Compost the High-Tech Way: Cedar Grove Composting
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Oh, my aching muscles...

By Susan Thoman

If you live in the greater Seattle area and put your garden and food trimmings out at the curb, chances are they wind up at Cedar Grove Composting's facility in Maple Valley, Washington or its newest site in Everett, Washington. There they are transformed into Cedar Grove Compost- that rich, dark humus our gardens need to thrive. Processing over a million pounds of recoverable organics per day,  Cedar Grove has one of  the largest, independently owned composting operations in the United States.

Cedar Grove began operating in 1989 when it was selected to process Seattle's "clean green" yard waste into compost. Diverting this recyclable material was viewed as a way of reducing landfill dependency. Program planners estimated that Seattle residents would generate 13,000 tons of trimmings annually. By the end of 1989 they had, in fact, contributed a whopping 45,000 tons. With the addition of more suburban cities over the years, and the diversion of residential and commercial food added in 2005 throughout the area,  the two composting plants in King and Snohomish Counties have the permitted capacity to process over 400,000 tons of commingled yard and food scraps. The climate impact of this major composting program means the greenhouse gas avoidance  equivalent of powering 40,000 homes for a year or the annual emissions created by 54,000 American drivers

Since the program's inception, Cedar Grove has evolved its technology from open windrows, static piles and aerated static piles to the state of the art membrane laminate technology used in a section of Maple Valley and throughout the Everett plant. With this technology, recovered organics are ground and then covered with a special fabric in 500 ton heaps,  resting on a fully automated aeration/leachate collection trenching system. Each heap is monitored separately by computer, and the temperatures and oxygen level held consistent throughout the process.  At the end of an 8 week cycle, the material is ready for screening, then is aged a bit longer where it further breaks down into rich, quality compost used throughout northwest gardens.

Cedar Grove Compost has been subjected to many tests, most notably by the City of Seattle and the University of Washington. The City tested Cedar Grove Compost for major and minor elements, weed seed germination and heavy metal content. The compost bore significant amounts of major and micro nutrients essential for plant growth and development. Most chemical compounds tested for were not detected and none were present at levels harmful to plants or people. No weed seeds were germinated in the tests corroborating the extensive heat cycle that the shredded material goes through.

Plants grown in compost-amended soil significantly outperformed plants raised in unamended soil, according to a University of Washington field test. Basil plants weighed 16 times more than plants grown in the unamended soil. The test further showed that simply mulching with Cedar Grove Compost improved plant growth by fifty percent. "There are a lot of loyal Cedar Grove users in our local gardening community," said Katie Bach, Horticulturist for Cedar Grove Composting. "We work with expert gardeners and those that are just getting started, and people are  really starting to  understand the importance of using all-natural gardening techniques to keep rivers and waterways clean. Using compost is a big part of that, and our community programs provide good information on how to use compost in a variety of applications."

Composting is nature's way of recycling, replenshing the soil and nourishing  plant growth. The high-tech system at Cedar Grove Composting simply helps Mother Nature to do it more quickly! To learn more, visit   

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