On common grounds.

Byline: Susan Palmer The Register-Guard

Talk about your hot new coffee trend.

We don't mean the latest iteration of America's favorite caffeinated beverage - your caramel macchiattos or your dulce de leche lattes. We're talking about the humble debris of the coffee world, the spent grounds.

Lane County gardeners have a serious craving for coffee grounds as an additive to their compost piles. The grounds turn out to be rich in nitrogen and when mixed with the right amounts of leaves, grass and other compostable materials may do a better job than manure of converting compost straw to gardening gold.

Oregon State University's Lane County Extension Service has done some experimenting with coffee grounds and plans still more tests on just how coffee affects the soil. The agency also hopes to develop a list of coffee retailers willing to allow people to pick up their grounds.

For the past four years, 13 coffee retailers have worked with Extension compost specialists who placed 32-gallon containers at the shops to collect the grounds.

In that time, gardeners have collected almost 200 tons of coffee grounds from shops in Eugene, Springfield, Florence, Cottage Grove and Veneta, said Cindy Wise, coordinator for the Extension compost specialist program.

But that system hasn't been perfect, Wise said. Some coffee retailers attracted many people who wanted to reuse the grounds, while others got stuck with the heavy containers that not enough people were picking up. The Extension office is proposing that people bring in 5-gallon buckets for coffee retailers to fill.

"This is something anyone would be able to do at participating coffee shops. Just take a clean 5-gallon bucket with a lid, leave it at the shop and then pick it up at the shop's convenience," she said.

The Extension Service office is surveying more than 80 coffee shops in Eugene and Springfield to identify those willing to work with people. Compost specialists will compile a list of participating coffee shops in May or June, Wise said.

For the moment, the Starbucks at 801 E. 13th Ave. in Eugene is part of a pilot project working with gardeners bringing in the 5-gallon buckets, she said.

Wandering Goat Organic Coffee Roasters also provides grounds to gardeners, accounts manager Lucas Willett said. While there's no financial benefit to the coffee roaster, it does fit in with the company's business philosophy, he said.

"It ties in with the sustainability that we're trying to pursue," Willett said.

Gardeners who make their own compost like coffee grounds because they get good results quickly.

"It works great," said Jack Hannigan, who has been using grounds for more than a year at his small organic farm in Pleasant Hill. Hannigan said the grounds push his compost pile temperature up to 150 degrees, hot enough to kill weed seeds and harmful pathogens.

"I can get the piles hotter than I can with manure," he said.

The compost makes a rich additive to the soil for his raspberries, blueberries, rhubarb and potatoes, he said.

The Extension Service's informal trials showed that when 25 percent of compost was coffee grounds, temperatures ran from 135 degree to 155 degrees for at least two weeks, Wise said. Manure didn't sustain the heat as long, she said.

The extension office plans more tests in coming weeks, with plots that have varying degrees of coffee grounds added to the soil and a test plot with no coffee grounds. After letting them sit for six to eight weeks, the soil will be analyzed for nitrogen, potassium, phosphorus and acidity.

"We need to find out how long it takes to break down and how it will affect the nutrients in the soil. Then we'll plant bush beans and see how they look," Wise said. The agency will publish the results in the fall.

Diverting coffee grounds from the waste stream isn't just beneficial for gardeners. Coffee grounds that wind up in the landfill contribute to the production of methane, a greenhouse gas that traps more heat than carbon dioxide, Lane County Waste Management engineer Dan Hurley said. "To keep organics out of the landfill is a good thing for reducing greenhouse gas emissions," he said.

For information onthe composting program, goonline toextension.oregonstate.edu/lane/gardens/compost.