CORVALLIS, Ore. – If your compost pile at home isn't getting hot, don't worry. It's okay if your yard debris and kitchen waste are far from steamy.
Cool, slow composting is easier to do than hot composting, will break down eventually and may have hidden benefits, according to Oregon State University soil scientist Dan Sullivan.
"Slow composting is often the best method for people who do not have time to tend a hot compost pile, which takes more care and a more precise recipe," said Sullivan. "It's an easy and convenient way to turn yard wastes into a useful soil amendment."
Decomposition requires microorganisms, moisture, air, temperatures above freezing and time. To make slow compost, simply mix yard trimmings into a pile and let them sit.
"West of the Cascades, Mother Nature will provide plenty of moisture," Sullivan said. "You don't need to worry about the proper carbon-to-nitrogen (C:N) ratio. The C:N ratio only affects the speed of composting. If your pile is woody (high C:N) it will just decompose slowly."
Don't worry about adding a commercial inoculant or compost. "Sufficient decomposer bacteria and fungi are present naturally in yard trimmings and fruit and vegetable wastes," he said.
Sullivan practices slow, or cool composting in his own backyard.
"Into my pile go the fall leaves and woody prunings from the yard," he said. "The bigger branches provide pathways for air to enter the pile. Sometimes I stir the pile by lifting up on the big branches." By May or June, the fall leaves look like compost and only the coarse leafless branches remain.
"I find lots of night crawlers at the bottom of the pile," Sullivan said. "I use the compost and night crawlers in the garden and contribute the remaining branches to our curbside yard waste pickup bin."
To avoid attracting possums, raccoons and skunks to the pile, bury fresh fruit and vegetable scraps way in the center of a big compost pile.
"If you have a critter problem, you might want to compost the fruit and vegetable scraps in a critter-proof container or bury them in a well-drained part of the garden," he said. "The fruit and vegetable scraps contain a lot of water and don't result in much compost. The main point is to keep fruit and vegetable scraps out of the trash."
There are drawbacks to slow composting. It doesn't produce heat needed to kill most weed seeds, and it is best to keep troublesome weeds out of the pile.
Soil-borne plant disease organisms that cause root rot also are not killed in slow composting. To limit spread of soil-borne disease, apply slow compost to a small part of the garden, rather than spreading it over the entire garden area.
Cool composting can have unexpected benefits.
"Our family added our rotten pumpkins to the slow compost pile in the fall and found a ready made pumpkin patch the following spring," Sullivan said. "The pumpkin seeds emerged earlier than I usually plant them in the garden. We let them grow on the old compost pile, and they produced a good harvest. I guess that is the ultimate in recycling."