Trash Can Composting

Here's our friend Matt shredding grass and leaves in a trash can to make compost. For you suburbanites out there this may be totally unnecessary: You have a big back yard in which to construct your composting system.

But for us city folk, ingenious steps must be devised to compost in small spaces, especially to keep our kitchen scraps away from the local rats.

Garbage cans are a bit smaller than what the composting experts describe as the minimum size for an "optimum" compost pile. That would be three feet wide, three feet deep and three feet tall. But in fact compost will happen anywhere, even in a crack in the sidewalk. You can bag leaves in the fall and come back in a couple of years and even those bagged leaves will be turning into compost, the ideal amendment for our organic vegetable beds.

When a neighborhood learning center near my home--the Emergence Community Arts Collective--asked me to teach a course in composting that would result in actual compost, I proposed the trash can method. Teachers at one of the local schools employ several trash cans to turn their garden debris into compost. There's plenty written about it on the internet.

I had the arts collective procure a metal trash can (tougher for the rats to get into--I hear they are often available on Craig's List). I came by and drilled a series of drainage holes in the bottom, then more holes around the sides of the can for aeration. After watching my Power Point presentation on the hows and whys of composting, a small group of eager composters went to work in the yard, filling bags with last year's leaves and pulling as much green grass as we could find.

A good compost requires a proper balance of "green" materials, such as grass clippings, and "brown" materials, such as fallen leaves. They aren't always available exactly when you want them. Sometimes it pays to store leaves over the winter for a time when enough grass clippings become available to create the right mix. But if you poke around the neighborhood, you often will find old leaves waiting to be collected in an alley or blown into a pile against a fence. Kitchen scraps and coffee grounds from the local barista also make for good compost. Composting is a good way to recycle your newspaper or shredded personal documents as well.

The students were amazed to see how the bags of leaves they collected reduced to very little when we shredded them with our electric weed whacker in the trash can. We used the line trimmer just like a hand-held blender, plunging it into the leaves and moving it this way and that. We collected more leaves. And more leaves. And more leaves. And since we didn't have a mower, we collected the grass by hand and shredded that as well.

When it was all done, our trash can was a little more than half full, about equal parts chopped leaves and grass for a quick-acting compost. One of the students had brought some shredded paper, another had a bag of kitchen scraps. We mixed that in as well, then added a couple of large pitchers of water until our mix was just damp, about the wetness of a wrung-out sponge.

"By tomorrow, this compost will be hot," I assured the class. I knew that bacteria quickly would begin to feast on the nitrogen in the grass clippings, multiplying like crazy and raising the temperature of the heap. My students looked dubious. But this morning I visited the site. The ambient temperature is 40 degrees--just eight degrees above freezing--but inside the trash can, things are already toasty.