Here in Northern California, Mr. Chambers’s Sonoma Valley Worm Farm produces about half a million pounds of similar compost, an amount he plans to increase in the spring. He loads a long metal bin with cow manure and 300,000 to 400,000 Eisenia fetida, or red wigglers — weighing 300 to 400 pounds. In their wake, the worms leave cattle waste that has been processed into rich and crumbly castings that look like fine peat moss.

It takes six months for a vermicompost bed to become fully mature, by which time a million worms roam the manure. Mr. Chambers continues to add two yards of manure and harvest one yard of worm compost weekly. The finished product is shaved, an inch at a time, off the bottom of the bin. An established bed can go on this way for years.

Both operations pre-compost their manure before they fork it over to the worms. That means piling it up and allowing it to get naturally hot enough to kill unwanted seeds and pathogens like E. coli.

The properties of worm compost are different from fertilizer or manure. “It’s interesting and complicated,” said Rhonda Sherman, an extension specialist at North Carolina State University who has taught vermicomposting around the world for more than 30 years and who holds an annual conference on the subject.

“Certain plants might react well to vermicompost from dairy manure,” she said, “and other plants might react better to food-waste vermicompost.” That has led to “boutique composting,” with different blends for different kinds of plants.

A West Coast company, California Soils, uses worms to break down cardboard waste fibers that are too short to be recycled. The glue used to bind the paper serves as an important source of nitrogen for the worms. “It’s a really good product for nut farmers and stone fruit farmers,” Mitch Davis, a company spokesman, said of the compost, adding that it also helps control nutgall, a fungal disease that afflicts walnut trees.