Composting In Your Backyard

What is composting?

Composting is a biological decomposition of organic wastes by bacteria, fungi, worms, and other organisms occurring under aerobic conditions. During the decomposition process these organisms break down organic waste materials into carbon, nitrogen and other nutrients. The result is an accumulation of dark, friable, partially decomposed material. At home, this process can be managed by placing raw organic materials in a backyard composting structure. Raw materials for composting include leaves, pine needles, twigs, grass, vegetable wastes from the garden and kitchen, vacuum cleaner lint, wool, cotton rags, sawdust, wood chips, shredded wood, egg shells, coffee grounds, tea bags and small branches. Proper management is a key factor, since an unmanaged compost heap may become an eyesore and an odor nuisance.

Why compost?

People compost for a variety of reasons. Composting is a cheap way of providing an enriched organic amendment to the garden. It provides essential plant nutrients, enhances infiltration and improves the soil's moisture holding capability. Compost also builds up the soil structure making it easier to cultivate, benefits soil aeration and makes it possible for course textured soils to retain nutrients normally leached out of the plant rooting zone. Composting is also an environmentally sound way of reducing the solid waste a household generates. Yard waste material makes up about 20% of the volume of collected municipal solid waste and seasonally it may account for up to 80%. Keeping this material out of the waste stream will extend the useful life of existing landfills, slow the need to acquire more land for future landfills and ultimately, save communities money and/or freeing up funding for more important community investments.

Composting Basics

Nature has provided an army of workers who specialize in decomposing organic material. These "critters" - bacteria, fungi, molds, earthworms, insects and other soil organisms eat all types of organic material and in the process break down plant tissue into humus and usable plant nutrients. The process of composting is simply a matter of providing the soil organisms with food, water and oxygen. Anything growing in your yard is potential food for these microbes and larger organisms. These materials provide varying amounts of carbon and nitrogen, which nourish the organisms in your compost pile. An easy way to provide the needed balance of carbon and nitrogen for these organisms is to remember that brown, woody materials, such as autumn leaves, are high in carbon while green, moist materials, such as grass clippings, are high in nitrogen. Microorganisms use the carbon in leaves or woody wastes as an energy source. Nitrogen provides the microbes with the raw element of proteins and nucleic acids to build their bodies. A carbon to nitrogen ratio of 30:1 is ideal for the activity of compost microbes. Table 1 can help you judge the ratio of your compost ingredients. Table 2 provides less specific, but field useful guidance for setting up your compost site. Alternating layers of brown and green materials will yield finished compost in three to eight months. Leaves alone break down in six to 15 months. Grass clippings or food scraps composted alone result in unpleasant odors because they contain more nitrogen than the compost organisms can use. Under ideal North Dakota summer conditions compost piles can decompose in as short as 3 to 4 weeks.

Table 1

Carbon-Nitrogen Ratio

Waste

Carbon:Nitrogen

Food

15:1

Sawdust, Wood, Paper

400:1

Straw

80:1

Newspaper

125:1

Grass

15:1

Leaves

50:1

Fruit

35:1

Rotted Manure

20:1

Cornstalks

60:1

Coffee Grounds

20:1

Alfalfa

12:1

Pine Needles

90:1

Table 2

Sources Of Carbon and Nitrogen

High Carbon (brown ingredients)

High Nitrogen (green ingredients)

Autumn Leaves, Straw, Paper Products, Coffee Filters, Corn Stalks, Wood, Pine Needles

Grass, Weeds, Food, Egg Shells, Coffee Grounds, Tea Bags, Manure, Alfalfa, Blood Meal

Volume

A large compost pile insulates itself and holds the heat of microbial activity. Its center will be warmer than its edges. Piles smaller than three feet cubed (27 cu. ft., 3-4 ft. tall) have trouble holding this heat in the winter, while piles larger than five feet cubed (125 cu. ft., 5-6 ft. tall) do not allow enough air to reach the microbes at the center. These proportions are of importance if your goal is fast, high temperature composting. Large piles are useful for composting diseased plants or trees as the high temperatures will kill pathogens, weed seeds, and insects.

Aeration

Microbes active in composting require oxygen to efficiently break down organic materials. Bulky materials such as leaves, pine needles, chipped twigs, and straw keep the compost pile from settling and allow air to enter. The compost pile should be periodically turned or mixed to incorporate oxygen. Heat is generated by the microbes during the decomposition process. Turning also shifts material from the outer (cooler) part of the pile to the center (hotter). The frequency of turning depends upon the materials being composted, the compost temperature and the moisture conditions, but generally should be done on a weekly basis in warm weather.

Temperature

Temperature is a function of pile size, oxygen and moisture content. To reach temperatures desirable in composting, a pile must be large enough to provide an insulating effect for the interior of the pile. Temperature is an important environmental factor affecting biological activity and composting is dependent on this activity. Each type of organism has an optimum temperature range. Composting is designed to function in the range of 95° Fahrenheit (F) - 160° F. The most effective range for composting seems to be 122° F - 131° F. Higher temperatures of 130° F - 140° F generated in compost may destroy weed seeds and pathogens; however, it is difficult in a home compost system to mix a pile appropriately to bring all wastes to the center and assure complete their destruction. At temperatures above 149° F many of the organisms involved in composting become inactive or die. Turning should definitely be done if the temperature in the center of the pile reaches 140° F or if odors are present.

Moisture

Microbial activity requires adequate moisture, usually 40-60%. At this moisture level, a handful of the compost will feel wet but water cannot be squeezed out of it. The compost pile must be kept moist, but excessively wet materials compact and restrict the movement of air through the pile, start to ferment and cause odor problems. Since moisture evaporates as the pile heats up (a sign of active composting), let rain and snow replace the moisture loss or add water during dry spells. A cover helps retain moisture in hot weather, but never cover compost piles with plastic because this restricts air movement.

