How it’s made

Science, systems, and a whole lot of microbial magic!

We make our compost using a process known as static aerated pile composting using local ingredients (what we call feedstocks) that would otherwise go to a landfill. We receive food scraps and leaves from local residents and area businesses.

These materials are mixed with wood chips, select local farm manures, and small amounts of wood ash to achieve a consistent and biodiverse recipe.

Micro-organisms, or microbes, are responsible for the seemingly magical process of composting. Microbes are already present in all of the feedstocks that come into GMC. Once mixed with the right ratio of nitrogen (“green” ingredients) and carbon (“brown” ingredients,) plus the right amount of water and oxygen, the microbes really go nuts!

Moisture is essential for microbe movement and reproduction. Oxygen is essential for microbe activity because microbes are consumers of oxygen. In the absence of oxygen, the entire chemistry changes and composting slows or ceases. Our job is to create the perfect conditions for billions of microbes to do the job they are so good at doing—breaking down organic material into nutrient-rich compost.

Wicked good compost, in 7 steps

Step 1: Blending

We blend the proper ratio of ingredients with our industrial Windrow Turner to achieve a carbon to nitrogen ratio of about 25-30 to 1, which is ideal for composting. Blending the feedstocks ensures a more uniform mix of all of these components, and a greater surface area for the microbes to nibble on, thus speeding up the composting process.

Nutrient-rich water from our underground storage tank is added to each batch to achieve ideal moisture at 60% to 65%.

Mixed material is loaded into covered bays embedded with perforated aeration pipes and then capped with a layer of wood chips to trap odors and moisture.

Step 2: Aeration, part I (2 weeks)

Electric blowers are used to deliver oxygen to microbes, (a more energy-efficient method than the traditional method of turning piles with heavy equipment.) Embedded pipes in the floor of the bay are connected to variable speed electric blowers.

As the temperature rises above 104°F, the microorganisms–mainly bacteria–found in this small ecosystem change from mesophilic to thermophilic. These “heat-loving” microorganisms break down sturdier materials like plant stems, leaves, and roots as well as animal proteins and fats.

Pile temperatures are carefully monitored to ensure that all material meets a minimum of 131o F for at least three days—the state and federal standards. Weed seeds and potentially harmful human and plant viruses, fungi, and bacteria cannot survive these high temperatures in which thermophiles thrive.

Adjustments to timers on the blowers allow us to maintain ideal composting conditions at all times. Hotter is not necessarily better with composting. Pile temperatures tend to rise very quickly, often to well over 150o F in 24 hours within the first day or less, (even in the dead of winter!) Temperatures much above 160 F can actually decrease the rate of composting by killing off key populations of microbes. Temperature probes at different locations and depths on each pile send data to a computer.


Material is removed from Phase 1 with a bucket loader, mixed in process, and piled into a windrow onto center of pad. This ensures that the outside (less decomposed) part of the pile gets turned into the center for further decomposition by the thermophiles.

The pile is moistened with “clean” water to bring it back up to 60-65% moisture.

Step 3: Aeration, part II (3 to 4 weeks)

The pile is then moved (and mixed again in process) to the uncovered side of the concrete pad for a second round of aeration.

Temperatures and oxygen continue to be monitored via probes to maintain optimum levels. Continued thermophilic decomposition occurs in phase 2, with temperatures averaging 135°F.

Step 4: Screening #1

Compost is put through an industrial screener with a 2” screen.

The “overs”—things like utensils, plastic, rocks and wood chips–are removed at this stage. Screened wood chips and other organic materials are recycled back into future batches.

Step 5: Curing (3-4 months)

Screened compost is hauled to a curing area where it is made into long windrows. The windrows will then be turned weekly with an industrial Windrow Turner while the compost matures and the mesophilic phase kicks into gear.  The mesophilic phase is where the cooler temperature microorganisms–actinomycetes, bacteria and fungi, as well as invertebrates–kick into high gear to consume remaining hard-to-break-down compounds.

Like a fine wine or cheese, this extra time helps us achieve the optimum chemistry and mix of organisms in our compost.

While piles are turned, moisture content and temperature is monitored.   Piles are covered with breathable tarps in high rain events or water added during extremely dry periods.  ALL of this to maintain ideal moisture and oxygen levels.

Step 6: Screening #2

Once ideal temperature and moisture levels are achieved, the Compost is put through an industrial screener with a 3/8” screen.

More of  the “overs” (see description above) are removed at this stage. Screened wood chips and other organic materials are recycled back into future batches.

Step 7: Quality Control

We go above and beyond with our quality control to ensure that our compost is fully mature and safe to use.

High carbon wood ash is mixed into all new batches at a ratio of about 3% by volume. This is the optimum level that acts as a safeguard against herbicides without affecting the pH of the compost.

Samples of each batch are lab tested for maturity, pH, nutrient concentrations, phytotoxicity, pathogens and heavy metal concentrations.

We run growth trials in our greenhouse of samples from every 100 cubic-yard batch to confirm optimal growth potential.

Read about the best practices we are following to slow the spread of jumping worms on our jumping worms page.