Chapter 8. Composting and Soil Conditioning

The compost pile or heap is the time-honored place for all organic refuse, the real gardener's source of humus for incorporation into the soil. The important thing to remember about composting is that it is a biological process, one that involves bacteria, fungi and other soil organisms. These organisms require food to do their work, which means you must supply the same elements that are needed by higher plants. The one difference is that these organisms do not have chlo­rophyll and are not able to manufacture their own energy foods such as sugars and starches. They draw upon the organic matter for these foods, but in doing so use up large amounts of nitrogen, some phos­phorus and potash and small amounts of other elements. For this reason, the application of fertilizers to the compost pile will allow the organisms to work at their best, provided temperatures are favor­able for their growth and the pile is moist, without being so wet that air is excluded.

Any form of organic matter that will decay can be composted. Some materials, such as peat moss, spent mushroom manure, spent hops and well-rotted manure, are already partially broken down. These can be applied directly to the soil. However, if a substance contains no cellulose, fiber or lignin, it will not produce humus. Dried blood, perhaps the most valuable of organic fertilizers, is all but worthless as a source of humus, since it contains practically no fibrous material. Urine, a valuable source of nitrogen, urea and other fertilizer elements, is another organic substance which produces little or no humus. Fish emulsion fertilizer is another non-fibrous organic material that leaves very little residue for humus formation. This does not mean they are worthless: on the contrary these three materials are among the most valuable foods for the bacteria that work on compost. A little of any one of these will start the pile or get it work­ing again whenever it begins to slow up.

Where and How

The compost heap should be in light shade, on level and well-drained ground. If in full sun, the pile may heat up enough to kill bacteria near the surface. Considerable heat is developed in the com­posting process itself. In dry regions, the pile might well be made in a shallow depression to catch rainfall, but this basin should not be so deep as to risk "drowning" the lower layer of compost.

Unless the soil in the pile site is naturally high in lime, sprinkle the area with ground limestone before applying the first layer. Each successive added layer should also be sprinkled with limestone: the processes of decay generate acids which will slow up bacteria while favoring fungi. If this happens the nitrogen products left behind will be ammonia nitrogen rather than the more desirable nitrate nitrogen forms. The addition of lime favors bacteria rather than fungi.

Build the pile like a giant sandwich of 4-inch alternate layers of organic matter and soil. If your soil is very heavy, it may pay to buy extra "black dirt" for this purpose. While ordinarily I advise against buying outside soil because it almost always is full of weed seed, composting destroys these seeds so they do not become a nuisance.

Between each layer, sprinkle a little chemical fertilizer. Except for fish emulsion, dried blood and urine, organic fertilizers are not desir­able: they, too, must be rotted down before they become useful as fertilizers; thus they add little to the action of the pile at first. The layers can be added one at a time or the entire pile built at once— whichever the available supply of organic matter dictates. As each layer is placed, it should be wet down enough to moisten it thor­oughly but not so much that it is soggy.

Time to Turn

Whether all the layers are laid down at the same time or over a period of several weeks, the entire pile should be turned over and mixed one month after it is completed. The chief benefit of this is to release any excess carbon dioxide that may have accumulated in pre­liminary decomposition, as well as to give bacteria additional oxygen. The pile may have to be wetted down if it looks dry after turning. Turn it over again three or four weeks later. If the pile doesn't seem to be rotting down rapidly, add more fertilizer at this time.

Under ideal conditions—outdoor temperatures in the 70s or above —the compost should be ready to use in about three months. In esti­mating when a particular lot will be done, don't count any month when air temperatures average below 50 degrees. Under such cool conditions the inside of the pile stays warm but the decomposition of the outer layers slows up.

Absolutely any organic substance can be composted (the previous chapter discussed fatty, greasy and oily materials). Dead animals, bones, table wastes, lawn clippings, leaves, weeds, plants pulled from flower and vegetable gardens, hair, wood shaving and sawdust, spoiled grain, clippings from wool goods and many other organic substances are all good raw material for composting.

