Soil for Shaded Lawns
As with lawns anywhere, the quality of the soil is of great importance in shaded areas, even more so than in sunny places. It must not pack down and become pasty and "puddled" under the influence of heavy drip from leaves and branches. If it does, air cannot enter and grass roots die.

If the soil is sandy or gravelly, packing will not occur. Heavy, clayey soils are particularly subject to packing and should be protected against it when the ground is first made ready for seeding. The upper three or four inches of earth should be mixed with very liberal amounts of coarse sand, grit, or gritty coal cinders, as well as organic matter such as peat moss, compost or commercial humus. One-third part by bulk in the upper soil is not too much if the soil is clayey. In very heavy (clayey) soils more may be used.

Soil under trees may become excessively acid or in other ways toxic to grass as a result of substances formed in leaves that are washed into the ground, and in some instances, it is suspected, roots may give off harmful substances. Walnut trees have long been believed to bring about conditions inimical to the growth of grass and other plants. Turf cannot usually be persuaded to grow beneath well-established conifers (narrow-leaved evergreens), such as pines, firs and spruces. If possible, it is better to leave the fallen brown needles (leaves) as ground cover in such places. These look attractive and
form a natural mulch that keeps the roots cool and reasonably moist.

Toxicity (poisoning) of soil is most likely to occur where subsurface drainage is so poor that the ground lies wet for long periods. This is especially likely to happen in winter and early spring. As a result of the wetness, soil bacteria, necessary for the proper development of grasses, do not prosper and cannot play their part in creating favorable soil conditions. Spiking with an aerating tool or machine helps drainage to some extent, but if conditions are extreme, an installed drainage system is the only answer.
If a soil test shows that the ground is excessively acid, apply lime, but don't do this as amatter of general principle without ascertaining that lime is indeed needed. Be careful not to use it around azaleas, rhododendrons or other decidedly acid-soil plants.

Tree Roots
In many shaded places roots of trees and shrubs pervade the ground. Naturally they take up water. If they are near the surface they are in immediate competition with the grass for moisture, but even the deeper roots absorb moisture that might rise in the ground by capillarity (in the way oil travels up a lamp wick) and be useful to the grass if the tree and shrub roots did not get it first.

But that is not the whole story. While the roots of trees and shrubs take water from the soil, the shade of their branches and leaves checks loss of water from the surface soil by evaporation. This gives the gardener something of a break early in the season, but he pays for it later.

Until the spring is well advanced and early summer is at hand, shaded areas are less likely to dry to the extent that they need watering than are sunny ones, but after that wow! watch out. A week or two of really dry weather and the grass under trees will surely suffer if you fail to irrigate it.

Grasses for Shaded Areas
If the lawn-to-be will receive at least two hours of direct sunlight or its equivalent in dappled sunshine (very light shade with sun filtering in through for most of the day) ordinary grass mixtures intended for sunny places are satisfactory, but in places more densely or consistently shaded use blends of special grasses.

The great shady lawn grasses are Chewings fescue, Illahee fescue, rough-stalked bluegrass and velvet bent. Redtop and meadow fescue are temporary "nurse" grasses. In the South, St. Augustine grass and centipede grass are useful in shade and so is zoysia.Where shade is so heavy that even with the best care the grass plants are weakened to the extent that many do not live more than one to three years, you may be able to maintain a fair stand of grass by lightly reseeding each fall.

Don't allow fallen leaves to accumulate on the lawn. These cause additional shade and so further reduce root growth, thus weakening the grass. If allowed to mat down, they encourage disease and dying of the grass in a pockmarked pattern.

Avoid mowing grass in shaded areas too closely. The leaves of the grass are factories that convert simple elements absorbed by the roots from the soil and by the leaves from the air into complex tissue-building foods. These foods strengthen the grass plants. Because the foods are less abundant when the leaves are closely cut, this practice weakens the grass. During hot summer weather a cutting height of two to two and a half inches is best for shaded lawns; in fall this may be reduced to one and a half inches.

Water and Fertilizer
As with lawns anywhere, when water is needed, give enough to penetrate to a depth of at least six inches, then no more for several days, perhaps four or five days in hot weather in areas where tree roots abound. The water should be applied in a fine spray.

Grass growing in the shade of trees and shrubs has to compete with them for food as well as moisture. Relieve the pressure of this competition by providing for the needs of the trees and shrubs as well as the grass. Fertilize the lawn regularly and also the trees and shrubs. So far as possible, place the fertilizer intended especially for the trees and shrubs deep in the soil so that their roots are encouraged to strike downward.

For the grass two substantial feedings a year are normally sufficient. Apply one in early spring and one in early fall, after the really hot weather of summer has passed. If the soil is known to be infertile, a third feeding in early summer is beneficial, but I do not recommend this on rich soils because excessive fertilization, particularly during hot weather, is liable to harm grass by making available more nitrogen than it can use. This may make the grass susceptible to disease.

An annual topdressing of sandy soil, organic matter and fertilizer, applied in spring, not only provides the roots of the grass with nutrients but, by adding humus and replacing surface soil that may have washed away, serves as a cushion to break the weight of falling drops of water that cause soil compaction.
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