"Clean green" yard trimmings-prunings, lawn clippings and brush collected by landscapers and gardeners-are finding their way into wide use as an agricultural input in California. State recycling mandates have spurred cities to start separate collection of yard trimmings. The increased availability of clean green has motivated farmers to develop innovative ways of using it in their growing operations.

    Small and large row crop growers have started on-farm composting operations. Packaged salad and vegetable processors have set up their own composting facilities, mixing clean green with vegetable culls prior to composting. Large municipal composting operations have sprung up on the urban fringe, making compost products that are inching their way into agricultural markets.

  John Guzik, the Good Humus Man, started his composting business  to take care of the vegetable stems, cores and leaves coming out of the Dole Foods plant in the Salinas Valley. Clean green was added to the mix of compost ingredients in early 1995, when Guzik was offered curbside collected yard trimmings from the city of San Jose.

    "Landscapers up in the Bay Area are harvesting quite a crop of grass and leaves. That crop is a liability to them, but I can make good use of it in my compost windrows," says Guzik. Clean green and vegetable culls are mixed with straw, manure, granite dust and other feedstocks.

    Guzik's first customers were organic farmers, but lately he's seen increased interest from conventional growers. "The conventional farmers started out testing small quantities, using it in combination with synthetic fertilizers. They tested it alongside the steer manure that has traditionally been their mainstay," he says. "They're coming back this year and buying bigger quantities. Compost is a brand new input for them, and they're interested in its disease -suppressive qualities."

    Most growers are applying five to 10 tons per acre pre-plant. Some growers are making compost "teas," and applying them as foliar feeds or injecting them into their watering systems. "A heavy drench at transplant seems to give the plants a good start," says Guzik.

    Guzik's operation was a first for the vegetable processing industry, which had traditionally disposed of the vegetable culls as animal feed. "Three years ago, people laughed at my idea of using vegetable culls as a compost input," he says. "But now two other major producers of packaged salad and vegetable products have entered into composting operations." All three of the operations use clean green collected in San Jose as a compost ingredient.

    The increase in composting has driven an increased demand for the material. San Jose's yard trimmings were delivered to farms and composting operations for free in 1993, but now composters and farmers are generally paying part of the hauling cost.

    Guzik also takes grass clippings and leaves from local landscapers. "They're happy to deliver for free, because they'd have to pay a fee to drop them off at the landfill," he says.

    Farmers and composters who want yard trimmings usually work out agreements with contract processing companies. These companies contract with cities and counties, and receive a "tipping fee" of $15-$30 per ton to cover their costs. They generally grind or screen the material: some companies compost the yard trimmings.

    A key issue for the farming community has been the quality of the product. Will Gehr, technical consultant for Agriculture in Partnership with San Jose, a clean green demonstration program funded by the California Integrated Waste Management Board. says processors have worked hard to minimize the percentage of plastic film and other non-biodegradable materials in clean green.

    "Expansion of the agricultural market for these materials has been very dependent on the processor's ability to listen to farmers and their willingness to meet their needs in terms of product quality," Gehr says.

    Yard trimmings can be ground or screened to different particle sizes. "Composters want material that will provide for some air flow through the pile, but will be pretty well broken down by the end of the composting process," Gehr explains. "Growers who are incorporating uncomposted yard trimmings after harvest want small particle size. Woody prunings and sticks that aren't ground up fine enough can get caught in cultivation equipment and take out a whole row of seedlings."

    Most companies offer yard trimmings that have been ground and processed through a three inch screen. At that size, some sticks will be included in the material. Many on-farm composters remove sticks manually after each turning, and that's an expensive proposition.

    Savvy processors have responded by providing yard trimmings in various particle sizes.

    Mike Thorp, of Santa Lucia Farms in Greenfield, will compost clean green from the Monterey Regional Waste Management District facility in Marina that has been screened three-quarters of an inch. "At that size, most of the garbage gets screened out," says Thorp.

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