Extension Service Garden Hints

What not to compost

Think twice before putting just any old organic waste into your compost pile.

"The best advice regarding what to compost is probably, 'When in doubt, keep it out,'" said Dan Sullivan, Oregon State University's organic waste recycling specialist. "Home compost piles usually don't get uniformly hot for a long enough time to kill all weed seeds and disease organisms."

If you have a slow or cold compost pile, one that decomposes slowly and doesn't generate much heat, then avoid putting in diseased plants and perennial weeds such as bindweed, sheep sorrel, and grasses with rhizomes, or they may resprout and grow. Keep seed heads of weeds out of the pile as well. Or, be prepared for more weeding in the garden.

Slow compost piles that don't get very hot are great for composting leaves, shrub trimmings and vegetable waste. Adding other materials to the pile may limit your options for finished compost.

It is best to keep manure out of a home compost pile that is not intensively managed, said Sullivan.

"You can't be assured that microorganisms in manure that can cause human disease are killed unless you carefully monitor pile temperatures," warned Sullivan. "To be certain of pathogen kill, the pile must reach temperatures greater than 130 degrees, and the pile must be turned often. Turning the pile moves the cooler material on the edges of the pile into the center where it is hottest.

"You need about five turns during the hot composting phase to assure pathogen kill," he continued. "After each turn, temperatures greater than 130 degrees for three days are needed to kill human disease causing organisms. If you do apply partially composted manure to the garden, be prepared to manage the garden differently."

Sullivan recommended planting root crops like carrots and potatoes, and crops whose edible part contacts the soil, such as lettuce, in a part of the garden without manure applied. If there's a question about pathogen transfer via manure application, careful washing or peeling will remove most of the pathogens responsible for disease. Thorough cooking is even more effective at killing pathogens on garden crops.

Also, keep human, pig, dog and cat manure out of your compost pile, he warned.

"Some of the parasites found in these manures may survive the composting process and remain infectious for people," he said.

Herbicide-treated lawn clippings and plant trimmings will most likely break down into non-toxic compounds, said Sullivan. Herbicides are also inactivated by binding with organic matter in the compost. If you let your grass clippings decompose on the lawn, or let your compost with treated grass clippings sit for a year or more, this will allow for nearly complete breakdown of the herbicides. Plants treated with insecticides registered for use on food crops are safe to compost.

Avoid composting chemically treated wood products, such as sawdust from chemically-treated wood. For example, pressure treated wood may contain toxic arsenic, copper and chromium compounds.

Avoid composting meat and fatty food wastes that attract pests like rats.

By: Carol Savonen
Source: Dan Sullivan

Email this story

Printer-friendly version

News & Garden Archives