Monday, September 6, 2010

Composting 101

Today brought us our first batch of compost! While Margo and Alten built a new pile, I broke up the finished one and sifted the cured compost from the un-decomposed material. It looks great, smells great, and marks the beginning of our garden's trip toward soil rejuvenation. Hurrah!
In honor of the occasion I am reprinting here the first of three compost-related posts I wrote for the Golden Rule Garden blog in May of last year...

Here I sit, in the shade, sipping cold kombucha in the midst of our first 100° F days of the year. What topic could be hotter than compost? Or more appropriate, given that it is Spring and we have an abundance of weeds, cover crops (which we refer to instead as "compost crops"), and all the dry, stalk-y, crunchy mature material we saved from last year.
Michele, of the Rabbit Wrangler Ranch in Idaho, posted some questions after reading my admittedly vague reference to our composting in the Happy Spring Equinox post. Hopefully this will answer your questions and bring up a lot more.
I often feel like most of my experientially-oriented posts should start with a disclaimer, so here's this one: there are many ways to compost, many books written on the topic, and many, many products sold to help you compost. This is how we do it here, and how it is taught in Grow Biointensive agriculture through Ecology Action's courses.
The recipe is fairly simple: 4 parts mature material, 4 parts immature material, one part soil. Add water. Sounds easy, right? It is. And the details aren't even very devilish.
Mature material, popularly referred to as "dry matter", consists technically of any plant matter that has achieved full maturity. The easiest example is straw, which can come from rice, wheat, rye, barley, oats, and so forth. Also included are corn stalks, quinoa stalks, sunflower stalks, amaranth stalks... You get the picture. Essentially anything that is tough and crunchy. Tree leaves that fall of their own accord count. Burnt bacon doesn't.
Immature material, popularly referred to as "green matter", is basically anything that has not gone to maturity. Slug-eaten lettuce, grass clippings, most kitchen waste, weeds (which you hopefully got before they went to seed, because then they'd be mature material with a dark side), and anything else you pulled out before it completed its life cycle.
The reason for the revised terminology is that the common terms are deceptive. Grass clippings that have been sitting on the lawn for a week can certainly be dry and brown. But that does not change their composition, except that there is less water in them. And it's all about the composition.
I will oversimplify to illustrate my point: for our composting purposes, anything you put in your pile is made up of carbon and nitrogen in varying ratios, and the carbon involved varies in its density. The mature material we use is relatively higher in carbon than the immature, and the carbon is denser. Because of that fact the organic matter from composted mature material will last much longer in the soil, which is what we want. But if you build a pile only of mature material it will take years to break down completely.
The microbes that will decompose your pile want appreciable amounts of both carbon and nitrogen, which is where the immature material comes in. Though its carbon is less helpful to us in the long run, immature material is relatively higher than mature material in nitrogen, and its presence in the pile will help the microbes do their job and give you lots of nice, long lasting compost (human-encouraged organic matter), which in turn makes your soil system healthier which makes your plants more productive and pleasing to the eye, and eventually culminates in world peace.
Soil is the last ingredient, and we add it in small quantities for a couple of reasons. It's true that adding soil inoculates the pile with helpful microbes (which would have happened eventually anyway), but more importantly it helps the pile maintain moisture and moderate its temperature. This may be less necessary in a cooler, moister climate than ours, but is vital here.
Now you know the ingredients, so here's how it goes together: Choose a spot to build your pile, preferably in direct contact with soil, and possibly on a garden bed you can spare. The liquid that leaches out will do great things for the soil underneath, and direct contact will also aid microbes coming and going through your pile. It should be a minimum of 3x3', which will help maintain the core temperature and moisture of your pile. It can be bigger if you like, but not smaller.
Stick a fork in the soil to loosen it where the pile will go, then lay down a few inches of rough mature material. This is a different category of mature, things that won't break down easily. Like tree branches. The point is to allow air to enter the pile and excess moisture to leave. It also creates a definable bottom to the pile.
Now you start building, adding a layer of mature, a layer of immature, and a layer of soil. We use 5 gallon buckets (not sustainable, no, but plentiful, free in any quantity, and standard in size for measuring). One layer for us is two buckets of mature, two buckets of immature, one-half bucket of soil.
Oh- and we build them as square as possible. This makes the most efficient use of space and materials. Plus they are aesthetically pleasing...
At this point, having not answered more than one of Michele's questions, I am going to end this post. The next, Composting 102, covers a little bit of the what's, why's, do's and don'ts of the process, hopefully answering some of the questions that this post generated.

1 comment:

  1. interesting post and accounted for a really engaging read. Thanks for putting in the time and effort to post this and share it with all of here. Admire your work.