A Valuable Resource
Disposing of leaves, grass clippings and other garden refuse is often a problem for households, particularly in urban areas where landfill space is a growing concern. This waste can be turned into useful compost with less effort, energy and cost than it would take to bag and haul it away.
Compost is a dark, crumbly, partially decomposed form of organic matter similar to the organic matter in soil. In many cases the compost will serve the same function as peat moss and thus reduce the cost of gardening. Returning these organic materials to the land maintains natural biological cycles and is an ecologically sensible means of recycling organic wastes.
The organic matter in compost makes heavy, clay soils easier to work by binding the soil particles together. This helps improve aeration, root penetration and water infiltration, and it reduces crusting of the soil surface. Additional organic matter also helps sandy soils retain more water and nutrients.
Although compost contains some nutrients, its greatest benefit is improving soil characteristics. It should be considered a valuable soil amendment, not a fertilizer. In most cases, additional fertilizer will be necessary for optimal growth and production.
Compost is also valuable mulching material to use around garden and landscape plants. Fine compost may be used as a "topdressing" for lawns and, when mixed with soil, a growing medium for houseplants and seedlings. Controlled composting speeds natural break-down of organic waste. Raw organic material is converted into compost by the action of microorganisms (fungi and bacteria). During initial stages of composting, soil microbes increase rapidly. As the materials decompose, certain kinds of microbes dominate. But as they complete a particular function, their activity decreases while others build up and continue the breakdown.
As microbes decompose the organic materials, temperatures within the pile may approach 140 to 160 degrees F at the center. This kills some of the weed seeds and disease-causing organisms in these hot areas. However, in cooler sections of the pile such sterilization does not occur. Turning the pile is therefore important to complete composting and aid in sterilization.
Organisms that are responsible for the breakdown of the organic materials require nitrogen to breakdown the carbon in organic matter. Adding nitrogen fertilizer or materials containing significant amounts of nitrogen is often necessary for rapid, thorough decomposition. This is especially true when using old plant material, dry leaves or sawdust. During the breakdown period, this nitrogen is tied up and not available for plant use. It is released, however, when the composting is complete, and the finished compost is returned to the garden.
What Material May Be Composted?
Most types of yard waste and other organic materials can be used for composting. These include eggshells, sawdust, oak leaves, shredded newspaper, hedge clippings, etc. Some materials, like pine-straw, may be used to a greater advantage as a mulch without composting. Twigs and wood will take a long time to decompose.
It is best not to use diseased plants from the flower or vegetable garden for composting if the compost is to be returned to the garden later. Although some organisms are killed by heating during compost formation, others may escape. Unless the compost has gone through a strong heating, is turned frequently and thoroughly and allowed to remain unused for a year, some of these disease-causing organisms may be returned to the garden with the compost. This is particularly true of bacterial wilt. If diseases have not been a problem, this precaution may not be necessary.
Avoid composting weeds heavily laden with seeds. Even though man seeds are killed during composting, the quantity of seeds is extremely high, they may be returned to the garden with the compost and create extra weed problems.
Most organic kitchen garbage may be used in the compost heap, with the exception of grease, fat, meat scraps and bones. These may attract dogs or other animals and may develop an odor during decomposition. Fats and grease are slow to break down and greatly increase the length of time required before the compost can be used. Further more they are composted commercially.
The Compost Pile
Locate the pile in a convenient, but out of the way, location. Since the compost pile needs to be kept moist, a convenient source of water is helpful. Compost should never get soggy, or the decomposition process will turn septic and create odors. Therefore, don't locate a compost pile where drainage is poor and water may stand.
Try not to locate compost piles close to trees. Tree roots are easily attracted to the loose, moist, organic material developing at the bottom of the pile. During the summer, roots of some trees may spread rapidly throughout the lower areas of the heap, and make the compost dry and difficult to turn. Prune roots at the pile's edge annually if it is near trees, and add water as needed.
The size of pile needed may vary greatly. A pile should not be less than 3 feet wide and 3 feet high. Anything smaller is too small to decompose properly. Large piles work more efficiently, but make the pile comfortable for you to manage. Remember that it should be turned at least once a month.
The average gardener may find that if adequate material is available, two or three small piles provide greater flexibility than a single large one. In this way, a pile may be built and allowed to work, while a second pile serves as a place to put organic materials as they accumulate. Three piles are ideal. One pile is in construction receiving raw material. while a second is developed and composting. A third pile is finishing and ready for use. In this way there is an almost continuous supply of compost.
Containing the Pile
Although it is possible to stack the compost in a loose heap, composting is ideal ,and space is used more efficiently, if it is made in some type of bin or enclosure. Many materials may be used. The sides should be loose enough to provide some air movement through them. One side should open for easy turning and removing of the compost. The pile may be round, square, or other convenient shapes. Special composting bins are commercially available. Many people construct their own. See your county agent if you need blueprints for compost bins.
