Trying to grow grass under a large tree can be a frustrating experience. Yet, it may be possible to do so to a satisfying degree eight or nine months out of the year if the tree is one of those that loses it leaves in the fall.

The big problem, of course, is how much shade the tree casts and how much competition the grass will get from the roots of the tree. An oak tree, with no low branches, should let enough light through to allow the grass to grow fairly well provided the right kind of grass is used and it is given the proper kind of care.

A Norway maple or beech is difficult, if not impossible, because of dense shade and too many tree roots near the surface. But even here something may be accomplished.

When the tree starts to lose its leaves in the fall, seed the area under it with perennial ryegrass. In a week to 10 days the grass will be up and growing. Given moist ground and a little warm weather, the new ryegrasses make a green carpet in just a few days.

Some of the very good new ones include Citation, Diplomat, Manhattan, NK-100, NK-200, Pennfine and Yorktown. They are far different from the ryegrasses of yesteryear. They not only look as good as blue grass, but withstand climate extremes much better than common perennial ryegrass.

They may need mowing a day or two sooner, otherwise they are hard to tell from bluegrass. The foliage is a little shinier and may turn tan a bit earlier in winter.

In the spring, keep the ryegrass watered and fertilized, don't mow it too close and it should stay nice and green well into the summer and maybe even longer. In the fall, when the tree leaves start to fall, seed the area and start all over again.

How on the ryegrass will persist, of course, will depend on the degree of shade and the number of tree roots.

The most important effect of shade is the reduction of light intensity. A canopy of trees can screen out as much as 98 percent of the incoming solar radiation. The light quality under a canopy of trees has a spectrum low in blue and red wavelengths and these are the ones necessary for photosynthesis (food production).

The root system of shaded grass plants usually is shorter, thinner, wiry with fewer branches. Under a tree there is increased relative humidity and dew and a reduction in wind movement. This provides a very favorable microclimate for turf disease activity.

In preparing the seed bed for the ryegrass, most of the small tree roots can be removed from the top three or four inches of soil. It is risky to cut off the larger roots. It might affect the anchorage of the tree.