From Gardener's Supply (

Making a Mountain of Compost

Intervale Compost Products Measures its Success by the Ton

When spring finally comes to northwestern Vermont, there's much rejoicing, especially among gardeners who are anxious to get their hands into the soil. One of the first stops many of us make is to Intervale Compost Products, right down the road from the Gardener's Supply offices and retail store in Burlington.

Intervale Compost Products is an enterprise program of the Intervale Foundation, a nonprofit organization that promotes land stewardship and local organic farming.

The program was begun by Gardener's Supply back in 1988 as a way to recycle leaves that were being put in the city landfill or burned by homeowners. After several years as a low-key operation, the program was turned over the the Intervale Foundation. The Foundation saw an opportunity to produce a bountiful supply of compost to enrich the 80 acres of Intervale farmland that was being converted to vegetable production.

Adam Sherman
Adam Sherman makes mountains of compost at Intervale Compost Products in Burlington, Vt.
Adam Sherman, head of the composting operation since 1997, said that it soon became clear that leaves and yard waste alone wouldn't make great compost.

"There's not enough nitrogen," he said. "Manure quickly came to mind."

In Vermont, most dairy farmers recycle their manure back onto their hay and corn fields, so Intervale Compost Products turned instead to horse manure. In 1994, the operation applied for and received the first-ever commercial composting permit in the state of Vermont. With their commercial permit in place, Intervale Compost Products could now accept food waste from grocery stores, restaurants and food manufacturers.

Initially, it was thought that the fees charged for accepting waste materials would fund the project. But as the product became more well known, the operation found it was making money by selling quality compost.

"It's slowly evolved to where recycling is secondary," said Sherman. "We're now looking at this operation in terms of producing a quality product. There's a benefit to having a diversity of raw ingredients."

Intervale Compost Products
Specially designed windrows make for efficient composting.
Sherman and his crew combine various ingredients to balance carbon, nitrogen, and pH. After these dry ingredients are mixed, the material is scooped up and spread out in six-foot tall, 14-foot wide windrows. Intervale Compost Products has found that windrow composting allows for better aeration and generates the high temperatures that kill pathogens.

Adding moisture is the key to getting the composting process started. The moisture comes from one of the most interesting ingredients in Intervale compost: ice cream waste from the nearby Ben & Jerry's plants.

"We use the Ben & Jerry's waste to irrigate the piles to 65% moisture content," Sherman said. "We start by sculpting the pile so it has a trough in the center. Then a Ben & Jerry's tanker truck comes in and pours a nice milkshake into that trough. At the end of the day we roll it all up together."

Sherman said the sugars from the ice cream waste are quickly metabolized by microbes and the pile's heat increases quickly. The fats in the ice cream are harder to break down, however, and do so at a much slower pace.

"These lucky microbes thrive on a high-fat, high-sugar diet," he said.

The piles get turned every seven to 14 days. A large machine with a high-speed drum mixes the material. The piles are also monitored for oxygen content and temperature. After nine to 12 months, the heat subsides, the pH comes back to neutral and the product is nearly ready for market. At this point the compost is sifted to remove large chunks, leaving behind a fine, crumbly product ready for the customer. Intervale Compost Products is the largest scale bulk composting operation in Vermont, and they sell out of compost every year. Their largest customers are landscapers and home gardeners who purchase it in bulk, right at the Intervale Compost Products headquarters in Burlington. Farmers in the Intervale Foundation's three-year training program can purchase compost at a subsidized rate. The compost is also sold in 20-quart bags at many New England Garden Centers and is available in bulk at the Gardener's Supply retail store in Burlington, Vt. In addition, the 20-quart bags of Intervale Organic Compost are available online at

"This year we sold out of compost in the first week of June. People were heartbroken when they found out," he said. "Our success has almost been our downfall."

There are so many variables to making compost, Sherman said, that it's nearly impossible to forecast how much will be ready at a certain date.

"It's a science but also an art. It depends on biology, chemistry, physics and weather. You can help it along, but compost happens at nature's pace." he said.

The raw materials each have different water content, density and reduction rates. "Forecasting nine months in advance is nearly impossible," Sherman said.

Intervale Compost Products continues to receive much of the raw materials from homeowners. Local residents can drop off yard waste any time during the year. Food waste from local stores and restaurants comes in every day via truck.

"We're a year-round operation," Sherman said. "People bring stuff in all day, in every season." The city of Burlington offers curbside recycling of leaves for a short time in the fall, and those leaves are also brought to Intervale Compost Products.

In order to guarantee a quality product, Sherman is very picky about what ingredients enter the compost facility.

"We only take leaf and yard waste from homeowners," he said. "We can't take street sweepings from the City, for instance, because of oil and fuel waste. Those leaves get landfilled. We always ask questions about our sources."

Quality is the key to the project's success, and Sherman conducts regular testing to ensure the end-product is good.

"We regularly send samples of the finished product to a laboratory, where they are measured for salt, pH, NPK and micro-nutrients. Once a year, we do a full metals and organic chemical analysis," Sherman said.

Though there are no state requirements to disclose compost ingredients, Sherman makes sure this information appears on every bag. "It lets people know what's in it, and that it's a quality product." For more information, please visit the Intervale Compost Products web site.

Last updated: 10/24/15