Composting Methods

Introduction

The secret to successful composting is to select an approach and technique that suits your needs and lifestyle. Your choice will depend on a number of factors such as how much space you have available, what materials you have, how you plan to use the compost, how much time you want to spend, and how neat you want your compost pile to look. For example, if you only need a little compost, want to expend minimal effort, and have a small area to do it in, your best choice might be a commercially available bin. If you have plenty of space and want large quantities of compost quickly, you may want to build a deluxe three bin unit. If you want to compost vegetative food waste separately, you may find it easiest to directly incorporate them into the soil. This lesson will cover four methods of composting: holding units, turning units, heaps and sheet composting. Other composting alternatives such as leaving grass clippings on the lawn, mulching, and vermi-composting (worm composting) are discussed later.

Holding Units

Holding units are bins used to hold yard and kitchen materials until composting is complete. They need relatively little maintenance, and some models can be used by apartment dwellers for composting on balconies. Nonwoody materials can be added to a holding unit as they are generated. (Many of the commercial one bin systems sold in stores and mail-order catalogs are holding units.) Using a holding unit is one of the easiest ways to compost but is generally slower. This type of enclosure makes it difficult to turn the heap as a way of increasing oxygen. No turning is required, but the lack of aeration causes the composting process to take from six months to two years.

The process can be hastened by using portable bins. Some lightweight units are designed to be taken apart and easily moved. These units can be removed from an existing heap and transferred to an adjacent location. The heap is then turned back over into the unit, mixing and aerating materials. Portable units can be purchased (usually plastic) or constructed from circles of wire fencing or hardware cloth, snow fencing, or wire framed in wood.

Other folks attempt to improve aeration in holding units by adding one or more ventilating stacks or by poking holes into the pile. Ventilating stacks need to be placed into the center of the bin prior to making a pile. Stacks can be made out of perforated pipe, a cylinder of wire mesh or even a bunch of twigs loosely tied together. PVC pipes should be at least one inch in diameter with holes drilled randomly along the length. They can be inserted vertically or horizontally. Another alternative to improve aeration is to place the holding unit on a wood pallet or plastic aeration mat (available from composting equipment dealers).

In holding units, stages of decomposition will vary from the top to the bottom of the heap since yard trimmings and other organics are added continuously. Typically, the more finished compost will be found near the bottom of a pile. Finished compost at the bottom can be removed and used. How easily one gets to the finished compost depends on the type of bin used. Some holding units are designed with a removable front or small doors at the bottom of the bin. With portable bins, finished and unfinished compost can be separated using a similar method to the one described previously. The portable bin should be removed and set nearby. Less decomposed materials from the top of the pile can be put into the empty unit until finished compost is uncovered. More effort is required for heavy or permanent holding units without removable doors. Unfinished compost must be removed and placed in an adjoining unit or temporary storage container. If you have room, it is helpful to have two or three stationary units. One bin can be used for fresh organics, another for maturing materials, and possibly, a third for finished compost.

In addition to the portable bins mentioned earlier, there are numerous other types of commercial and home-built units. Stores and mail order catalogs typically sell units made from plastic and occasionally wood. Home-built units can be constructed from pallets, lumber, hardware cloth, tires, and metal barrels, among other materials. Some people like the appearance of permanent structures which can be made from landscape timbers, concrete blocks, rocks, or bricks.

If you plan to build a wood composting unit, avoid using this lumber treated with copper arsenate (CCA), creosote, and penta. (You should also avoid using the lumber around vegetable gardens.) Toxic compounds from the wood preservatives could leach into your compost. The compounds are harmful to humans and pets. They have been shown to cause cancer and skin and eye irritations. Use wood that is naturally resistant to decay such as cedar or untreated pine. Structures built from pine will probably have to be replaced within a few years. By then, you may be ready for a multiple bin unit or a new design.

Turning Units

Turning units are systems designed to be turned or aerated. These units work faster than holding units, because aerobic bacteria are provided with the oxygen they need to break down materials. There are two general forms of turning units: either a series of bins, or a rotating barrel or rolling ball. When organic materials are turned and mixed on a regular basis (every five to ten days), compost can be made in two months or less (assuming a good carbon/nitrogen mix and proper moisture content). Frequent turning offers important advantages in addition to faster composting. Higher temperatures produced as a result of turning (90° - 140° F) will kill major disease organisms and fly larvae, help kill weed seeds, and provide a good environment for the most effective decomposer organisms.

