Way to Compost 3: The 3 Bin System

As an intern on an organic farm, I used to compost a lot of raw farm material. The farm was certified biodynamic, which meant that as much as possible, we strived to be a closed system—a farm “organism.” Very few inputs came in (coffee and chocolate were the much needed and celebrated exceptions), and no outputs went “out.” We had to take care of our own outputs, if you catch my meaning.

Imagine the farm as an organism. Humans and animals eat plants and grasses, burn energy, and leave behind various forms of waste. Trees take in carbon dioxide, burn sugars, and give off oxygen. Worms eat decaying material, pass it through their marvelous guts, and leave humus as waste. On the farm, weeds, grass clippings, used water, sheep wool, chickens that did not run for cover from the hawk, leftover milk, garbage, manure, and yes, even our own “humanure” were all waste streams that needed to be transformed into usable energy once again. Constant compost!

In order to keep all of these outputs organized for the composting process, we used the 3-bin system. This could be anything divided into three separate sections, often by moveable pieces of lumber such as pallets or boards. Strawbales are also a good material for building the bins. Once strawbales start to decay, you can just add them to the compost.

The bins were at least 3 cubic feet, and needed enough space in the front for a person to use a shovel or front loader to turn the pile form one bin to another. Placing bins in the shade is a good idea, and making sure there is good drainage is also important. If it rains, compost piles tend to leach nutrients. Building the bins right onto the soil is a good solution to this problem, as long as your soil drains well. Covering the pile with straw, a tarp, or leaves also helps to keep the pile from becoming too saturated.

When compost day came, (usually every two weeks or so) all of the manure, kitchen scraps, and brown material I had stored in the first of the three bins was made into a compost pile in the middle. Here’s how I made it:

The first layer was about an inch of chopped sticks and twigs from my pile of “brown” stuff in the first bay. These provided an air pocket on the bottom of the pile for good air circulation. When the pile built heat over the next day or two, convection currents would draw air from the bottom of the pile up through the top. This provided hard working microorganisms with oxygen and kept the pile smelling pretty fresh.

After this first layer, (the crust, if you will) I filled it with a compost cake. First, brown stuff, then greens from the kitchen can or the manure piles. Next, water it if it seemed too dry. Compost piles should have the moisture content of a wrung out sponge. Then brown, green, water and so on, until I had layered all of the stored up piles of “waste” into a fabulous monster of a seven layer compost cake. I would frost the pile with leaves, strawbale flakes, or sometimes a tarp if it was going to rain a lot. This top layer shed moisture and kept off flies. It also looked very neat and tidy.

Then I let the pile sit for a couple of weeks to bake. The temperature of the pile peaked the first week at around 150 F, then it slowly declined. At the end of the second week, I peeled off the outer layer, prepared a bottom layer of twigs and sticks in the 3rd bin, and turned the pile into it. To make sure that material that may have been left on the outside of the first pile had time in the middle, I shoveled vertical “slices” of the compost cake, from right to left, into horizontal layers from bottom to top. Farmers with front loaders have their own methods for making sure all the material gets a chance to be in the hot seat. This was my from scratch, by hand method.

By the time I turned the pile from the 2nd to the 3rd bin, the first bin was already filling up with more brown stuff, the cows and chickens were piling up more manure, we had eaten and left behind plenty of kitchen scraps to use again, and the middle bay was waiting to be filled. Waste streams do not take vacations.

The 3rd bay got two more weeks to be worked on by bacteria, fungus, and other microorganisms in the pile. It fermented while the new compost cake in the second bay cooked. When it smelled done, earthy and mushroomy and energizing, I moved it into the garden beds or under some trees until we are ready to use it. During the winter, the bays can store browns and greens until the earth warms up and compost organisms are in abundance and active again.

This 3 bin system works beautifully if you have a front loader to turn the compost–or if you want to skip your gym membership and do lots of shoveling instead. It works well for those who have a lot of material they need compost fairly quickly on a regular basis (community gardens) and have time to make, turn, and use several piles a year—or for those who have a very willing and enthusiastic intern. 

Stay tuned for more ways to compost as the winter turns a celestial corner to spring.

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