ANR-794 Reprinted Aug 1997. By J. David Williams, Extension Horticulturist, Assistant Professor, Horticulture, and James O. Donald, Extension Agricultural Engineer; Professor, Agricultural Engineering, both at Auburn University, and Tony A. Glover, Extension Agent.

Commonly Asked Questions About Composting

Can you add kitchen scraps to a compost pile?

Yes, almost any organic kitchen waste like food scraps and paper can be composted. However, meat, bones, and foods high in oils and fat can generate foul odors. They are also attractive to a wide range of insect and animal pests. Vegetable and fruit scraps, egg shells, and coffee grounds are much better to compost.

Will weeds added to the compost pile increase weed problems later in the garden and flower beds?

Most weeds and many weed seeds will be killed by the heat generated in the compost process. Weeds that have not gone to seed can be added to the compost pile with some confidence that they will not be a problem. However, weeds that have large storage roots like nutsedge, florida bettony, or greenbriar should be left out or dried and chopped up before composting to reduce the chance of survival during composting. Frequent turning of the pile promotes more uniform and thorough decomposition and therefore decreases risk of survival of weeds.

Is it absolutely necessary to turn a compost pile?

No, but, by turning the pile, fresh organic matter, in essence food for microorganisms, is more uniformly distributed to those organisms. This promotes more rapid and uniform decomposition than simply letting the pile rot. A frequently turned and carefully managed compost pile can decompose in weeks while a neglected pile can take a year or more to produce a finished compost.

What can you do about fireants in the compost pile?

Pesticides are available to control fireants if they are present and pose a problem or hazard to you. However, fireants generally avoid places that are disturbed, so a compost pile that is turned often will not be an attractive place for fireants to build a home.

Are composted pecan leaves safe to use in the garden?

Although pecans are related to black walnut, which secretes a compound that is deadly to tomatoes and some other garden plants, no evidence supports a cause for concern about using composted pecan leaves in the garden. Any toxic substances in pecan leaves or any other kinds of leaves that could injure garden plants are thoroughly leached out or broken down during composting.

Can you use plant material that is diseased in a compost pile?

High temperatures that develop during composting kill many plant pathogens. Also, organisms that attack plant pathogens thrive in the compost pile and can reduce potential plant diseases. As long as the pile is turned so the whole pile has a similar chance to heat up and be exposed to those microbes that suppress diseases, the pathogens can be reduced to a level that should not be a problem in the garden. Thorough and well-managed composting is most important if diseased plants are added to the pile.

Can you compost yard waste that has a waxy coating and thorny waste, such as evergreen shrubbery clippings, and rose and holly waste?

Yes. However, plant material with a waxy coating may take longer to decompose. Shredding these materials will help break apart the waxy cuticles, exposing more surface area to the microorganisms for faster decomposition. The only problem with thorny waste is that it may be difficult to handle without gloves.

Do you have to have some kind of a structure to make compost?

No. Compost can be made in an open pile. A structure helps keep the pile neat and in a size and shape that will allow it to heat up in the middle and decompose faster. It will also hide the waste from the view of you or your neighbor. Where multiple bins are used, turning the compost from one bin to another is a convenient and effective way to manage the compost pile.

What size should a compost pile be?

A compost pile should be at least 3 to 4 feet high for it to adequately heat up in the middle. The width of the pile can be any size you can manage, but a general recommendation is 3 to 4 feet wide. One or two 3 x 3 foot compost bins are adequate for handling most, if not all, of the yard waste from a city lot.

Are odors a problem in a compost pile?

Although not usually a problem, under some conditions odors do occur. The most common problem that causes a compost pile to smell bad is lack of adequate aeration in the pile. This could be remedied by mixing in materials that are coarse and will help create air spaces in the pile. Also, smelly symptoms can be due to too much moisture and high nitrogen content in the pile. Add waste that is higher in carbon: the dryer, brown (woody) materials.

Is there any problem with composting newspaper?

No. True newsprint, the inexpensive paper made from wood pulp, is a good source of carbon if shredded and mixed with other materials. The inks used with newsprint, even colored newsprint, are considered non-toxic.

How can you tell when the compost is "finished"?

When the compost appears dark, crumbly, and looks much like soil, it is ready to use. Any large, woody pieces still not completely decomposed may be sifted out, if desired.

What are compost "activator or starter" materials?

Compost "activators" are dehydrated bacteria in a package. The numbers of bacteria existing on the organic material and soil used in a compost pile are more than enough to start the composting process. These bacteria also multiply very rapidly, so it is probably not necessary to use such a product.

Do you ever need to add fertilizer to a compost pile?

If you have a good mixture of green and brown waste materials (an average carbon to nitrogen ratio of about 30:1), you should not need to add fertilizer to the pile. However, if you have high carbon materials, a nitrogen source of fertilizer could be used to hasten decomposition.

Should limestone be added to compost piles?

There is no need to add lime to a compost pile. Too much lime, in fact, could create a loss of available nitrogen in the pile. Finished compost generally has neutral to slightly acid pH.

Is it all right to mix pet (dog or cat) or human wastes into the compost pile?

It is not recommended to add pet or human wastes to a compost pile. Studies have shown that there is a potential for health problems to occur where compost with pet waste has been used in vegetable gardens. Human waste has the potential for transmitting diseases as well and therefore should not be used. If you have to deal with pet waste, bury it away from garden areas.

Should a compost bin have a top on it?

Two reasons you might want to cover compost are to control the amount of moisture added to the pile and to keep out rodents and pets. However, these two factors are not always a problem. Unless we have an unusually wet season, a compost does not generally get too soggy. If you don't add scraps of meat, bones, or grease, pests aren't a serious problem.

Is it all right to mix fireplace ashes into the compost?

A limited amount of wood ashes can be used in the compost pile. Wood ashes can add potassium and other nutrients, but they also have the capacity to raise the pH very rapidly. Overuse could create problems with the compost pile.

For more information, contact your county Extension office. Look in your telephone directory under your county's name to find the number.