Chapter 12. A Little Digging Goes a Long Way

How unfortunate that the term "in good tilth" is passing out of common use! Today it is seldom used to describe a state of well-being in soil—a "oneness" of mellow loam and the gardener's care lavished upon it.

In its place we now use more specific terms which accurately but unpoetically describe some fraction of soil condition—texture, struc­ture, aeration and permeability.

Land in good tilth is well drained, yet holds its moisture tena­ciously against the ravages of drought. Water seldom stands on the surface of Gardener's Loam for more than a minute or two before seeping deep into the intricate maze of passages between crumbs of clay, silt and organic matter. When such soil is dug or plowed the clods do not hang together in hard lumps but crumble to a loose, amorphous mold. Such a soil is rich in natural fertility—stored nutrients adsorbed on the clay and loam particles, as well as more tightly held in the humus that is so vital to good tilth.

One of the true delights of spring is the smell of such a soil being prepared for planting. As it is stirred by plow, tiller or spade, it emits a special fragrance which to a true gardener is the essence of the most wonderful time of the year—the awakening of living things to a new season of being. If you were to say that this fragrance re­minds you of violets, you would be right, since the "top note" of aroma given off by damp earth contains at least two compounds also found in violet perfume.

Contrast a soil in good tilth with one in poor condition. The latter is hard to work. An old English phrase for poor soil is particularly expressive; it is called "four horse land," meaning that four horses are needed on the plow to turn the ground over in spring. When wet with winter snow and rain, such soil can be cut into slices like a pasty process-cheese, and it turns into hard ridges instead of crum­bling. When four horse soil is dry, deep cracks furrow the surface and tillage tools can hardly break through. Unless worked at exactly the right time, it packs to brick-like hardness.

What Contributes to Good Tilth

Good tilth is the product of many things. Perhaps the most impor­tant (except in muck-peat soils) is the use of generous amounts of organic matter. Another, described in the chapter on pH, is the lime-flocculation of clay particles which opens soil passages that allow the free movement of air and moisture. Proper provisions for drainage and aeration are also part of the complex of good tilth.

Even though all other provisions are made for improving the con­dition of soil, all can be undone if the soil is worked at the wrong time. Most garden soils (not sandy types, however) can be griev­ously compacted by just one cultivation if the job is done before the excess moisture of spring has drained away. Often it takes an entire season to bring the damaged soil back into a "good tilth" condition. For this reason you must learn to recognize the stage at which excess moisture has passed off so the soil can be dug or plowed without danger of compaction.

The Mud Pie Test

A quick, simple way to see the moisture condition of your soil is the mud pie test. Pick up a handful from the surface, selecting a spot that is neither wetter nor drier than the rest. Squeeze this soil between the hands and try to form it into a ball. If the soil is too wet, water may ooze out. Even if this does not happen the soil may still be too wet to work safely if it packs into a solid ball. Another "stop sign" is if the soil breaks into large, hard lumps. If, however, the soil is in condition to work you will not be able to press it into a dense ball. It will be loose and will crumble freely in your hands or when dropped.

Some soils, particularly those that contain too much clay, can become too dry. In such cases, a ball will not form when soil is pressed between the hands. The length of time it takes a normal soil to pass from the too-wet to the just-right stage is a rough measure of the quality of that soil.

Soil Amendment

Few homes are chosen primarily because they are on land where the soil is in good tilth. Often the owner does not know what kind of soil he has until months after he has moved in. In nine cases out of ten, it can stand improvement.

Most development (speculative) housing is on property from which all topsoil is stripped before building work begins. The thin layer replaced after each house is completed serves no purpose other than to camouflage the fact that the owner will have nothing to work with but subsoil. What is needed in such situations is soil condition­ing. I hesitate to use that term because it has acquired a significance in the past few years which I do not wish to give it. Millions of Americans were made conscious of "soil conditioning" for the first time about 1952 when the chemical Krilium was introduced.

Although I want to give modern science its full due, I should like to point out that soil conditioning is as old as agriculture itself. Any­one who feels that soil may only be modified by the addition of cer­tain modern chemicals will do well to refer to the works of such ancient Greek and Roman writers as Columella, Pliny and Aristotle. They knew nothing about chemical soil conditioning, of course, but they were familiar with the effects of treatment. They recommended lime and marl to loosen soil, as well as organic matter of both animal and plant origin.

Positive and Negative

Basically, the effect of all such substances, as well as modern chemical conditioners, is to supply positively charged particles which attract the negatively charged clay particles. When these combine they form clumps or floccules. The chemistry of this process is quite complex, involving both organic and inorganic colloids. Rather than attempt to go into every possible combination and how to treat it, let us return to our Chapter Two discussion of pH. By maintaining the pH of a soil between 6.0 and 6.9 (whether we add lime to a too-acid soil or sulfur to one that is too alkaline), we can solve most of the problems involved. The one major exception is in the case of soils where sodium colloids predominate—for example the drylands area of the Great Plains—but the addition of gypsum to such soils will convert the alkali carbonates into sulfates, reducing the harmful effects of sodium salts.

