Wednesday, September 15, 2010


Compost, in all of it's biological complexity and symbiosis, is an extremely simple backyard project. The problem with compost is that there are so many blogs (like this one?) and webpages touting it's beauty and simplicity that it can be a bit depressing when your compost pile goes horribly wrong. Molding piles of wet food scraps surrounded by swarming fruit flies is not what you had in mind.

The Basics of (Hot) Composting:

Compost is the process of breaking down organic matter so that the nutrients contained within become water soluble and accessible for the plants. There's other nice side effects too. Compost can get hot enough to kill pathogens and weed seeds. When added to the soil, it increases the number of beneficial microbes and mychorriza (fungus that lives on roots), aids in water retention and serves as a mulch. The action of compost isn't due to any one thing--many different bacteria, fungi, and even little critters get in on the action. Looked at as a whole, it can summarized as an exothermic (it gives off heat), aerobic (requires oxygen) reaction, that takes in carbon and a little bit of nitrogen and pumps out methane and leaves behind something you can spread over your garden.

The Problem with Composting Advice:

Without a doubt, the most efficient compost pile is constructed all at once. For obvious reasons, this is called batch composting and has a distinct industrial flavor. You gather at least a cubic yard of materials containing the correct ratio of carbon to nitrogen, plop your enormous pile in your backyard, turn it every few days and in short order your compost will be done. This begs some obvious questions:
  • Who produces a cubic yard of organic waste all at once, and then nothing for the next 3 months?
  • Who produces organic waste in the correct ratio of carbon to nitrogen?
You might, actually, if you're composting scraps from a big vegetable garden and can compensate your extra nitrogen with leaf matter, but most of us are looking for away to keep our kitchen scraps from going in landfill.

The Problem with Kitchen Scrap Bins:

The question then becomes "Whats the best way to kind of batch compost, adding materials from your kitchen and garden as you go?" We'll get there soon, but for further inspiration lets look at likely downfalls in a backyard bin. You cannot just start throwing your food scraps in a pile in the backyard. (I promise, I tried, the fruit flies were bad but the rats were much worse.) Pitfalls can be broken down into three categories:
  • Too wet -- compost piles need water, but anything leaving your kitchen is likely to contain way too much water. This has the effect of smothering your compost pile (which remember, needs oxygen!) and making it anaerobic. You can smell anaerobic. Not good.
  • Too green -- likewise compost piles need nitrogen, but anything leaving your kitchen is likely to contain way too much nitrogen. This produces ammonia. You can smell ammonia. Not good.
  • Too small -- Your too wet, too green compost pile hasn't been breaking down the way you want, but it has been breaking down (maybe by mold, maybe those rats are carrying pieces away). Your compost pile will never actually grow in size. You might think this is ok, until you go to harvest your compost and take a whiff of those anaerobic byproducts mingling with ammonia. Being exothermic, proper composting action releases heat which then speeds up it's own reaction. This is an example of a positive feedback. (Actually, fire is much the same way. Compost is just a little more mellow.) Too make this efficient, your pile needs to be insulated. What better insulation is there for compost than compost? Moral of the story: if your pile is big, it will insulate itself, trap the heat in, and make the reaction go even faster.
  • The Element of Time -- Time, like water and nitrogen, is an element in compost. It can also present compost management problems in two ways. First, some food scraps compost much faster than others. The coconut shells that have recently found there way into my bin could be there for years. Short of some time consuming process of chopping everything up, there's no way around this. Secondly, if you're continuously adding material, some material will have been in the bin much longer than others at harvest time.
Dave's New (and untested) Deep Litter Method:

Hopefully, over several posts, I will track the progress of a method of composting that I've converged upon with several iterations. The idea is to view the capacity of your compost bin not by the size of the bin but by the amount of carbon in it. If you follow this paradigm, an empty compost bin has no capacity to compost, whereas a bin nearly full of leaf litter has tons. This is very much analogous to bedding for pets or kitty litter. A little box with no kitty litter in it doesn't have much capacity to keep your house from getting smelly.

That's pretty much all there is to my method, I'm starting with a full bin rather than an empty one. I'm calling it a deep litter method after the deep litter method used in raising animals. How will I add to a bin that starts almost full? To paraphrase Abahram Lincoln, the brave microbes which live there will compost far faster than our poor power to add or detract. I'll bet dollars to donuts that my bin shrinks rather than expands, no matter how many kitchen scraps I add. Early returns seem good. I started the bin 4 days ago and the top of the bin (where I've added food scraps) is rockin' at 145 degrees while the other parts of the bin seem to be hanging out around 105 degrees.

I'll delve into more detail concerning the construction and management of the bin later, as well as discuss how this method deals with some of the problems listed above. I'll also report on some results. Unfortunately, there's more to life than backyard agrarianism. Back to real life...