Can you explain hot composting?

Answer: When the weather is good for growing plants, it is also good for composting. However, because composting generates its own heat, the composting season is often longer than the growing season.

Composting is a simple process that combines the nitrogen and carbon in the materials you’re using with moisture and oxygen to create an ideal environment for the microbes and other organisms that are doing the work. When you combine those ingredients with a little elbow grease, you can use “hot” composting techniques to support microorganisms that get results in a relatively short period.

In order for the compost to generate enough heat for hot composting, most growers suggest that piles be at least 3 feet high by 3 feet wide and 3 feet long. If you don’t have enough materials for a compost pile that large, store your materials until you do. If the pile is larger than 5 feet by 5 feet by 5 feet, however, the microbes at the center may not get enough oxygen.

If your compost pile is sitting directly on the ground, it’s a good idea to start with some woody materials to provide nooks and crannies for oxygen to get to the compost.

Combine nitrogen-rich green materials with an equal amount of carbon-rich brown materials. Some people prefer to mix the two together, and others prefer to layer them on the compost pile. If you do layer them, make the layers 2 to 4 inches deep. Be sure that your compost pile is well aerated. “Fluffing” or turning the compost pile — essentially moving the materials on the inside of the pile to the outside and vice versa — will serve that function, and there are other strategies such as punching holes in the pile. There are specially designed tools for making aeration holes in compost piles, such as rods with small “wings” at the tip that collapse against the rod as it is being inserted. When the rod is removed, the compost pulls against the wings and unfurls them, which creates a larger hole.

Keep checking the moisture content of the compost pile throughout the season. The compost should be moist, but not saturated. A good rule of thumb is that it should feel about as moist as a wrung-out sponge. The center of the compost pile will heat up, sometimes as high as 160 degrees Fahrenheit on the inside of the pile, and then begin to cool. There are commercially available thermometers for compost piles, or you can simply use your hand to see if the compost is warm to the touch. Turn the compost periodically, swapping the material on the inside of the pile for materials from the outside. This step plays a big role in how quickly the compost will be ready. Depending on conditions, a pile that is turned every day or two can produce compost in as little as a month. A hot pile that is turned every week or every other week may take a few months to produce results.

Ready to dig in deeper? Check out ATTRA’s Composting–The Basics. This publication provides a foundation of information for those interested in composting. It addresses a wide range of topics, from the materials that are needed to begin a compost pile to techniques for successfully managing the composting process. A troubleshooting list describing common problems and how to address them also is included. In addition, the basics of vermicomposting — using worms to generate compost — are described. Finally, the publication contains an introduction to composting for small agricultural operations such as market gardens.