Wherever heavy clay exists, the most economical and effective way to condition soil is to add organic matter. Pound for pound it is not nearly so effective as modern chemicals, but dollar for dollar the cost is about one tenth that of chemical amendment. Where pH is so low that lime is needed, the use of ground limestone should also be a part of the conditioning. Organic matter, however, has advantages possessed neither by lime nor modern chemicals. (See related dis­cussions in Chapter Eight.)

Organic matter improves tilth in every way. It provides a steady supply of fertility by the constant breaking down of plant and an­imal wastes, releasing the food elements they contain. Reduced to a more stable form—humus—it has been known to continue feeding for as long as half a century after application. Its spongelike struc­ture blots up excess moisture and stores it against periods of drought. It forms crumbs with clay that open up passages in too-tight soils. Without generous supplies of organic matter, bacteria and fungi cannot thrive but when it is present they contribute their functions to good tilth.

Physical Conditioning

Any working of a (not-too-wet) soil tends to condition it by loosening it for deep root penetration, incorporating air and blend­ing any surface organic matter into the lower layers. From the crooked stick of primitive man to the modern rotary tiller is a long, long way, yet both these implements had a common purpose—to condition soil and make it a better place for plants.

Except for tillage to kill weeds, the other benefits obtained from working the soil belong under the heading of soil conditioning. All these benefits result, of course, only when the gardener digs or plows at the proper time, as determined by the mud pie test, or by the experienced eye.

TRENCHING

Perhaps the ultimate in soil preparation and conditioning is the operation our British cousins call trenching. Trenching is sometimes confused with double digging, a somewhat less exacting and labo­rious operation. Trenching is an elaborate procedure during which the soil in the entire garden area is completely inverted, with the lower layer on top and the topsoil buried at least six inches beneath the surface. Underneath this "upside-down cake" the underlying subsoil is worked to an additional depth of several inches.

The operation begins with a trench dug to the depth of a standard garden spade entirely across one end of the garden (or lawn) area. The soil from this trench is wheeled to the far end of the area, where the work is to finish. Next the soil from the layer below the surface in the first trench, which may include some of the subsoil, is also dug out to another spade's depth and wheeled to form a pile alongside first. This leaves a trench, two spades deep, along one edge of the intended lawn or garden area.

Into the bottom of this trench a layer of organic matter is dumped and spread to a depth of two or three inches. Fertilizer is then sprin­kled over this to help decompose the mass.

Because of the depth of this trench, it makes an excellent place to dispose of any weeds or other vegetable trash that may be around. Even if weed seeds germinate there is no chance that they will sur­vive to reach the surface. The only thing to avoid are plants like Canada thistle and bindweed that have deep perennial roots which can grow through many inches of soil. Either fresh or composted organic matter can be used.

If the trenching is done in fall, it offers a good way to dispose of fallen leaves. Too, working during cool fall weather is much more pleasant than during the warm days of late spring and summer.

Deep Down

Now dig in the organic matter in the trench bottom to the depth of a spade, mixing it well into the subsoil. If this is heavy clay, some ground limestone can be added to help loosen it. Any modification of pH should be made at this time: you will not have another chance at the subsoil for a long, long time. One job of trenching should last at least ten years.

If the soil is poorly drained, the time to make corrections is when the trench is open. To lay a drainage tile line, begin digging at the lowest point of the garden and lay the tile away from this trench to a lower spot so water that accumulates in the loosened soil has some place to go.

The next step is to dig a second trench alongside the first. The topsoil from the second trench goes in the bottom of the first, cover­ing the organic matter. Next the lower layer from the second trench is placed on top of the topsoil in the first trench.

This operation, repeated across the garden, works the soil to a depth of three spades, or approximately 18 to 20 inches deep. It places rich soil and organic matter down deep, where the roots of plants can reach them. For a year or two, fertilizer applications to the area should be doubled, to make up for the decreased richness of the subsoil that is now the topsoil layer. Soon, however, as plant residues and roots are worked into this surface soil it improves in richness and tilth. If your subsoil is very poor, improve it before shoveling it into the preceding trench.

Not Always Advisable

Obviously, trenching is not always worth the time and effort in­volved. It would be completely wasted, for example, if only shallow-rooted crops such as petunias and lettuce were to be grown. In rich, deep, black prairie soils such as are found in parts of the Middle West, topsoil may extend down two or three feet, so that the soil dug out of the bottom of the trench would be just as rich as the top.

Certainly, trenching is not an operation for an older gardener or a man with a poor heart. It is hard work, and not to be undertaken lightly. However, rewards are high when the operation is needed and properly done. For example, it is ideal when a hedge is to be planted, in which case only two trenches need be dug.

Double Digging

The labor involved in true trenching has led to the development of a substitute operation called double digging. Here only a single-depth trench is opened and the earth wheeled to the finish line. Organic matter is worked into the bottom of the single-depth trench and topsoil from the second trench applied over this. Except for the wheeling of the soil from the first trench to the finish line, double digging actually requires no more physical effort than ordinary dig­ging; in both methods, every clod should be turned completely over. With either trenching or double-digging, there is little tendency to develop a hardpan or "plowsole" deep in the soil because when the ground is worked in succeeding years, the spade or tiller will not penetrate to the depth previously reached.