Woven wire fencing (rat wire, chicken wire), wood slat fencing (snow fence), cement blocks, bricks or scrap lumber can be used to enclose a compost pile. Fencing materials need corner supports, although a small round pile made of slatted fencing needs little or no support. Bricks, or concrete blocks, may be stacked without mortar. Space should be left between blocks to allow adequate air movement through the sides. Scrap boards are suitable for sides if there is enough space left between them for air movement. Lumber is gradually ruined by exposure to the damp compost, and occasionally boards have to be replaced as they decay. Treated lumber may last much longer.
Constructing the Pile
Compost pile construction is often described in terms of layers. In actual practice, such layers are less well defined. Layering is certainly not essential, but it provides the quickest and most complete decomposition. A satisfactory pile can be made by simply blending one part leaves to a few parts of fresh weeds or grass clippings.
Begin the pile layering by spreading an 8-inch layer of organic matter over the base of the pile. If there are different materials available, use the coarsest on the bottom. Shredded or chopped materials decompose fastest. If a lawnmower or shredder is available, coarse organic matter should be run through it. Materials that tend to mat, such as grass clippings, should be placed in thin layers only 2 to 3 inches thick. Moisten, but do not soak, any dry layers as you construct the pile.
Over the layer of plant material, sprinkle ammonium nitrate or a complete, high nitrogen fertilizer such as a lawn food. About ½ cup of fertilizer for each 25 square feet of surface area should be adequate. An equal amount of ground limestone or wood ash can added if pine-straw or woody material is composted. Normally we omit lime to produce a slightly acidic compost that is higher in nitrogen. If fresh livestock or poultry manure is available, a 1- to 2-inch layer may be substituted for the commercial fertilizer. No extra nitrogen is required when composting materials from lush, succulent growth or grass clippings.
Next, add a layer of garden soil about an inch thick. Natural soil contains the microbes that help start the decomposition process. A layer of finished compost may be substituted for the soil. Your plant material is dirty enough to bring some microbes with it, but the soil can speed things along and reduce matting problems. When soil or finished compost and fertilizer are used with layering, special compost activators or starters are not needed for rapid composting. The developed layer just described is the basic unit of construction for a backyard compost pile.
Continue to build layers of organic materials, fertilizer and soil until a maximum height of about 5 feet is achieved. A 3- or 4-foot pile may be more manageable for you. Do not compact it because it is necessary to maintain proper air movement through the pile.
Care of the Pile
The pile must be kept moist (but not soggy) for optimum microbial activity. Excess moisture may cause undesirable decomposition and offensive odors. During dry weather it may be necessary to water when turning. Covering the pile can reduce or prevent moisture loss during extremely dry periods. It can deflect excess rain and avoid a soggy pile.
To speed composting, turn or mix the pile. This will increase aeration of the pile and provide uniform composting. During warm weather the pile should be turned every week or two initially, then monthly. In cool weather, composting is slower and frequent turning is not necessary. During a cold winter, little decomposition occurs except in large pile. The pile should be turned if at any time a strong ammonia or other offensive odor is detected.
Turning may be performed by slicing through the pile and inverting each slice. Where space is available, it may be done by shifting the entire pile into another bin, later to be moved back. The main objective of turning is to shift materials from outer parts of the pile closer to the center where they are better able to heat and decompose. This also loosens the pile to allow for more aerobic conditions. Some composting will still occur without turning.
About two weeks after the pile is started, it should be hot in the center. This indicates the pile is decomposing properly. Failure to produce heat might be caused by too much or too little water, improper aeration, insufficient nitrogen or too small a pile.
As materials compost, the pile should shrink to about half of its original height. The length of time required for composting will vary with the size of pile and the time of year. If the heap fails to work, it may be necessary to restack with some new materials and soil. Remember that the pile is alive and needs proper oxygen and moisture for productive activity.
When compost is ready for use, it should be dark and crumbly, with much of the original identity of the materials lost. Finished compost should have an "earthy" smell. If compost becomes old, it still makes a good soil amendment, but much of the nitrogen will be lost through volatilization or leaching. For this reason, use compost as soon as possible after it is finished. If fresh compost is blended into the soil, less nitrogen will be lost to volatilization. Use between 6 and 18 pounds of compost per square yard of garden area to maintain or improve your soil.
Normally, compost will be ready for use in two to nine months, depending on the types of organic materials used, the environmental conditions and maintenance. For many purposes, the finished compost is easier to use if it is first screened through a 1-inch wire mesh to eliminate coarse or incompletely decomposed materials.
Compost can be used for potting houseplants or for starting many seeds. Since thorough sterilization is important for some uses, especially for starting seeds, the compost may be pasteurized (sterilized) before use. Length of time for sterilization varies with volume. Place the moist compost or soil mix in an oven preheated to about 200 degrees F, and heat until the center of the mass reaches a temperature of about 160 degrees F. Maintain that temperature for 30 minutes. A probe-type thermometer (meat or candy) may be helpful for determining whether the center has been properly heated. Excess heating is not necessary and can be harmful. Maintain good ventilation to remove odors. Be sure to remove the soil as soon as it has been sterilized, and allow it to cool before using.