A Good Start

Special starters or "compost activators," along with weird mix­tures of herbs and other sophistications, are often recommended to "improve" the quality of the finished compost product. These mix­tures include bacterial cultures containing strains that continue working at lower than normal temperatures. They have some value in speeding up decomposition during cool spring or fall weather. Just as effective, however, if available, are bacteria-filled screenings from an old compost pile, well-rotted manure or soil from a rich field. If the only soil available for building a compost pile is a sandy loam, a commercial compost culture will speed breakdown. These should be cultures of bacteria such as Activo, not the herbal mixtures fre­quently mentioned in organic gardening publications.

There is no reason why the pile should have an offensive smell if properly covered with soil: a 4-inch layer of earth absorbs all odors. However, if blood, manures and other rich organic substances be­come a bit odoriferous, add a little extra superphosphate. One cau­tion should be given: do not add large amounts of fresh wood ashes to a compost pile as they form lye and can injure bacteria. Mix fresh ashes with a little damp soil and allow them to stand for a day or two, after which they can be used safely.

ORGANIC MATERIALS WHICH CAN BE COMPOSTED

Dried Leaves: This is the most common material available to home gardeners. It is valuable as a source of humus, but don't take seriously the "richness" of this material often mentioned by unin­formed individuals. Before trees and shrubs drop their leaves in autumn, they withdraw starches, sugars and other food elements from the leaves. Leaves are largely cellulose, so additional starches as well as nitrogen are needed to rot them. Leaves are best if mixed in the compost heap with such materials as stale bread, spoiled flour or meal, and so on.

Table Wastes: Richness of this source depends on how extrav­agant you are. The higher the percentage of meat scraps in table waste, the more valuable it is in compost.

Sawdust: If the master of the house has a home workshop, or if sawdust and shavings are available from a local source, wood wastes make excellent compost. If wanted as a source of humus, use plenty of nitrogen with these wastes, but if you want compost that is less completely converted to humus, add more starchy material and less nitrogen to the pile.

Chicken Manure and Poultry Wastes: Local broiler plants often throw away offal, feathers, etc. Many poultry raisers find chicken manure a nuisance and are glad to give it away; it is sufficiently high in nitrogen but not in phosphorus and potash. These two elements plus starch should be added to speed up chicken waste breakdown.

Brewery Wastes: The spent hops from breweries are about on a par with leaves and require about the same composting attention. One difference: hops are usually wet when received.

Seaweed and Kelp: If you live near the sea, don't scorn the sea's free gift of kelp and seaweed. These are high in potash as well as many minor elements. Additional nitrogen helps speed breakdown.

Nut Shells: Pecan shells, peanut husks, cocoanut fiber and other nut wastes make excellent compost. One precaution: avoid shells of walnuts. They contain a chemical that inhibits plant growth and works like an antiseptic to kill off bacteria.

Tobacco Stems and Wastes: An excellent source of humus and a good soil conditioner when composted.

Fish Wastes: When cleaning fish, always save the offal for the compost pile. Salt-water fish in particular contribute all the minor elements as well as the three major elements in their skin, bones and offal.

Wool Clippings: Worn-out wool clothing should be buried in the compost pile. It will take about two years to decompose. Dark colors rot more slowly than light tones.

Corn Cobs: Although rather high in silica, corn cobs do contain considerable potash and thus are useful in the compost heap. Both nitrogen and phosphorus (at least a sprinkling of the latter) will improve the compost produced by corn cobs.

Sewerage Sludge: If it can be had for the hauling, air-dried sewer­age sludge is worth composting. However, be sure it goes through at least a full year's decay before it is used. Amoeba can survive in sewerage sludge and cause infection in human beings. A full year's composting, if the pile is turned, should eliminate them.

Lawn Clippings: They should be added to the compost heap rather than allowed to lie on the surface of the lawn, where they build up a duff that fosters fungus diseases. Allow the fungi in the compost pile to work on them instead.

Straw, Hay, Cattails: These are low in nitrogen. A compost "food" is needed to rot them. The finished product closely resembles barn­yard manure.

