At Heritage Farm, a handful of buckets filled with grass, coffee grounds and fallen leaves are helping answer a deceptively simple question: What makes the perfect compost?
For approximately six months, Pete DuBois, environmental outreach specialist at Clark County Public Works, has been leading a team to test various compost mixes to find the optimal balance of carbon and nitrogen materials. This effort combines scientific research, practical experimentation and public education. In Washington, particularly in Clark County, composting initiatives have emerged as a regional leader in instructing residents on converting everyday waste into beneficial resources, reducing food scraps in landfills and returning nutrients to the soil.
“Composting is a science and an art, and so if you just take things that will rot and throw them on the ground, they will rot and so it's just a matter of time,” DuBois said.
At its core, composting is the process of building a healthy pile of organic material that breaks down into nutrient-rich soil. That starts with layering carbon-rich “browns,” including dried leaves, cardboard or even newspaper, with nitrogen-rich “greens,” such as grass clippings, food scraps or coffee grounds. Add moisture and oxygen, and microbial life begins to thrive, breaking everything down over time.
“Taking materials that are easily gathered and transforming them into this living soil for creating healthy food, really nutrient-dense food,” he said. “For instance, these coffee grounds were all going to the landfill. It is almost a fertilizer in itself with nitrogen, phosphorus and potassium.”
The trick to composting has been a simple rule of thumb: a one-to-one ratio of browns to greens by volume. But recent testing suggests that balance may be shifting.
Now, the team is finding that a roughly 2-to-1 ratio of carbon to nitrogen materials by volume may produce better results. Their goal is to create finished compost with an ideal carbon-to-nitrogen ratio of 25-to-1 by weight, a benchmark widely considered optimal for soil health.
DuBois and his team continue to put their theory to the test. Last Tuesday, they built a compost mix using 13 buckets of slightly damp mowed leaves at about 5 pounds each, totaling 65 pounds of carbon-rich material. They added 2.88 buckets of three-day-old grass at about 10 pounds per bucket, totaling 28.8 pounds, along with 2.44 buckets of dry espresso coffee grounds at about 30 pounds per bucket, totaling 73.2 pounds of nitrogen-rich material. The coffee grounds, though brown in color, are considered “greens” due to their high nitrogen content.
By volume, the mix worked out to roughly a 2.44-to-1 ratio of carbon to nitrogen materials, reinforcing the team’s shift toward a 2-to-1 layering approach for practical composting. For most home composters, that translates to using about two buckets of browns for every one bucket of greens.
“Yeah, so this will get sent to a soil lab … We've done that in the past, so we've got some pretty good baseline information,” DuBois said. “That just helps us with the science part of it. We're pretty good at the art piece.”
By finding a reliable “recipe,” in volume of greens and browns, DuBois hopes to give residents simple, proven methods they can use at home.
“What we're trying to do is create a recipe that we know works,” DuBois said.
The tested soils DuBois has helped produce are used to help produce vegetables on the Heritage Farm site. For gardeners, this can showcase the advantage of homemade compost. Unlike store-bought products, which may contain unknown materials or contaminants, backyard compost is made from known materials and avoids synthetic chemicals. It also keeps food waste out of landfills, where it would otherwise produce methane, a potent greenhouse gas.
“We know all of these products contain minerals … We're just gaining more knowledge. Then we know how much compost to use, how much compost you need to make,” he said.
The sample will be tested to confirm whether it reaches that 25-to-1 balance, and will help DuBois make further adjustments. Meanwhile, the bin itself will become a teaching tool during the county’s first “Gardening with Compost” workshop this spring.
Spring workshops give gardeners the tools to grow their skills
Public Works will host a lineup of spring workshops aimed at helping residents reduce waste and build healthier soils:
At Heritage Farm, DuBois showed The Reflector an abundance of worm compost bins. The demonstration showcased how the worms naturally help turn food scraps into compost.
“Worm bins are just a … different way to make fertilizer in a small contained space that you can do in your garage,” DuBois said. “You can do it, frankly, in your house. You can do it outdoors as well, and it creates a more concentrated fertilizer product that is super black and rich.”
The “Low Waste Chef” workshop focuses on preventing food waste before it starts, with tips on storage, meal planning and understanding food labels. “Backyard Composting” covers the basics of building and maintaining a pile, including sourcing enough material. Public Works’ recycling workshops explain what belongs in curbside bins and what should be handled elsewhere, helping reduce contamination. “Green Cleaning” teaches residents how to replace chemical-heavy products with simple household alternatives.
The new Gardening with Compost workshop focuses on the science and art of composting. Participants will also learn how fertilizer needs vary by crop, with plants like corn requiring significantly more nutrients than lower-demand crops.
“It’s (about) understanding how this product can be used to support your gardening without needing to bring in products that you either pay money for or chemicals, ideally, that are not synthetic,” DuBois said.
Participants will learn how much compost different crops need, when to apply it and how its slow-release nutrients can support soil for years, unlike conventional fertilizers that quickly dissipate.
“One of the differences that we want folks to understand is that with our compost, it is broken down, but it's continuing to decompose,” he said. “So when we spread it, it could continue to provide nutrients for up to five years.”
Residents can learn more or sign up for workshops at wcnorthwest.com/composter-recycler-spring-workshops. The times and locations will be posted at a future date.
