Composting on a Grand Scale—the Details

SONOMA COMPOST: COMPOSTING ON A GRAND SCALE

Quality counts at Sonoma Compost. It’s a well-organized operation that starts by sorting materials manually as they arrive because in this case, raw materials matter. Efficient composting requires the proper ratios of two key ingredients—carbon and nitrogen. But not all loads delivered to Sonoma Compost contain similar ratios. Typically curbside cans have more grass (Nitrogen) and homeowner pickup loads contain more brush (carbon). Having ingredients managed from the start, means they can be combined more effectively later.

Also, Sonoma Compost’s organic status hinges on keeping wood and garden debris separate—not all recyclers do this. Some wood discards (plywood and particle board) contain glues. Compost sold for organic agriculture cannot contain wood products. By managing raw materials properly, all of Sonoma Composts products—except Path Mulch—are listed as “allowed” for organic gardeners per Organic Materials Review Institute's standards.

Once materials are sorted, the big machinery takes over. The raw materials are picked up by a 9 cubic yard claw, and fed into a behemoth grinder. The ground materials are ferried around the site by forty cubic yard trucks. Front-end loaders shape the loads into mounds (called windrows) 18’ wide, 7 feet high and up to 600’ in length. Sonoma County produces literally tons of recycled garden materials! At any one time there are at least 18,000 running feet of windrows in various stages of decay.

Maintaining the windrows requires a practiced eye. Optimum moisture and temperature quicken the decomposition process and produce a finer product. Too much or too little moisture can slow down decomposition. In the dry season, water is added as materials are ground; in the long run, this reduces runoff and conserves water. Once the windrows are formed, more water is added using drip irrigation or recycled water from agricultural sources such as wash water from local wineries.

Very little is left to chance. The tops of windrows are even shaped differently depending on the season and water source. Those with drip irrigation have flat tops. If recycled water is added, the windrows are trenched. And in the wet season, the windrows are shaped with rounded tops to shed rainfall.

Temperatures are monitored daily with compost thermometers. To kill pathogens, state regulations require that materials be at at least 131 degrees F for over 15 days during which time the pile is turned at least 5 times. However, temperatures are not allowed to skyrocket as microbial collapse occurs when temperatures exceed 163 degrees. And chemical reactions leading to fires can occur at temperatures exceeding 165.

During the 12-14 weeks after formation, windrows are turned at least once a week. The turnings accelerate the composting process by ensuring that all materials are evenly “baked.” Mulch is ready for sale sooner than Compost. With its higher carbon content, mulch—which is placed on top of soil—is designed to take longer to decay. Compost—which is mixed in with the soil—is ready for sale when it resembles humus—a dark, soil-like product. A variety of different composts and mulches are available.