Trees can endure significant additions of soil where the grade line is above the original ground line only if wells are built around them. More than a 6-inch layer is hazardous without such a well. Wells are built of brick or stone from the original soil surface to the top of the new grade. The upper rim of the well is made level and is flush with the new grade only on the upper side of the slope. Wells are about 6 feet in diameter for mature trees. If the new grade line is no more than about 16 inches above the original, the well alone is enough to aerate the roots while they are being reestablished. If the added soil is deeper than that, a layer of coarse rock fragments, covered with fine stones and topped with some gravel and sand, should be laid outside the well on the ground out to the tips of the branches before the new soil or soil material is added. With tile laid through the well into this coarse layer, the roots can get air during the several years needed for the trees to establish roots in the new situation.

Having prepared the subgrade in even, gentle slopes, it should be firmed so that fills will not settle after the lawn is established. If the material is acid, ground limestone should be added. It can be fertilized on the basis of a soil test, but usually 30 pounds of ordinary superphosphate and 10 pounds of potassium sulfate to 1,000 square feet will not be far wrong. Manure, compost, or other organic materials should be worked into the subgrade material if it is clayey or if the soil tends to become massive.

After the subgrade is well prepared, the topsoil, already saved or brought in from a fertile meadow, should be added and graded for the final surface. This soil should be limed if it is acid and fertilized according to need. Generally a rough fertilizer recommendation that applies to many lawns is 25 pounds of a 10-10-10 mixed fertilizer or 50 pounds of 5-10-5 to start; fertilizers having a higher amount of nitrogen may be applied after the grass is established, say 25 pounds of a 10-6-4 to 1,000 square feet. If one is sure that phosphorus and potassium already exist in the soil in adequate supply, a nitrogen fertilizer that becomes available slowly without "burning" the grass is best.

The soil needs to be firm and free of big air pockets, but not hard. Rolling the surface of clayey soils should be avoided because it promotes the formation of hard crusts.

Lawn grasses may be established by sodding the soil surface, by sprigging individual plants or plugs, or by seeding. General recommendations for kinds of grasses to use are given in Department of Agriculture Home and Garden Bulletin No. 51, Better Lawns. Recommendations also can easily be had from your State agricultural experiment station.

Good weed-free sod is both expensive and hard to come by. Weeds in the lawn make a serious problem to many gardeners. It is far easier to keep them out and prevent them from going to seed than it is to eradicate them once they are established in the turf. So the careful gardener prefers sprigs and clean seed over weedy sod.

It is easier to use sod than seed on fairly steep slopes that are to be grassed. When sod is placed on such slopes, many flattish wooden stakes, about 1 to 2 inches wide and 6 inches long, should be driven through it until the tops are just flush with the surface of the sod. These hold the sod from slipping down the slope during wet periods before the grasses become rooted in the soil beneath.

In warm areas, grasses like Bermuda-grass, St. Augustinegrass, and Zoysia can be set as plugs or sprigs or as small sods. Even in the Central States Zoysia is becoming more popular because of its vigorous growth and resistance to drought, heat, and disease, despite the fact that it remains brown during the winter. Plugs of this grass are commonly set out in late spring or midsummer at 1-foot intervals in new lawns. It is well fertilized, watered and weeded while it is getting started. Once the whole soil is well covered, weeds have difficulty establishing themselves.

Lawns in cool areas can be seeded during the spring; but in warm areas early autumn is best so that roots become well established before periods of high heat. Grass seeds are sown most evenly with a machine, but good results can be had with hand broadcasting on a windless day if half is sown in strips laid out one way and the other half in strips laid out across the first ones.

The seed is lightly covered with hand raking and watered lightly with a gentle, fine spray. Only new grass seedings are watered frequently and lightly. Mature lawns should be watered deeply if they are watered at all.

On sloping soils where there is danger of heavy rains before the grass is established, coarsely woven cloth or erosion netting can be staked down over the newly seeded surface to protect it from washing. It is held by small wooden stakes driven down flush with the surface; both stakes and netting will rot away.

After establishing the lawn, if the gardener finds small depressions from soil settling, shallow ones may be filled gradually over a period of years by sifting one-half inch of good garden soil onto the established grass from time to time.

The established lawn needs continual care on most soils. Occasional applications of finely ground limestone may be needed to keep the reaction at about pH 6.5. More than this should not be used. If the soil has been fertilized well with phosphorus and potassium and if -any other deficiencies have been corrected at the start, an annual application of a mixed fertilizer high in nitrogen is commonly used.

Most recommendations suggest an application of something like 20 or 25 pounds per 1,000 square feet, of a 10-6-4 fertilizer in the spring. Unless it is applied carefully when the grass is dry and unless the application is followed by rain or thorough sprinkling, "burning" of the grass is likely. It is much better to split the applications into two or three lighter ones over an interval of some weeks. You can buy a slowly available but high-analysis nitrogen fertilizer that does not burn the grass but gives a slow, continuous supply to the plants throughout the growing season.

In warm, humid areas, however, spring applications of nitrogen often stimulate fungus diseases, especially on clayey soils. Bluegrass, for example, responds readily to nitrogen fertilizer. The plants are luscious and tender. Then during hot, humid days in late May or June, damping-off and brown patch may nearly destroy these susceptible plants. Under such conditions, the main application of fertilizer can be made in early autumn, after the danger of these diseases is past. The grass plants go into the winter with good root reserves and should be given only very light applications of nitrogen during the remainder of the year, except in the shade under the trees, where they should have light to medium applications in spring and summer.

CLOSE CLIPPING with the mower is a common cause of poor lawns, especially in warm places where the hot rays of the sun fall directly on the crowns of the plants. With the mower set high, the clipped plants can stand more heat. A mixture of clover helps to shade the crowns of bluegrass. In cool regions, the grass may be clipped down to 1 inch, but in warm areas 1.5 or 2 inches is better.

Frequently it is wise to leave the clippings on the lawn, because the clippings help to maintain organic matter and nutrients in the surface soil. Heavy clippings from infrequent mowings, however, should be removed to the compost pile and not left as a smothering mat over the grass.