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posted: 8/31/2014 1:01 AM

Finer points of building healthy compost piles

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By Mary Boldan

Q. Is it necessary to add "compost additive" to my compost pile? What about adding fertilizer or lime?

A. Compost piles must be big enough (at least 3 feet by 3 feet and 4 feet tall) to retain heat before they will maintain rapid decomposition. Add small pieces of material to the pile as the smaller the size, the more surface area provided on which microbes can work. Chopping up leaves with a lawn mower or leaf shredder before they are added to the pile aids considerably. Aim to keep materials slightly wet since they will decompose quicker than dry ones. The pile should have the moisture content of a wrung-out sponge. Since microorganisms need oxygen to function, periodic turning will help keep oxygen in good supply. Turn the compost pile once a week when adding new materials. Be careful about adding lime to your compost, especially if your compost will be given to acid loving plants such as azaleas, rhododendrons, potatoes or blueberries. Adding lime to a compost pile is generally not advised.

People sometimes add nitrogen fertilizer to their compost pile if their Carbon to Nitrogen (C:N) is excessively high in carbon. Compostable materials such as wood chips, paper, and sawdust, for example, have a very high Carbon to Nitrogen ratio. These materials are often known as the "browns" in the compost pile. Some gardeners will add nitrogen fertilizer to help break down the carbon faster in the "browns." Another method is to simply add more organic materials with a much lower Carbon to Nitrogen ratio with "greens" such as vegetable waste, grass clippings, and other green plant matter. For more information on the Carbon to Nitrogen ratio and other tips on composting, visit the following Web site:

Q. What is the difference between regular composting and worm composting?

A. Regular composting, also known as active or hot composting requires that the compost pile and be mixed and be maintained between 130 degrees to 160 degrees Fahrenheit for organic decomposition. Hot composting requires turning!

Worm composting or vermicomposting doesn't require turning. Instead, it involves burying kitchen scraps in a bin filled with worms. The worms devour the scraps and convert them to worm castings, a form of compost. In fact, you don't want the compost to get too hot; otherwise, you will kill the worms. While you can use the earthworms that you find out in your garden, you may have better success by using one of the worms that are specifically raised for vermicomposting, such as red worms. The difference between composting worms and earthworms is that composting worms do a faster job of breaking down organic matter from beginning to end.

Check with your local garden nursery. They may know of some local sources that sell the worms.

• Provided by Mary Boldan. Master Gardener Answer Desk, Friendship Park Conservatory, Des Plaines, open 9 a.m. to noon on Monday, Wednesday, Friday and Saturday. Call (847) 298-3502 or email

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