Bulletin #1159, How Compost Happens

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compost; photo by Edwin Remsberg, USDA

How Compost Happens (PDF)

Adapted and reprinted with permission from Composting to Reduce the Waste Stream—NRAES 43 (Northeast Regional Agricultural Engineering Service).

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This fact sheet will help you create rich compost to use in the garden, on the lawn and as a soil builder around special shrubs and plants. We include answers to common questions and include a troubleshooting guide to common compost problems.

Q: What can I add to my compost pile?

A: Although almost all natural, organic material will compost, you shouldn’t put everything in your pile. Some wastes, such as fish scraps, bones, butter and meat, will attract pests and may smell. Other items, such as dog or cat manure, contain disease organisms that can survive the compost process and may attract other animals. Plants that are diseased or are infested with insects should not be added to your compost pile because they can cause future problems.

Some types of weeds and grasses (such as quack grass) may not be killed and can regrow. If you add weeds to the pile, be sure the pile heats up enough to kill them. Turning the pile regularly will help.

Easy to Compost Hard to Compost Slow Composters



coffee grounds

egg shells

pine needles

fruit peels and rinds

garden waste

grass clippings






tea bags


wood shavings





fish scraps





cooking oils

peanut butter

salad dressing

sour cream

vegetable oil

wood chips

wood chips, branches, twigs

corncobs, husks and stalks



apple pulp

nut shells

Cut these materials into small pieces and mix them with high-nitrogen materials (manure, fresh grass clippings) to make them decompose faster.

VIDEO: Composting Bins (YouTube)

Q: What are the benefits of making compost?

A: When you compost, you convert vegetable scraps, leaves, grass clippings, and other organic materials into useful, soil-building material. You can use compost in your garden and around shrubs or other plants. Composting reduces the amount of materials that go into landfills, which cuts down on the waste stream.

Q: How long does it take to make compost?

A: Generally, you can create usable compost in two to six months. It depends on materials, temperature, aeration, and management.

Woody materials, such as wood chips, branches, and twigs, may take up to two years to break down unless you finely chip or shred them. If you add these to your pile, the whole pile may decompose more slowly. However, these materials will improve the pile structure and allow air to move through it. This is important if you add dense material, such as manure, to the pile.

Here are some other tips to aid the composting process:

  • Mix materials that break down slowly with materials that break down quickly (food scraps, garden waste, etc.). This allows your pile to heat up faster.
  • Mix materials of different sizes and textures, too. This will make a structurally stable and well-drained pile.
  • Maintain the right carbon-to-nitrogen ratio.

VIDEO: How to Home Compost (YouTube)

Q: Why is the carbon-to-nitrogen ratio important? How can I be sure I have the right amounts of both?

A: Microorganisms in the pile are what make the materials decompose. They use the carbon (C) for food and the nitrogen (N) to build proteins. Without carbon or nitrogen, microorganisms can’t do their job.

You should have about 30 parts carbon to one part nitrogen by weight. This combination will help microorganisms do their job quickly.

This doesn’t mean you have to weigh everything that goes into the pile. Even C and N ratios of 25:1 and 40:1 works well. Just be aware of how much carbon and nitrogen material you add to the pile. In general, coarse, woody material is very high in carbon. Moist, dense material is high in nitrogen (see Compost Materials chart). If there is too much carbon, the pile won’t decompose very fast. If there is too much nitrogen, it will start to form ammonia gas, which can cause odor problems.

Q: Should I add sod to my compost pile?

A: Yes, you may mix sod into your compost pile. Break up small amounts and combine it with other wastes. You can also compost it separately. Here’s how:

  • Put fresh strips of sod in a pile with the roots up and the grass down. Wet it well, and cover it with a tarp to keep the light out.
  • A large pile may take one to three years to decompose.

Q: What if some of the material I put into the compost has been treated with pesticides? Will this cause a problem?

A: If yard waste has been composted at least one year, pesticides should not be a problem. They break down faster in a compost pile than they do in the soil.

Compost Materials that are High in Carbon and Nitrogen (from highest to lowest)



horse manure with litter

horse manure

grass clippings

cow manure

coffee grounds

vegetable waste

poultry manure (with litter)

poultry manure (fresh)

pig manure

wood chips and sawdust




corn stalks

foliage (leaves)

Note: These are listed based on estimates. The amount of nitrogen or carbon may vary depending on the material. For example, brown grass clippings from a dry lawn will have less nitrogen than lush, green grass clippings. If you fertilize your lawn, the clippings will have an even higher nitrogen content.

Compost Troubleshooting Guide

Problem Possible Cause Solution
Rotten smell Excessive moisture (anaerobic conditions) Turn pile or add dry, porous material, such as sawdust, wood chips or straw
Compaction (anaerobic conditions) Turn pile or make the pile smaller
Ammonia smell Too much nitrogen; not enough carbon Add high-carbon material, such as sawdust, wood chips or straw
Pile not heating up Pile too small Make pile bigger or insulate with straw
Not enough moisture Add water while turning pile
Poor air circulation Turn pile
Lack of nitrogen Mix in nitrogen sources, such as grass clippings or manure
Cold weather Make the pile bigger or insulate the pile with a layer of straw
Pile too hot Pile too large Make smaller
Not enough air Turn pile
Pests (raccoons, rats, etc.) Meat scraps or fatty food waste in the pile Remove meat and fatty foods

VIDEO: Worm Composting (YouTube)

Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.

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