What to Know About Compost Science
Left on its own, all organic matter will break down through the action of hungry bacteria, fungi and other larger creatures such as worms, sow bugs and centipedes. These "decomposers" consume decaying compost pile materials, producing heat and carbon dioxide. What started as leaves or food is converted into stable humus, which has a mild, earthy odor and whose texture and nutrients improve the quality of soil.
Paying attention to the needs of this team of decomposers will allow you to manage a pile to produce compost faster and without odor or pest problems. Remember, a compost pile is alive, so factors such as moisture, oxygen, particle size and the materials you feed the pile will affect its performance.
Compost Pile Ingredients
All organic materials can be composted. But for backyard composting, follow these guidelines:
YES!!! You can put these materials in your backyard bin or pile:
- leaves and brush
- plant cuttings
- grass clippings
- fruit scraps
- breads and grains
- coffee grounds and filters
- tea bags
- egg shells
- wood chips
- wood ash
- old potting soil
- cut flowers
- food-soiled paper (napkins, paper towels)
NO!!! Don't add these materials to your compost:
- meat scraps
- fish scraps
- dairy products
- fats or oils
- dog feces
- kitty litter
- weed seeds
- charcoal ash
- non-organic materials
Layering / Mixing
All organic materials contain carbon and nitrogen in varying proportions. In general, green, wet materials such as grass clippings, food scraps and plant cuttings contain a higher proportion of nitrogen than brown, dry materials such as wood, paper and autumn leaves.
To create ideal conditions for composting, layer or mix materials in your compost pile so that you have roughly equal amounts of high nitrogen greens and high carbon browns. A pile with more browns will still turn into compost, but it will take longer. If you add too many greens, your pile may generate odors.
To avoid possible odors or pests, bury food scraps under browns such as leaves, brush, wood chips or finished compost.
high nitrogen GREENS:
- grass clippings
- plant cuttings
- fruit and vegetable scraps
high carbon BROWNS:
- fallen leaves, twigs
- wood chips, sawdust
- used napkins and paper towels
- soil or finished compost
Air and Water
The microorganisms in compost need oxygen and water to survive.
To make sure that air can penetrate to the center of your pile, it should not be larger than 5 feet high by 5 feet wide. You can also layer your pile with coarse materials to help air circulation; or you can aerate your pile by turning or mixing it periodically. Turning requires extra effort, but will accelerate the compost process.
Your pile should be about as moist as a wrung-out sponge, but not soggy. You may want to water it periodically during a dry spell, or after adding large amounts of dry materials.
You can make compost in as little as three months, or the process could take as long as one year. Each of the following measures will speed the composting process:
- layering your pile with the proper proportion of greens and browns
- turning your pile and keeping it at a proper moisture level
- cutting up large items such as houseplants, branches, or grapefruit rinds before adding them to your pile.
If you have ever bought and used peat moss, wood chips, manure, or topsoil then you already know how to use compost. Mix compost into flower and vegetable beds; blend it with potting soil to revitalize indoor plants; or spread it on your lawn as a fertilizer. Use coarser compost as a mulch around trees and shrubs.
Note: If you make compost with plant cuttings or grass clippings that have been sprayed with pesticides, you may want to avoid using the compost on edible crops.