Particle Size

Reduction in the particle size of raw materials will increase the speed of the composting process by increasing the surface area available for microbes to attack. To help speed up the composting processes, it is a good idea to chop small limbs, twigs, and garden wastes with a shovel or run them through a shredding machine or lawn mower. The more surface area the micro-organisms have to work on, the faster the materials decompose. Size reduction also reduces the volume of the compost pile, thereby saving space.

Composting Start-up

The following guidelines will get you started, but your own experience will help you tailor a method that best fits your needs.

Build or purchase a compost bin. Check to see if your community has a composting bin distribution program or ordered a bin from a garden catalogue, nursery, or hardware store. Enclosed compost piles keep out pests, hold heat and moisture in and have a neat appearance. Bins are also easily constructed. Bins can be simply made of wire, wood, pallets, concrete blocks, even garbage cans with drainage holes drilled in them. Figures 1, 2, 3 & 4 show examples of compost bins you can build yourself. In urban areas, rodent-resistant compost bins having a secure cover and floor and openings no wider than one-half inch are suggested.

Set up the bin in a convenient, shady area with good drainage. A pile that is about three feet square and four feet high will help maintain the heat generated by the composting organisms throughout the winter. Although a smaller pile may not retain heat, it will compost.

Start the pile with a layer of coarse material such as corn stalks to build in air passages. Add alternating layers of "brown" and "green" materials with a shovel full of soil on top of each layer. Shredding leaves or running over them with a lawn mower will shorten the composting time. Be sure to bury food scraps in the center of the pile. Add water as you build the pile if the materials are dry.

As time goes on, fluffing the pile with a hoe or compost turning tool each time you add material will provide oxygen to the organisms actively breaking down the compost pile. A complete turning of the pile so the top becomes the bottom, in spring and fall should result in finished compost within a year. More frequent turning will shorten the composting time.

Compost Bins That Can Be Built For Home Use

SnowFenceBinSnow Fence Bin

Bins made with prefabricated snow fencing are simple to make and easy to move and store. To build this bin, buy the appropriate length of prefabricated fencing, and fasten two-by-fours as corner posts to the bottom to form a circle.

 

WovenWireBinWoven Wire Bin

One easy to make, economical container requires only a length of woven wire fencing. Multiply the diameter you want for the compost heap by 3.2 for the length of fencing to purchase. Fasten the ends with wire or three or four small chain snaps (available at any hardware store) to make a circle.

 

CementBlockBinCement Block Bin

Compost bins can be made with cement blocks or rocks. Just lay the blocks without mortar; leave spaces between each block. To permit aeration. Pile them up to form three sides of a square container or a three-bin unit. This bin is sturdy, durable, and easily accessible. Keep the bin at least 3 inches away from the walls of your house to prevent deterioration of siding.

WoodenPalletBinWooden Pallet Bin

Covered bins allow convenient protection from pests and heavy rains. Construct bins with removable fronts or sides so that materials can be easily turned. Old wooden pallets can be used for construction. Wire mesh can be substituted for wooden sides to increase air flow.

Composting Problems and Remedies

Symptoms

Problem

Solution

Bad odor

Insufficient air

Turn pile

Dry

Lacking water

Moisten and turn pile

Damp and warm only in center

Small pile size

Increase size and turn pile

Pile not warm

Lack of nitrogen

Add green source and turn pile

Meat

Although meat scraps, fat, bones, grease, dairy products, salad dressing, and cooking oil are compostable these foods ferment or putrefy, cause odors, and can attract rodents and other nocturnal animals that can be pests. Only experts in composting should attempt to compost these materials and they should not be incorporated in the home compost pile.

Ashes Wood ashes are a source of lime and should be added to a compost pile only in small amounts if at all. Large amounts of lime will cause loss of nitrogen from the pile.

Newspaper

Although ordinary black-and-white newspaper is compostable, it has low nitrogen content and decomposes slowly. It tends to compact and restrict airflow unless shredded. It is recommended that newspaper be recycled rather than composted.

Herbicides

Grass clippings and leaves treated with herbicides should not be used as mulch immediately after mowing, but should be composted. The most widely used pesticides degrade rapidly during composting or become strongly bound to organic matter in the compost. Materials exposed to herbicides with active ingredients such as clopyralid and picloram have demonstrated the ability to persist after composting. It is advised not to utilize material treated with these active ingredients for composting.

Temperatures 160° F The larger the pile, the higher the temperature and the faster the composting proceeds, but only up to a certain point. At temperatures higher than 160° F, composting slows down and charring or burning begins. This can become a real problem in dry composts, particularly in the summer.

Completion

When the composted materials look like rich, brown soil, it is ready to use. Apply one-half to three inches of finished compost and mix it in with the top four inches of soil about one month before planting. Compost can be applied as a top dressing in the garden throughout the summer. Compost is excellent for re-seeding lawns, and it can be spread one-quarter inch deep over the entire lawn to rejuvenate the turf. To make potting soil, mix equal parts compost, sand and loam. You may put the compost through a sieve to remove large particles - these can go back into the pile.

This information is available in a color brochure format. To download the brochure follow this link: Composting In Your Backyard Brochure.

Resource reference:

Compost Tips For The Home Gardener
Home Composting: A Guide to Composting Yard and Food Waste
Persistent Herbicides In Compost
Composting Practices

For additional information contact:

Steve Tillotson
Division of Waste Management
918 East Divide Avenue, 3rd Floor
Bismarck ND 58501-1947
Telephone: 701.328.5166
Telecopy: 701.328.5200


Division of Waste Management Home Page

Updated: 8 Apr. 2008