Many people often ask us about the process of composting and how exactly their food or yard debris becomes nutrient-rich soil. One major question is, “What happens to weeds or food pathogens?” Well, we wanted to answer those questions and help explain a bit about the commercial composting process. We hope this helps.
Feedstock is basically anything that goes into the composting process. For us it’s mostly yard debris from Hood River and The Dalles transfer stations, food scraps from our food compost program, orchard and land clearings, plus food waste from industrial groups like Oregon Cherry Growers, and Turtle Island Foods. The incoming feedstock is stored on our compost pad, which is designed to collect any and all rainwater that comes into contact with feedstock material.
We grind all incoming woody material into 3″ pieces. This allows the material to breakdown more easily and let air pass through the piles, so they can breathe (a.k.a aerobic conditions).
Step 3: Create Recipe and Blend
Composting occurs due to microbes eating organic material and thereby breaking it down into soil. These microbes thrive in an ideal environment of 55% moisture, good airflow, and a 30:1 Carbon to Nitrogen ratio (for Carbon to Nitrogen think brown (wood, leaves, etc…) to green (food, grass, etc…). Knowing the Carbon to Nitrogen ratios of our incoming feedstock we blend them to create the ideal microbial environment. We mix the material into large trapezoidal piles called windrows.
Step 4: Monitor and Turn
We closely monitor the windrows for the ideal conditions (temperature, moisture, oxygen, porosity). When these conditions exist, microbes flourish and heat the piles up to 140-170 degrees F. This is important, because the high temperature kills off weed seeds and other potential pathogens (like fertilizer put into grass clippings). According to National Organic Standards and DEQ we maintain a minimum of 131 degrees F for 15 consecutive days and turn the windrows five times in the same period. This ensures a uniformly hot and mixed pile.
Step 5: Aeration + Curing
Once the windrows have been through the previous stage, they have passed the “pathogen reduction phase.” The microbes are still alive, kicking, and breaking down material, so it’s not ready for your garden yet. Initially, we lay compost over aeration plenums, which introduce oxygen to the piles on set timers. After an aeration phase, compost is moved off-pad to a curing pad. Compost at this stage can cure from one month to two years. In many cases it’s like wine, the older the better (but it also depends on the use, sometimes immature compost is preferable too). This phase is important for soil maturity, stability, water retention, respiration and nutrient content.
Step 6: Screening
At this point the soil has cured and is sufficiently mature. We run the material through a screener to create a finished compost worthy of planting by the handfull. Screening separates larger pieces from the fine soil and can remove any contaminants (i.e. plastic) not picked out during the composting process.
At last the compost is ready for use in the farm, field, garden, or yard!