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 means 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 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. We composted all the time!

In order to keep all of these outputs organized for the composting process, we used the three 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, 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 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.

Over the span of a couple of weeks, I would gather dry materials such as old plants, leaves, sticks, straw, and hay and store them in the first bin. We kept kitchen scraps over that two week span in a garbage can with a lid nearby. I preferred to store it in one place until I was ready to make a pile, rather than throwing it on the pile daily. This way, I make sure these smellier scraps are buried in the middle of the pile and don’t attract critters. We also piled manure from chickens and the dairy cow in neat piles in their stalls until we were ready to build a bigger pile. When compost day came, all of the manure, kitchen scraps, and brown material was made into a compost pile in the middle bin. Here’s how I made it.

The first layer was about an inch of chopped sticks and twigs on the bottom of the middle bay from my pile of “brown” stuff in the first bay. These provide an air pocket on the bottom of the pile for good air circulation. When the pile heats up, convection currents draw air from the bottom of the pile up through the top, providing the hard working microorganisms with oxygen and keeping the pile smelling good. After this first layer, I make compost cake. First, more brown stuff, then greens from the kitchen can or the manure piles. Then water it if it seems 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.” I would frost the pile with leaves, flakes of a strawbale, 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. The temperature of the pile often peaks the first week at around 150 F, then it slowly declines. At the end of the second week, I take off the outer layer, prepare a bottom layer of twigs and sticks in the 3rd bin, and turn the pile into the 3rd bin. I shovel vertical “slices” of the compost pile, from the right side to the left side, into horizontal layers from bottom to top. This way, all material that may have been towards the outside of the pile get turned into the middle.Of course, you do not need to be this precise. Farmers who use front loaders have their own methods for making sure all the material gets a chance to be in the hot seat.

By the time I turn the pile from the 2nd to the 3rd bin, the first bin is filling up with more brown stuff, the cows and chickens are piling up more manure, we have eaten and left behind plenty of kitchen scraps and the middle bay is about ready to be filled again. Waste streams do not take vacations.

The 3rd bay gets two more weeks to be worked on by the bacteria, fungus, and other microorganisms in the pile. Then it is ready to move into the garden beds or be stored under some trees until we are ready to use it. The busiest times for this kind of composting are the summer and fall. During the winter, the bays can store browns and greens until the earth warms up and compost organisms are in abundance again to help us break them down into humus. 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 and have time to devote to making several piles a year—or for those who have a very willing and enthusiastic intern.

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