decent except for disease attacks.

For example, powdery mildew seldom does serious damage to Merion bluegrass in full sun but can ruin the grass in a short time in a shady situation.

The fescues are the best grasses to try in a shady situation, including Chewings, Pennlawn and Kentucky 31. But if there is less than two hours of sunshine daily and heavy shade the rest of the day, the grass won't last long.

Most lawn grasses grow best in moderately to slightly acid soils, ph 6.0 to 6.9. The only way to find out about your soil is to have it tested. In almost all states a soil test is available at the state university. For information on how to take the soil samples and where to send them, phone Cooperative Extension Service, listed under your County government, or write to the state university.