Your Lawn’s Underpinning: Grades And Grading For Drainage

While you are thinking about the various elements of lawn-making (rehabilitating the established lawn is covered later), ask yourself this question: "If I were to upset a 100-gallon barrel of water in the middle of the area where I want to plant a lawn, where would the water go?" The answer is of vital importance.

If the soil is friable loam (the best for lawn purposes) most of the water will soak in within a few minutes. Some will pass downward into the soil's natural sub-surface drainage channels; a little of it will flow outward along the surface but will be gone long before it reaches the edge of the lawn. A small amount may pass off by evaporation, but so little as to make no difference. Much of it will be blotted up by spongy elements in the soil and held for use by the grass.

In a very sandy soil the water also disappears quickly, but instead of being soaked up or trapped underground, much of it will pass off before the grass roots can absorb it.

On a heavy clay soil, particularly if the surface is level, the water may remain on top for a long time, often until it disappears by evaporation. If the surface slopes, the water may run off without penetrating. If the soil is heavy in clay but contains some organic matter, a portion of the water will gradually soak in but so slowly that a substantial part of it will be lost through evaporation.

Thus, in the disappearance of 100 gallons of water under various conditions, we can see the reason why the first important step in lawn-making is site analysis to determine the grade of the land and related factors. Part of this "site analysis" considers the soil so important a subject that it is reserved for separate discussion in the next chapter. Part of the study concerns the slope of the land—the natural path of runoff water from rains too heavy for the soil to blot up at once. First attention, however, is given to a phase of lawn-making which ninety-five out of a hundred homeowners never consider at all—underground drainage.

All too often, the lawn-maker takes drainage for granted—if he thinks about it at all. Here is a good place to emphasize the old adage, "Make haste slowly." Even if assuring proper grade and drainage means that you must lose a season or a full year in establishing a permanent lawn, it still will pay you to do the work right. Recently I had a chance to examine a plot of turf I seeded half a century ago when I was a boy in grammar school. Because this lawn happened to be planted on a rich sandy loam that presented no drainage problem, it thrived in spite of my lack of experience. After fifty years, the original grass is still in good condition, due to proper care. Keep in mind that the lawn you are making may still be in existence a hundred years from now—and that is not a long life for healthy turf. Don't be tempted to rush through without preparing both site and soil in a careful manner.

The Mud-Pie Test

The one time when you must not do any digging or grading, regardless of the need for haste, is when the soil is wet. This is a standard precaution observed almost automatically by the man who has a vegetable garden or flower border, but lawn-makers all too often ignore it, thinking a lawn's soil does not need this care. Almost the opposite is true, for the roots of grass plants are much more sensitive to compaction than those of most plants. Thus, working the soil when it is wet comes close to being a horticultural crime. The soil will lose its air spaces and may even be hammered into rocklike hardness that will curse the lawn throughout its life.

Everyone who works with soil should know the mud-pie test. It is usually thought of in spring, but it can be applied at any time. Pick up a handful of soil and squeeze it between your palms until it forms a ball or pie. Now crumble it between your fingers. If it breaks up easily and does not hold a ball form, the soil is in good condition to work. If it clings to its original shape, the soil is too wet and you should wait until it dries out before working it in any way.

Sometimes disadvantages may be combined and turned into assets, as in the case of the too-wet lawn soil that requires the addition of peat moss. As a rule, before peat moss can be mixed with soil, it must be wet down until it breaks up easily, a tiresome chore. This preliminary soaking is necessary because dry peat moss tends to pull moisture out of the surrounding soil. So, we take the two problems—dry, moisture-hungry peat moss and overly wet soil— combine them, and Presto—two problems solved. Merely spread a layer of dry peat moss on the soil and it will blot up gallons of excess moisture.

Slight Slope Best

For some reason, an absolutely level lawn is the ideal of many Americans. That is one tradition we did not inherit from the British, for in England's damp climate a lawn's success almost invariably depends on perfect drainage. A gently-rolling area for a lawn is valued. Our home-builders, however, turn out a property on which a drop of water has no place to run. On light sandy loams, where water disappears very rapidly, a level lawn is advantageous. Otherwise, a perfectly level surface should never be allowed to exist. Drainage problems on such a lawn are almost unavoidable.

