Rapid or "hot" composting is a great option for impatient gardeners who don't want to wait the 6 to 12 months it takes for most compost piles to mature. Done right, hot compost can be ready in as little as 14 days.
It does take a little extra work, requiring you to shred the materials and manage the pile more actively. But you can't beat the timeline. Here's how to do it:
1. Use equal parts by volume of green and brown materials
This will deliver the 30:1 ration of carbon- to nitrogen-rich ingredients you're after. Brown materials include dead leaves, twigs, wood chips, brown-paper bags, newspaper, cereal boxes, milk cartons (rinsed) and cardboard boxes. Green materials would be grass clippings, spent flowers, and kitchen scraps—fruits, vegetables, coffee grounds, and eggshells (no meat or milk products). For a complete list of what can go into a pile, check out the composting section on the Environmental Protection Agency's website
2. Chop them small, into ½- to 1½-inch pieces
This gives the microbes lots of surface area to get to work on. Use a reel mower to run over soft plant material or pruning shears to cut it up. A chipper might be needed for tougher stuff, like twigs and branches.
3. Layer greens and browns in a pile at least 36 inches square and 36 inches high
Pile the materials in thin layers, alternating greens and browns. Make sure paper and grass clippings don't clump up. Using a bin with a lid helps retain heat. If yours has no lid, you can add a piece of plastic on top. You can find instructions on how to build a compost bin here. Just be sure to size it right for hot composting.
4. Add water
Materials need to be kept moist, but not wet. They should feel like a wrung-out damp sponge. If they become soggy, they will develop a bad smell. If they are too dry, decomposition will be slow or will not occur at all. Add water as needed to keep the pile moist.
5. Turn the pile
The pile should heat up within 24 to 48 hours; if it doesn't the pile is too wet, too dry, or needs more nitrogen. Use a thermometer with a probe to take the temperature at the center of the pile: 160-degrees F or slightly lower is ideal. Any higher and it will kill the active microorganisms needed for decomposition.
Use a garden fork or shovel to turn the pile, moving the material in the center to the outside. This prevents the pile from overheating and activates the outer layers. If the pile is turned every day, it should take two weeks or a little longer to break down into dark-brown, fresh-smelling, crumbly compost.
Interested in learning more? Find the original paper published by University of California professor Robert D. Raabe here