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Yard waste makes up a third of municipal solid waste, behind paper products and food. Estimates show that the average lawn produces about 1,500 pounds of grass clippings each year. A mature tree drops about 3,600 pounds of leaves annually.
With lawn mowing and gardening season in full swing, it is a good time to look at how to reduce yard waste, said University of Missouri Extension horticulture specialist David Trinklein.
Missouri law bans yard waste from landfills. Yard waste takes up valuable space and generates methane, a potent greenhouse gas, as it decomposes.
“Finding an environmentally sound way to dispose of yard waste has become even more important,” said Trinklein. “To promote good environmental stewardship, the Composting Council Research and Education Foundation set May 5-11, 2019, as International Compost Awareness Week.”
Fortunately, turning lawn and garden waste into compost takes little more effort than bagging and hauling it away, said Trinklein. Good compost consists mostly of decomposed or partially decomposed plant and animal residues. It improves the physical condition and fertility of soil when added to the landscape or garden. It also benefits poorly drained soils low in organic matter.
“Compost speeds natural decomposition under controlled conditions,” he said. Raw organic materials turn into compost by the action of organisms in the soil. Bacteria increase rapidly during the first part of decomposition. Then, actinomycetes (filamentous bacteria), fungi and protozoans go to work. After much of the carbon in the compost is used and the temperature of the pile falls, centipedes, millipedes, sow bugs, earthworms and other organisms continue the process.
As microorganisms decompose the organic materials, their body heat raises the temperature in the pile dramatically. The center of a properly made compost pile should reach a 110 to 140 degrees Fahrenheit in four to five days. The pile begins “settling,” a sign that it is working properly. The pH of the pile is acidic at first, at a level of 4.0 to 4.5. When completed, the pH rises to about 7.0 to 7.2.
Heat kills some weed seeds and disease organisms in the pile’s hottest area. Trinklein recommends turning the pile properly to move heat to all of the pile. See the MU Extension publication “Making and Using Compost,” available for free download at extension.missouri.edu/p/g6956(opens in new window).
Proper composting should kill harmful microbes such as E. coli and Salmonella. Monitor the temperature of the pile. Compost from piles that do not heat to 140 degrees should be treated as “raw” compost. Food safety regulations require a 150-day waiting period after applying raw compost before vegetables can be harvested.
Compost should be dark and crumbly when ready to use, Trinklein said. The original composted items will not be recognizable. “Compost contains nutrients. However, its greatest benefit to gardeners is the improvement it makes in soil characteristics. Consider it a valuable soil amendment rather than a fertilizer.”
Organic matter in compost improves heavy clay soils by binding soil particles into “crumbs.” This makes the soil easier to work and improves aeration, root penetration and water infiltration. It also reduces crusting of the soil surface. In sandy soils, additional organic matter helps soil retain nutrients and water. Compost increases activity of soil microorganisms that release nutrients and other growth-promoting materials.
Add compost each year to build good soil, said Trinklein. The best time to add compost to the vegetable or flower garden is during fall or spring tilling. Add it to the soil when planting trees, shrubs, annuals or perennials. Compost serves as an excellent mulch or top-dressing around flowers, vegetables, shrubs and trees. If used as mulch, the compost need not be completely finished.