MECHANICAL TILLAGE

Despite the saving in effort made possible by power-driven tillage equipment, I still like to dig by hand. There is something about this task which lifts it out of the class of drudgery, even though in turn­ing over a thousand square feet of garden I may move several tons of soil. The smell of earth in good tilth, the sun and wind and the feeling of kinship with the world of plant life just cannot be dupli­cated by the chugging of a garden tractor.

Unfortunately, limitations of time and physical strength will not always permit us to use our muscles for soil preparation. With just so many hours in a weekend, we cannot afford to do a little at a time. Before we could finish the job the best time for seeding and planting would be past.

The gardener is, therefore, faced with the problem of selecting the most satisfactory form of tillage machinery, whether he buys it out­right or hires his work done. Most present-day garden "plowing" is done by rotary tillers. These work on the principle of a revolving shaft to which are attached sharp tines that penetrate the soil as they make a complete revolution around the shaft. The tines tear out roots, trash and plant wastes, chewing them into small pieces and burying them in a loose, fluffy duff of soil. Any organic matter, fertilizer or soil conditioning material applied to the surface is thor­oughly and uniformly mixed in.

Small home-sized power tiller units are available but are usually too low in power to do a good job of deep tilling. Six inches is about the maximum depth you should expect from these small units. Actually this is deep enough to loosen the soil for the roots of most garden plants, but not where large amounts of organic matter are to be incorporated. About eight inches is maximum for most larger units. Both sizes are adjustable so they can cultivate from a fraction of an inch in depth, down to their maximum depth.

Although great labor savers, rotary tillers are not ideal. One ob­jection to the type with sharp tines is that it produces too fine a soil particle. Excessive tilling with this type of equipment breaks down the structure of the soil and brings on heavy crusting. Many home gardeners are disappointed when they find that the loose, fluffy loam of spring has turned to a crusted solid mass by midsummer, into which water penetrates with difficulty. Another result of too-fine a particle is that more organic matter is needed to improve tilth fol­lowing the use of a tiller. Apparently many of the organic particles get coated with clay so thoroughly they cannot act as soil condi­tioners. Most modern machines now have a cutting-knife tine, set at an angle, which does not churn the soil to a fine dust.

Another drawback of rotary tillers is their tendency to build up a tillage pan—a hard, water-tight layer just below the loosened soil. I have taken a spade and removed the loose layer of soil right after tilling and found beneath it a layer of packed soil almost too firm to show a heel print.

The tendency to crust and pack can be overcome by supplying the soil with extra organic matter or by using a mechanical soil condi­tioner such as leached steam cinders, vermiculite or Perlite. Sand is not a good material to use: its aggregate-in-concrete effect is ac­centuated when in contact with fine clay particles. I estimate that between 33 and SO per cent more organic material is needed in a soil when a rotary tiller is used than when the same soil is plowed or hand-dug. Of course, when this extra material is supplied, the result is a rich, deep, mellow loam in perfect tilth.

The problem of a tillage pan is not quite as easy to solve. The ideal answer is to trench the entire area before a tiller is used, after which a pan may not build up for many years. The compacting effect can be delayed somewhat by changing the depth to which the tines penetrate each time the soil is worked. In farm practice, chisel plows are used to drive a sharp narrow point through the tillage pan and shatter it. To my knowledge, there is no available home garden ver­sion of the chisel plow. Some smart manufacturer of rotary tillers would do the gardening fraternity a favor if he would develop such a device that could be interchanged with the tines for use at least once a year. It would bring rotary tillage close to perfection.

Mouldboard Plows

I have always been thankful that I was born near open fields. Although our home was in a city of over 2,000,000 population, we were surrounded by farm land on three sides and each spring could watch sturdy brown teams pulling old-fashioned mouldboard plows through the rich prairie loam of our area.

The action of a mouldboard plow is nothing short of poetry in motion. It is not a simple knifelike edge, slicing its way through the soil. Instead, the furrow slice is cut loose by the sharp edge and shin of the plowshare and forced against the plow surface. It strikes at such an angle that it is at first crumbled and granulated, and then turned, inverting the soil and depositing it on top of trash and plant residues. If the physical condition of the earth is good, no other device can do a better job of granulation and covering.

Old Dobbin's hoofs were not very large and did not compact the soil to any extent. The same cannot be said for many tractors which are heavy enough to cause serious compaction. Some of the smaller riding tractors, which weigh less than a horse, are a good com­promise. Their one weakness is that they often lack adequate power, but if used at a fairly slow rate and with not too large a plowing attachment, they do an excellent job.

Chapter Digest

Gardener's Loam and "good soil tilth" are synonymous. Achieving such mellow soil almost always requires some tillage. After testing (perhaps by the mud pie test) to determine whether the soil's moisture content is favorable, the gardener can use a manual or mechanical method to prepare the ground for planting. Trenching, double-digging, and rotary tilling are effective methods—and if carried out properly they need not involve burdensome labor.

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