Turning systems typically cost more than holding units and/or require greater effort to build. Turning composting materials in multiple bins and rolling balls may be difficult for people with back problems or limited physical strength. In contrast, some barrel units are designed for ease of turning and maintenance. These systems may actually be easier to use than holding units for older or physically challenged composters. Barrel units tend to have smaller capacities than most other bins, which make them better suited for people with small amounts of yard trimmings and food scraps.

Materials need to be carefully prepared and added to turning units in stockpiled batches. Materials should be saved until there is enough to fill one bin of a multiple unit, or to fill a barrel unit to the prescribed level. Food wastes can be accumulated in a pest-proof container such as a plastic, five gallon bucket. If necessary, sawdust can be added to the top of each day's scraps to reduce odor.

Heaps

Heap composting is similar to composting with holding and turning units except that it does not require a structure. Recommended dimensions for a heap are 5 feet wide by 3 feet high. Length can vary depending on the amount of materials used. Heaps take more space due to gravity. The wider width will help the pile retain heat better. Materials can be added as they are generated or they can be stored until enough are available to make a good sized heap. During fall months, making a good sized heap will help the composting process work longer into the winter season. Ideally, two heaps are better than one. When the first heap is large enough, it should be allowed to compost undisturbed. A second heap can be started with new materials.

Turning a heap is optional. The composting process will obviously take longer if the pile is not turned. Food scraps should not be thrown on an unturned pile because pests are likely to be attracted. Woody materials may also pose a problem. If woody materials are not cut up into small pieces, the pile may tend to become more of a brush pile than a composting pile. A woody pile decomposes extremely slowly, usually over a period of several years, and can become huge quickly.

Sheet Composting

Sheet composting is a way to obtain the benefits of decayed organic material without building a composting pile. Sheet composting involves spreading a thin layer of organic materials, such as leaves, over a garden area. The materials are then tilled in with a hoe, spade, garden fork, or rotary tiller. Leaves, garden debris, weeds, grass clippings, and vegetative food scraps are examples of materials that can be easily tilled into the soil. To aid decomposition, materials should be shredded or chopped prior to layering.

The danger of sheet composting as a compost-making method is that carbon containing residues will call upon the nitrogen reserves of the soil for their decomposition. On the other hand, high-nitrogen materials may release their nitrogen too quickly in the wrong form. What may take a matter of weeks in a compost pile, given confined and thermophilic conditions, may take a full season in the soil.

To ensure adequate decomposition of organic materials before planting, it is best to do sheet composting in the fall. Spread a 2 to 4-inch layer of organic materials on the soil surface and till in. A rotary tiller will do the most thorough job of working materials into a vegetable garden. In a flower bed containing perennials and bulbs, it may be necessary to carefully work the organic material in with a garden fork or hoe.

Pit or Trench Composting

This is the simplest way for composting kitchen scraps.  Dig a one-foot-deep hole.  Chop and mix the food wastes into the soil then cover with at least 8 inches of additional soil. Depending on soil temperature, the supply of microorganisms in the soil and the content of the materials, decomposition will occur in one month to one year. 

Food waste burial can be done randomly in unused areas of the garden or in an organized system. One system is to bury scraps in holes dug around the drip line of tress or shrubs. An English system, know as pit or trench composting, maintains a three season rotation or soil incorporation and growing. Sometimes this is also called Vertical composting. Divide garden space into 3’ wide rows.

Year 1 – Dig a 1’ foot wide trench on the left hand 1/3 of the 3’ area (A). Add compostable materials in this trench and cover with soil when half an inch full. Leave the center 1’ section open for a path (B), and plant your crop in the remaining 1’ strip along the right side (C).

Year 2 – Section A is a path for year 2 allowing time for the Materials to break down. Plant your crop in section B. Section C, where you planted last year, becomes the compost trench.

Year 3 – Section A is now ready for planting. Section B is your trench for composting. Section C is in the second year of composting is it will be the path.