Weeds and Discarded Plants from the Garden: Use these only if not visibly infected with plant diseases. If weeds have formed seed, be sure to place them deep in the pile so the heat of composting will kill the seed.

Tanbark: Not easy to find nowadays, but if available it can be composted with the "food" mixture recommended for straw.

Cotton Nolls and Wastes: Difficult to start a compost with this type of material, but it yields a high percentage of humus. Allow about a year for breakdown.

Paper Scraps: Mentioned here only because paper is often a sub­ject of doubt. Almost pure cellulose, it requires both nitrogen and starches or sugar in order to break down. A small percentage of paper in the compost pile won't hurt. Actually, practically anything of organic origin can be composted in time. I once made some ex­cellent compost with a mixture of straw and some spoiled latex paint, combined with waste blood-albumin gluel.

Applying Organic Matter Directly to Soil

Where space or time does not permit you to operate a compost heap, organic matter can be applied directly to the soil. If this is done in late fall or early spring the organic material should be sprinkled with fertilizer and plowed under. During the growing season this method is impractical. If not offensive in odor, organic matter can be used as a mulch over the soil and worked into the ground after the growing season is over. Here it is important to remember that even though only the lower surface of an organic mulching material is in contact with the soil, rain and sprinkling will wash starches and sugars down from it to the soil organisms which consume nitrogen. Gardeners often are surprised to find their plants turning yellow following the application of a mulch. This can be avoided by the use of a good mixed fertilizer on the soil before the mulching material is applied.

The question is often asked, "How much fertilizer should I apply to compost or to soil on top of compost?" There is no exact formula for this, although a rough rule of thumb is four ounces of actual nitrogen to each bushel of organic matter. This is a much heavier dose than would be applied to garden soil, but it must be remem­bered that there are well over a million bacteria in a teaspoonful of soil and they can use far more plant food than seems possible. Re­member, in the compost pile you are working for maximum efficiency of these soil organisms without depriving plants of nitrogen.

SHEET COMPOSTING

Sometimes a piece of land lies idle for some time, as when property is purchased in anticipation of building a home at a later date. Under these conditions, soil can be built up by what is known as sheet composting, or green manuring. Various plants, such as winter rye (the cereal grain, not rye grass), vetch and buckwheat, are commonly used for this purpose. In the South, lespedeza and kudzu vine are also used.

The green manure cover crop is sown whenever convenient, even in midsummer if artificial irrigation is available. Seed should be sown quite thickly, since the idea is to produce a dense cover to keep down weeds, as well as to grow organic matter to be plowed under. The use of fertilizer in liberal amounts (to a maximum of eight pounds of actual nitrogen to 1,000 square feet) is recommended. This nitrogen will not be wasted, since most of it will be built into plant tissues as protein, which will again be available to lawn grasses or garden plants when the green manure is plowed under and rotted down.

If this process is repeated for a year or two, an amazing amount of organic matter, which finally breaks down into humus, will be added to the soil. Winter rye is particularly useful for this purpose because if sown in fall it will continue to grow every time the soil thaws in winter. After winter rye is plowed under in spring, a crop of buck­wheat or vetch can be seeded, giving a double supply of green matter for sheet composting.

Do not, however, try to squeeze out too much growth the year the property is to be put into lawn or garden areas. If these areas are to be planted in spring, the winter crop of rye should be plowed under at the earliest possible date in late winter or early spring to allow for initial decomposition before seed is sown. If the lawn is to be seeded in August, plowing should be done some time in July. Be sure to apply fertilizer to the cover crop before turning it under, whether this is done in spring or in fall.

Thanks to Synthetics

The roles of lime, marl and ground limestone in flocculating clay and silt have already been mentioned. Synthetic chemical soil condi­tioners, introduced with such a fanfare of publicity in 1952, are dis­appearing from the market. But they should be mentioned because of the contribution they made in calling attention to the need for soil amendment. To no small extent, awareness of this subject may be said to stem from this publicity.

Partly because of their high cost, the products introduced are not likely to come back in their present form. But with the idea once started, who knows what combination of science and commercial enterprise may find a way to make new forms of such materials practical and economical?

