Good Compost

Before coming here, C and K each independently experimented with indoor compost bins in separate apartments. These were ventilated plastic tubs that housed colonies of red worms that ate kitchen scraps. Even though both ate similar vegetarian diets and got their worms from the same source they ended up with quite different results. C's bin slowly accumulated a dark, moist but not wet, odorless substance that bore close resemblance to healthy soil. K's bin, tended with roommate A, filled with a soggy, foul-smelling, black muck that attracted flies like a sewer. Even a pair of naifs like K and A could tell that this wasn't good stuff, so they gave it to their local compost expert who made her best efforts to remediate it.

This bad news is actually good news because it means that as far as decomposed organic matter is concerned, it is easy to tell fair from foul. Bad “compost” isn't really compost at all. The decomposition of organic matter isn't rocket science, but it is a process with several specific stages that is something of an art to manage.

The practice of using compost to enrich soil is at least as old as ancient Rome. Since the Romans didn't have microscopes we assume that they didn't have a clue about what makes compost good stuff. We suspect that most people still don't---we sure didn't before coming here.

It is true, as you have heard, that good compost is chock full of nutrients beneficial to plant health. It is also true that these nutrients originate in pre-compost organic matter that is changed into a different form through the process of decomposition. What many people seem to misunderstand is how this decomposition is carried out: our “worm bins” had a lot more living in them than just worms.

Please see our previous post on the soil food web (link) and ponder how many of these critters you can actually see with your naked eye. These invisible guys are essential to the process of decomposition, and, like the stuff they produce, are not created equal. The only difference between C's bin and that of K and A was the bore of the drill bit used to aerate the bins. The air holes in C's were large enough, whereas K's were too small. Not enough air got in K's bin and the wrong kind of microorganisms bred. They were plenty busy with the organic material, but the anaerobic nature of the process contributed to growth of “bad guys,” the kind that produce disease and alcohol.

While indoor worm bins (“vermicomposting”) are growing in popularity most people make compost in an outdoor pile like is done here on the farm, so we'll continue our discussion of making good compost with that process in mind.

First you start with organic matter. Most things from plants are good: leaves, grass clippings, etc. Kitchen scraps are fine, but no meats, oils, fats, or products treated with preservatives. Animal manure, while fecund, is probably too risky. Cattle manure in particular used to be a must-have compost ingredient but industrial agricultural practices have led to the spread of e. coli, which gestates in the digestive tract and can leave traces in droppings, not too mention drugs and hormones. Don't use it unless you know the animal and its diet as if it were your own.

Proportion is important. Organic matter can roughly be divided into “green” and “brown” types. Green matter is composed of simple sugars that bacteria love whereas brown matter has more complex carbohydrates that are better food for fungi. Green turns into nitrogen while brown becomes carbon. The ideal C:N ratio depends on what you want to grow.

Next, add time, moisture, heat, and air. Nature will do most of this for you, though she may need a little artful assistance to make the process go smoothly. We've already explained the need for air. Since we're no longer talking about enclosed tubs (though some people do keep those outdoors) you just need to turn the pile over once in a while.

Turning the pile also makes sure that the heat is evenly distributed. The temperature will vary at different stages of the process (there are three, each dominated by a different type of microbe) but shouldn't go over 150F---that will kill the good life. How's it get so hot? Even though we're talking outdoors here, it's not the sun. Heat is a byproduct of the process of decomposition itself: trillions upon trillions of microbes getting sweaty.

The pile should be neither really wet or dry. If you live in a dry area you may need to add water, if you live in an area with lots of rain you may need to put a tarp on top. Just a little bit of moisture is all you need.

Allow for enough time under the right conditions and you should end up with good compost.

Or, if you're lazy, you could just buy the stuff. If you do, get a list of ingredients and make sure they're organic. You don't want any remnants of synthetic chemicals that will endanger the soil food web.