COMPOSTING

What is compost?

Compost is organic plant waste that has been transformed into a rich soil fertilizer, providing the nutrients necessary for robust new plant growth and increasing the ability of the soil to hold moisture. The transformation is accomplished by decomposing microorganisms such as bacteria and fungi, as well as larger organisms like worms. Any organic matter that decays and gradually becomes incorporated into the soil is a form of composting; the composting we practice is simply an intensified version of this process.

Why compost?

Yard waste and food residuals account for 23% of the US waste stream, according to the EPA. Composting turns this potential garbage into a valuable resource, reducing the amount of waste going into landfills and saving farmers and gardeners money on fertilizer. Mature compost is a source of organic matter and an excellent fertilizer that improves soil structure. It can be used to enrich the soil of your vegetable or flower garden, around trees and shrubs, and in planter boxes or houseplants. Another bonus to composting at home is you may end up taking out the trash less often!

Want to make your own compost?

Composting is easy! You can make a compost pile in your backyard or indoors, depending on available space.

Compost needs:

• Brown materials (high in carbon) such as dead leaves, branches, sawdust, hay, hedge trimmings, and shredded newspaper
• Green materials (high in nitrogen) such as grass clippings, vegetable waste, fruit scraps
• Water
• Air

Outdoor Composting: Getting Started

• Locate your compost pile in a level, well-drained site that is convenient for you.
• Almost any container can hold compost, such as a plastic garbage can or a homemade wood and chicken wire bin. You can also purchase compost bins from your town’s Department of Public Works, which is generally cheaper than buying from a catalogue. A compost pile can also be built directly on the ground with no bin. More compost bin resources: PA Dept of Environmental Protection and University of Minnesota Extension
• Include both high-carbon and high-nitrogen materials in approximately equal amounts, although you can experiment with the proportions. It can be useful to layer your daily kitchen wastes (high-nitrogen) with a “brown” material such as leaves, hay, or shredded newspaper. A pile with too much carbon will take longer to decompose, while too much nitrogen can result in a bad odor.
• Add some soil, old compost, or a compost activator to introduce the microorganisms.
• Compost needs moisture- but not too much! It should be as moist as a wrung-out sponge. Covering the pile with a tarp helps retain moisture and protect the pile from heavy rainfall.
• Air circulation is important as most decomposing microorganisms are aerobic and need air to survive. Mix easily compacted materials like sawdust with coarser materials. You can also insert tree branches and shake them occasionally to improve air circulation.
• It can be useful to have a two-bin system where food and yard waste can be deposited into one bin that is emptied periodically into a second bin. There it can decompose without the daily addition of banana peels and coffee grounds.

When is compost finished?

Mature compost is dark, cool, crumbly, and earthy-smelling. Finished compost should look more like soil than last week’s leftovers, although cold or passive composting (as most home composting is) may have more materials that are not fully decomposed. These materials can be separated by passing the soil through a screen.

Hot vs. Cold Composting

• Cold composting is low maintenance - simply add ingredients to the compost pile and leave it be. However, it can take months to a year or more for the compost to be ready. This method is best for those who are short on time, have little yard waste, and can wait longer to use the compost.
• Hot composting involves turning or mixing the pile to speed up the decomposition process. Using a pitchfork or shovel, move the contents from the center to the outside. Turning more often produces finished compost faster; mixing every day or two yields compost in about a month, while compost mixed every other week will be done in 1-3 months. The pile needs to be at least 3x3x3 feet in size in order to heat up, but 4 or 5 feet is even better. Hot piles can reach 110-160°F, killing most weed seeds and plant diseases.

Common Problems and Solutions

Putting Worms to Work: Vermicomposting

Worms are a gardener’s best friend and work wonders at composting. Indoor worm composting is ideal for those with limited outdoor space (city-dwellers, listen up). It may sound disgusting at first, but a properly maintained worm compost bin will not attract fruit flies or roaches and does not produce any noticeable smells. It can be placed in a concealed location, like under the sink. Even if you have no use for the finished compost, friends with gardens or potted plants will surely appreciate a gift of compost!