At the same time, I fully realize that many, if not most of us, have little or no choice or voice in the grading of our properties, and none at all concerning neighboring land. So we must work with the front, back and side yards we already have. We take the site and make the best of it—soil and topography alike. Few homeowners have facilities for moving large amounts of earth to alter substantially the grade of a lawn.

Nevertheless, each one, to the best of his ability, must work for a beautiful lawn. To this end, the ideal slope is between one-eighth inch and one-quarter inch to the foot. In other words, four feet or eight feet out from the foundation, in any direction, the lawn should be one inch lower than at the house line. This slope should continue at the same rate all the way to the property line. The closer we can come to meeting the ideal, the less trouble drainage will be. The one-quarter inch rate of slope is about maximum. If the grade is made steeper, some washing may occur in heavy rains. One-eighth is about minimum for the slope; if less, surface water may not run off freely.

A Work Estimate

How much work is entailed? Well, if your house stands forty feet from the sidewalk, for example, and you want a slope of one-eighth inch, you will, in effect, have to add about five inches of soil at the house and remove five inches at the sidewalk line. Actually, of course, the change in land height will be gradual. To minimize the soil-hauling labor, the necessary cutting and filling should be done from both ends toward the middle, or vice versa, rather than all at the house or all at the walk.

On a completely new lawn, such as one surrounding a newly built home, this cutting and filling should be done on the subsoil, if at all possible. The building contractor's grading equipment will make short work of the job. If you have to do it by hand, and the area has been packed hard, first loosen the earth with a rotary tiller. If the builder has put "topsoil" in place, it probably is not only of questionable quality but is no more than a two-inch layer, of very little value. Also, the subsoil will have been compacted. In such cases, rather than trying to save the "topsoil," you would be wise to simply ignore it and work over the entire area with the rotary tiller. Set the tines to plow eight inches deep. This extra tilling work, loosening the soil, will greatly ease your manual grading labor. Of course, if the contractor has used good "topsoil," four to six inches deep, it should be removed and piled to one side before you work on the subsoil.

Sometimes giving the land a slope will be inadequate to assure good drainage. This occurs most often in very heavy soil, or where an impervious layer of clay (called hardpan) is located a few feet below the soil surface. To find out what you are up against, dig a "soil profile" hole. Dig it two feet deep and large enough so you can see into it. Cut the sides straight, so the different layers of soil will be clearly visible.

The upper few inches will usually be very much darker than the lower layers. This darker crust, the true topsoil, will be discussed in detail in the next chapter. At the moment we are interested in the subsoil, the neglected foundation of every lawn. This differs from the topsoil in being practically lifeless. It is almost devoid of organic matter (essential to bacteria), and is usually low in fertility.

But in this chapter we are interested in the subsoil's ability to carry away excess water from the lawn. If it is sandy or full of stones or coarse gravel, probably nothing needs to be done to improve drainage. If it is a stiff clay, the chances are that it is not a good outlet for surplus water during periods of heavy rainfall.

Drainage Tile

When there is any doubt of the subsoil's capacity to handle runoff, you should lay drainage tile under the whole lawn. Lines of drainage tile should fall from one-eighth inch to one-quarter inch to the foot. About three feet in from the upper edge of the lawn, dig trenches thirty inches deep about six feet apart. These should all lead to the lower part of the lawn. It is important to provide an outlet which will take the water from this low point and drain it off. If this is not done and the tile has no outlet, it will merely fill with water and the soil will be just as wet as before.

This is a job which must not be skimped. Be sure there are no pockets in the lines of tile to trap water. The tiles must fall evenly to a low point. After laying, cover the lines with tar paper and then cover this with sand. The tar paper and sand prevent fine soil from silting down into the lines and clogging them. The tiles are, of course, laid with open joints so the water in the soil can enter them freely.

If you are long on lawn area and short of time or energy, have the tiling done by a professional. But if tiling seems too arduous a job or too expensive and the area is really low, a mixture high in bent grasses is advisable. The bents have a thirst for moisture and are more likely to succeed in soil that is constantly damp than are fescues or bluegrasses.

