Backyard Composting

Part 3: Health and safety questions

Introduction

Part 1:
Composting basics

Part 2:
How to make compost

Part 3:
Health and safety questions

Part 4:
Using compost in your yard

Composting coffee grounds

Are there any plant materials to keep out of a compost pile?

If you are composting by the slow method, keep diseased plants and seed heads of weeds out of your compost pile. For any compost, avoid coarse, woody materials because they break down slowly and make the pile hard to turn.

Some plants contain compounds that slow microbial decay. Western red cedar, often used for fence posts because of its resistance to decay, can break down slowly in compost piles.

Are there other materials to keep out of a compost pile?

Do not add meat or fatty food to the compost pile. Do not add dog, cat or pig feces.

Can a compost pile catch on fire?

A compost pile will only ignite if it has a very hot zone next to a dry zone. Fires will not start in moist piles or in small, backyard piles.

Can I use manure in my compost?

If you use fresh manure in a slow compost pile or directly in your garden, a small risk exists that disease-causing pathogens will contaminate garden vegetables. To reduce the risk of disease, allow at least 60 days between applying manure and harvesting any vegetables that will be eaten without cooking.

The risk is greatest for root crops such as carrots and radishes, or leaf crops, like lettuce, where the edible part touches the soil. Careful washing or peeling will remove most of the pathogens responsible for disease. Thorough cooking is even more effective at killing pathogens on garden crops.

It is best to keep dog, cat, and pig manure out of your compost pile and garden. Some of the parasites found in these manures may survive the composting process and remain infectious for people.

Additional information about using composted manure safely is available in the Livestock Manure Composting section.

Are herbicides a problem in compost?

Some people are concerned that herbicides (weedkillers) in compost-amended soil can harm plants. Most herbicides in home compost piles come from lawn clippings. The warm temperatures in a compost pile accelerate herbicide breakdown to nontoxic compounds. Binding with organic matter in the compost also inactivates herbicides. Breakdown and binding reduce the risk of herbicide damage. To avoid herbicide problems:

• use fewer (or no) herbicides,
• return treated grass clippings to the lawn rather than compost them,
• use herbicides that break down quickly,
• let your compost sit for a year or more, allowing nearly complete breakdown of the herbicides.

What about commercial composts?

Composts are also commercially produced on a large scale from yard debris (woody prunings and grass clippings) and food waste. They vary widely in nutrient availability. Composts that look woody are usually low in nitrogen. Like sawdust, they require additional nitrogen when mixed into the soil.

Commercial composts are screened to separate particle sizes. Mix fine compost with soil to increase organic matter. Use coarse compost for mulching trees and shrubs.

Part 4: Using compost in your yard