How it works

Worms eat the organic waste and leave castings, turning your kitchen scraps into rich soil.

What you need

• Worms, of course! Red Wigglers or Red Earthworms are the best for composting and can be ordered from a catalogue or bought at a fishing store (they are often used as bait). For each cubic foot of composting bin, you will need one half-pound of worms (approximately 500 worms). Looking for worms? The New York City Compost Project lists places to buy worms.
• A container- a plastic storage bin will do the trick. Make holes in the top and sides with a hammer and nail for air circulation. Line with fine mesh to prevent the worms from escaping. The size should be equal to about one cubic foot per person in the household. In terms of shape, long and wide is better than tall and narrow. Optional- drill holes in the bottom and place on a tray for liquid drainage.
• Bedding- line the container with about a foot of moist bedding such as shredded newspaper, cardboard, leaves, or topsoil.
• Food for your worms- kitchen scraps chopped into 1-2 inch pieces and other compostable materials (see above list), avoiding meat, dairy, and fats

What to do

• Add about 70% brown, high-carbon materials (paper, dead leaves) and 30% green, high-nitrogen materials (kitchen scraps, grass clippings). A layer of shredded paper or sawdust on top will deter bugs and stop smells.
• Move the materials around once a week or every other week for air circulation.
• Keep the bin in a dark location away from extreme temperatures- keep it away from ovens, heaters, and air conditioners.
• The compost should be moist, but not soaking wet- like a wrung-out sponge.

Harvesting the compost

It takes a few months for the worms to turn their food into compost. The finished compost should resemble dark and crumbly soil. The goal with harvesting is to remove the compost while leaving as many worms as possible. Here are two options for harvesting:

• Put the bin in a bright light. The worms like darkness, so they will burrow downwards, and you can take the compost off the top.
• The “migration” method- move the compost to one side of the bin, line the other side with bedding and add food scraps to that side only for a few weeks. The worms will eventually move towards the new food source.

Going on vacation? No problem. These hardy worms can last 3-4 weeks without help. Simply leave a pound or two of food scraps spread on the pile- or enlist a neighbor to feed them and move around the contents of the bin.

Smelly compost bin? If you smell a rotten odor or see many worms trying to escape, there could be several problems- all easily fixed. If there is excess liquid, add shredded paper to absorb the moisture. If the bin is too dry, you can spritz the top with water. A bad odor could also mean you are feeding your worms too much- add a little paper and feed them less. An infestation of other organisms, like fruit flies, can be prevented by freezing the food scraps for 24 hours.

More composting resources

US Environmental Protection Agency Offers a plethora of composting information, including detailed instructions on creating your own compost pile, environmental benefits of composting, and state/regional composting programs.

Natural Resource Conservation Service For hot vs. cold composting, vermicomposting, common problems, and more.

Vermicomposting article from Sustainable Table- Stacey Ornstein offers humorous and practical insights into composting with worms.

California Integrated Waste Management Board Ingredients for compost, suggestions for compost bins, troubleshooting, and more!

References

“Backyard Conservation Tip Sheet: Composting.” USDA Natural Resources Conservation Service.

“Composting: Basic Information.” US Environmental Protection Agency. 7 September 2007.

“Home Composting.” Cornell Waste Management Institute.

“How to Make Compost: A Composting Guide.” Compost Guide. 2004.

Ornstein, Stacey. “Vermicomposting 101.” Sustainable Table. June 2008.

Ward, Susan. “Composting Indoors: Get Worms Working for You.” Garden Guides.

Information compiled by Rose Anderson-Gips, Sustainability Intern, Summer 2008

Content updated by Tina Woolston
twoolston@earthwatch.org
Earthwatch Institute

Photograph © Diane Troppoli