After the subsoil has been filled back over the tile, the area is ready for rough grading. But first take time to mix some form of humus or other organic matter into the subsoil. Many modern grass varieties owe their superiority to their vigorous roots, which can forage deeply into the subsoil for moisture and nourishment. The addition of peat moss, spent mushroom manure, leafmold, well-rotted compost or sawdust will give these roots something to feed on for years.

Sawdust Foundation

If sawdust is used, add a cupful of sulfate of ammonia to each bushel. This is necessary because soil bacteria use up large amounts of nitrogen as they break down the sawdust. If extra nitrogen is not supplied, the bacteria may cause a nitrogen deficiency in the soil.

The best lawn I ever made was based on 3 inches of sawdust (supplemented with sulfate of ammonia), worked into the subsoil six inches deep. Two inches of topsoil over this base gave me a perfect lawn soil for establishing a thick, heavy sod that for four years has never had one drop of artificial irrigation.

Another way to improve the subsoil (but this adds no plant food) is to incorporate sifted cinders that have been allowed to weather over winter before use. These should be sifted through 3/8-inch mesh to get rid of any large lumps. On a heavy clay subsoil, working in a 3-inch layer of sifted cinders will make a remarkable difference in drainage. Be sure they are really worked in and thoroughly mixed with the soil.

In areas where soils are strongly or even moderately acid, limestone screenings—the fine chips used as a top dressing on driveways —make an excellent subsoil amendment. They can be used on both the subsoil and on the surface. Lime does not make the soil too alkaline until there are fewer than eight clay particles to one of lime (see the discussion on soil pH in Chapter 5).

A word of caution about the use of sand as a soil amendment: Sand is often recommended by garden writers, most of whom probably live where loam soils are prevalent and clay is not a problem. The difficulty is that enough sand to turn heavy clay into a fine, mellow soil would cost a fortune for a sizable lawn. At least one-third as much sand as clay must be in the finished mixture, otherwise the effect of the sand is to act like the aggregate in concrete, with the clay particles acting as the cement. If too little sand is used, the soil will be harder than before.

The cost of sand can be high. In most big cities, washed sand, the only kind available, runs about $5.00 a yard delivered. A heavy clay area, 20 by 50 feet, for example, would require 10 yards of sand.

Final Grade

After you have laid drainage tile, modified the subsoil and otherwise adjusted the underlayers of soil, you may find that regrading is needed. This is usually the case even if the original grade was established with care. For the job, you will not require expensive grading and leveling machines unless your lawn covers several acres. I find that one section of an ordinary extension ladder, from 10 to 20 feet long, will do two grading jobs almost as well as the special devices used by professionals. Lay the ladder along a slope, and set a carpenter's level on one of the side rails; this will indicate how the soil surface runs. Variations from the desired grade can be marked with a stake driven to the depth of the bottom of this side rail. The stake will show how much soil must be added to bring the area up to level.

The ladder also serves as a drag grader, doing as good a job as a fancy land plow or plane of the type used for leveling irrigation projects in the West. The ladder works on the same principle, incidentally. A strong rope is tied to each end of one side rail, forming a handle by which the ladder can be dragged sideways across the soil surface. As the side rail meets soft dirt, it pushes this in front of it. When a hole is reached, enough of the soft dirt is deposited to fill it. Any remaining soil, plus soil from other high spots, is caught by the other side rail and carried along until another hole is reached.

Several passes over the surface with such a grader will leave a soil surface that only needs a little hand raking to meet every requirement. In heavier soils, the ladder may bounce around without cutting. If this happens, lay a plank across the rungs and weight it down with a concrete block or two.

With the completion of all these preparations, your lawn-to-be is ready for topsoil.

Chips Off The Chapter

1. Make the theoretical "water-barrel test"—it will reveal some interesting things about the grade of your lawn. The mud-pie test will tell you when the soil is too wet to handle.
2. A proper subsoil and surface grade—sloping slightly away from the house—should be your first order of business. A poor job will be a permanent handicap to your lawn.
3. Drainage tile may be needed.
4. Improve the subsoil with organic matter, cinders, etc. In fact, you can gradually build up the poorest subsoil into a fine grade of topsoil.

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