Physical Conditioners

Another method of improving soils is to add minerals which in­crease porosity by mechanically opening soils to air and water. One of the oldest materials used for this purpose, a favorite with British gardeners, is ordinary sand. The addition of enough sand to a stiff clay soil should, in theory, separate the particles so that air and moisture can move in freely and thus "correct" the soil so it will crumble readily when squeezed into a ball. Sand should also provide pore spaces in which bacteria and fungi can thrive. This in turn would gradually improve the humus content so that a clay soil would turn into a clay loam. Unfortunately, this end is not always reached when sand is added to clay. Large amounts are needed to bring about any worthwhile improvement. In the final mixture of the two there should be at least one third sand and not more than two thirds clay. If sand is used too sparingly it will, instead of separating the clay particles, merely act like the aggregate in a concrete mixture. The individual grains will be cemented together by the much finer clay particles to form an almost impervious solid. I once saw a stiff clay to which 20 per cent sand had been added; the mixture was so hard it resembled a cement sidewalk. But when another inch layer of sand was spread on top of the soil and worked in with a rotary tiller, the whole mass crumbled and fell apart as if by magic.

For this reason, if sand is to be used to modify clay, say to a depth of 6 inches, at least a 3-inch layer of sand should be spread over the entire area.

This makes sand a somewhat expensive soil conditioner if a sizable area is to be treated.

Other Mechanical Conditioners

One of my favorite low-cost soil amendments is steam cinders. These sharp black particles are the product of burning coal in steam power plants. Because of high temperatures reached in the firebox, individual particles are partially vitrified. They are quite porous, which allows them to absorb a lot of moisture.

They can often be had for hauling. Municipal and private power plants accumulate them much more rapidly than they can be used for construction work, roads, and so forth. I pay about a dollar a yard, which makes steam cinders about the cheapest soil amendment I can buy of any kind.

They are particularly useful in improving lawn soils. They might not be so desirable in a vegetable garden where their harsh, gritty particles would be a nuisance to the gardener working around root crops. I have, however, used fine steam cinders in bulb and per­ennial beds.

The cinders have two drawbacks. One is that they must be pur­chased many months before they are needed. When fresh, they con­tain sulfur impurities which must be leached out before the cinders can be used. I buy them in late summer, pile them behind the garage over winter and use them the following spring. Weathering does a much better job of purifying them than can be done with a hose and water under pressure.

The other defect is that hard, rough clinkers of considerable size are often formed by some coals. This means that the pile must be screened to separate the unusable particles from the fine ones.

Porous Minerals

Two "expanded" minerals—vermiculite and Perlite—have one thing in common—a porous structure which enables them to absorb enormous amounts of water. They are excellent soil conditioners and, unlike either organic matter or chemical conditioners, they remain practically unchanged for years. They are chemically inert and not readily attacked by soil acids or alkaline solutions. While more ex­pensive than most other materials, they have very definite advan­tages. Clean, easy to handle, readily available and, for all practical purposes, sterile when they come out of the bag, they are convenient to use for seed starting or cutting propagation, for house plotting soils and for small garden areas.

If the material is to be visible at the soil surface I prefer vermiculite because it looks more like soil. The white color of Perlite pro­duces a soil mixture that is less natural in appearance. Where the soil is to be used for lawn purposes this surface color factor is unimpor­tant since the Perlite will be hidden by the grass.

Both Perlite and vermiculite can be used in amounts up to one third the total volume of the soil. However, they need not be used as freely as sand. Relatively smaller amounts of either material will bring about noticeable improvement in a soil.

Chapter Digest

A compost pile (two would be better) is the mark of a knowledgeable gardener, for it is an invaluable source of the vital humus that builds Gardener's Loam. Anything organic can be added to a compost heap, and only a very few rules govern its operation. Many common and some uncommon compostable materials are discussed, along with the use of certain "compost starters."

The best soil conditioners are "natural" materials (organic and mineral), whether used on top of or in the ground. They are far superior—in their action and durability—to the overrated synthetic chemical conditioners.

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