What the heck is “Active Batch Composting” anyway? You’re about to find out, but first let’s look at another term: Cold composting.
Cold composting, though the name is a bit of a misnomer, is what most gardeners do. We have a compost bin or pile, and over time we add our kitchen scraps and garden waste, some leaves and shredded office paper, tissues, paper towels, etc. We water it and wait. The temperature may climb to 100-120°F but that’s about it. We can turn the pile to speed things up, and in 3 months to 2 years, we have finished compost.
Active batch thermal composting is when we build a complete pile all at once with a specific ratio of materials to achieve a steaming hot pile of microbial-rich finished compost that has reached temperatures upwards of 160°F during the process.
That’s what we did this week. Here’s how:
Last week we cut down our winter cover crops and left them in the sun to dry down for a few days. Next we shredded the pile of dry biomass from last year’s shrub pruning:
The dry biomass fulfills the carbon portion of our formula (that’s your brown material), the green cover crops are the nitrogen part of the equation. In addition to that, we added some high-nitrogen ingredients of chicken manure and kitchen scraps.
Next we combined all ingredients in layers into an empty compost bin. It’s important to water the entire pile as you add layers so that each ingredient becomes thoroughly soaked.
Next we wait…
The pile should begin climbing in temperature almost immediately, but it can take between 18 to 24 hours for it to reach peak temperature. As I write this, it’s been over 24 hours and here’s our pile:
We were a little shy on high-nitrogen and nitrogen materials, which accounts for temps below 160°F, but it’s not too shabby if I do say so myself.
When the temperature begins to drop, we’ll turn the pile and water it again as we turn each layer. Then it will be turned one more time before being left to break down for the next couple of months.
To find Dr. Elaine (Soil FoodWeb) Ingham’s specific ratios and a starter formula for building your own active batch thermal compost pile, check out my new book Gardening for Geeks.