Spilling from truck beds and heaped in large piles at Seattle Tilth Farmworks site on Southeast Lake Moneysmith Road southeast of Auburn, it gently assaults the nostrils of all comers with a rich, funky aroma.

It is compost.

On March 15, Compost Days, an annual, month-long celebration of — as one might guess, compost — and Cedar Groves’ second annual the Big Garden Give, were launched at the farm.

Which is a big deal.

For every bag of compost that Cedar Groves, a Seattle-based composter of food scraps and yard waste, sells during its March 15-to-April 15 campaign, it will donate one bag of compost to community gardens throughout King and Snohomish counties.

For 20 weeks during the growing season, farmers who rely on the compost for their community gardens package up food bags and send them out into the community, creating healthy produce for low-income families.

For the 2014 Big Garden Give event, Cedar Groves donated more than half a mile of compost to local community gardens, about 150 pickup-truck-loads worth.

To start off this year’s Big Garden Give, Cedar Grove will donate 500 yards of finished compost to local gardens to provide free compost to schools and to more than 120 gardens that grow food for low-income residents.

Then, throughout Compost Days, buyers may take steps to bring more compost to these same gardens, including taking an online pledge to compost, or redeeming a coupon for Cedar Grove’s compost. The company will donate a bag of compost to the gardens every time a resident completes one of these steps.

Call it Cedar Groves’ way of saying thank you to all the people who compost at curbside throughout the year. In 2014 alone, local communities using curbside compost carts helped divert from landfills more than 350,000 tons of yard waste, food scraps and other compostable materials.

One-hundred-twenty retailers and 120 local community gardens have signed on to take part in 2015’s Compost Days and the Big Garden Give. At participating retailers, every customer who buys two bags of Cedar Groves’ Compost gets one bag free and earns deep discounts on kitchen food scrap containers and compostable bags.

Cedar Groves’ partners on the campaign are Waste Management, Seattle Public Utilities and King County’s Solid Waste Division.

“Compost matters for a lot of reasons,” said Karen May, of King County’s Solid Waste Division. “If you just start with the compost itself, there are so many benefits to putting compost in your garden or your yard. For one thing, it’s a really good soil amendment to make your soil really healthy. And it’s great that we’re taking our food scraps, and our yard waste, and our food-soiled paper like pizza boxes and turning them into a useful resource, instead of having them in a landfill generating methane.

“Using compost is also a really big opportunity for an everyday person to help combat climate change, because when you put it in the soil, it actually extracts carbon dioxide from the atmosphere and keeps it in the soil. Carbon dioxide is a big contributor to climate change,” May said.

Seattle Tilth Farmworks trains new farmers and sets up marketing outlets for them, including the 16 farmers raising crops, chickens and pigs at the farm.

“It’s an organic operation out here, all of our practices are organic, so a big part of fertility management is the compost, and that’s how we tie into Compost Days,” said Matthew McDermott, program manager for Seattle Tilth Works. “We have a relationship with Cedar Grove — they kindly donate a large amount of compost each year, to the tune of about 150 yards. It gets applied to the fields, which provides nutrients and builds the organic matter for the healthy plants to grow.”

Maria Anderson, who uses the compost to grow mushrooms in an abandoned pool house on the 9-acre site, in addition to vegetables, praised Seattle Tilth Works.

“It gives beginning farmers like me a marketing outlet that we would normally never, ever have. I am able to run my own farm business three or four years ahead of when I would have been able to do it on my own.

“We have shared resources here, tractors, a cooler for all of the produce, stuff that is quite a financial hurdle for a beginning farmer trying to do it on their own.”

Need compost? Buy 2 yards of it and get the third yard free using the Promo Code CD15 at checkouts between March 15 and April 15. Or stop by your local Fred Meyer to get discounts of up to 25 percent on kitchen kits.

For more information, or to get compost coupons, visit http://cedar-grove.com.