Why bother composting? Well, other than that whole virtuous “waste not, want not” ethic, there’s an entirely practical consideration.
Way back when I was probably the only Art major in history to take Soil Science as an elective, the professor announced that Muck is the most productive type of soil, provided it’s properly drained. The following lecture, he got into that whole NPK thing and into the weeds of how many pounds or 5-10-5 or 10-10-10 it would take to improve soil. Dumb me. I raised my hand and asked, “What about compost?”
“That’s Muck,” he snarled. I was so taken aback I didn’t ask the obvious question, “Didn’t you just tell us that’s the best soil?”
Now from the NPK standpoint compost ain’t squat. (That’s Nitrogen, Phosphorus & Potassium, in case you were wondering. Why is Potassium “K?” Greek to me. Okay, Latin, Kallium.) Compost freights in at barely 1-1-1. So what’s the big deal about it? Why is compost (AKA Muck) considered the best soil?
What it lacks in NPK it more than makes up for in a host of ways. Humic Acid, for one, helps break down soil nutrients into forms that are easier for plants to absorb. It also gives a home to mycorrhizal fungi, which interpenetrate plant roots. In exchange for getting a cut of the nutrients the plants produce via photosynthesis, the fungi act as an auxiliary root system, sharing what they absorb from the soil. Win-win, I say. Chemical fertilizers are too harsh for the beneficial fungi, killing them off. I suspect this is why plants need greater and greater quantities of that convenient NPK-in-a-bag stuff each year, once you start down the chemical path. The humus, or fibrous bits, absorbs water, aiding in water retention, plus all the micronutrients from plants past are there to nourish plants present. It’s also in bigger chunks than soil particles, which helps aerate the soil and make it easier for plant roots to penetrate.
Well, now that you have something to put compost in, we might as well deal with the process of making the stuff. So, how, lacking a herd of muck-producing livestock, do you make your own Muck?
Mother Nature recycles. Anything that dies, is excreted, shed, or sloughs off becomes food to those at the bottom of the food chain: microbes and fungi. These organisms digest the dead stuff, breaking it down into its component nutrients. Plants can then absorb those nutrients through their roots, and in turn we absorb them through the villi in our small intestines, after the appropriate slicing, dicing, and application of heat.
Looked at another way, those microbes and fungi are the prep cooks for the Vegetable Kingdom. So how do you keep the help happy and productive?
They’re pretty easy to please, actually. They need three things: food, water, and air. Pretty much like us, but not such picky eaters.
You don’t need a bin to make compost: it’s just a way of keeping it in one place and controlling the shape of the pile. I’ve read that 4’X4’ is really the minimum but found that our 3’X3’ design works well. In a pinch you can use a hoop made of chicken wire or other fencing, or if you have a secluded spot in your yard, dispense with walls entirely. If you do, though, your heap will work slower, since it will tend to form into a cone shape and the sloping edges won’t heat up enough to rot quickly. Also, animals will be able to dig around in it, scattering it all over. Messy. So un-suburban.
There are some things that you should not put in a compost heap, however, and this is not so much for the benefit of the bacteria as for the benefit of your sanity. Never put anything containing animal products, with the exception of herbivore poop, into your compost heap. You will have guests…guests that you really don’t want [coughratscough] So, bread crusts, yes. Bread crusts with mayonnaise, no. (Peanut butter will draw varmints, as well.) Rinsed eggshells, yes. Eggs, no. Rabbit, horse, poultry, or cow poop, yes. Dog and cat poop, no. Dog hair, yes. It contains nitrogen. We’ve been known to empty our vacuum cleaner bags into the compost heap. But I digress…Your poop, hell no. Goop from your fish filter, yes. Dead goldfish, no. See the pattern?
You don’t need animal waste to make a compost heap. You do need a carbon:nitrogen ratio of 35:1. So what’s carbon?
Any dried plant matter, pretty much. Dead leaves, straw, sawdust.
Green plant matter and poop, basically.
So what do I do with this stuff?
You make a big, fat lasagna. Unlike regular lasagna, you don’t have to make it all at once, and you never, ever use cheese. (See above.)
Start with a layer of coarse material. Corn harvest is a great time to start a new pile. Cut the stalks to the size of your bin. Put down a layer running right to left, then another layer at a 90° angle to the first (front to back in the bin or pile) alternate 3 or 4 layers, then drop in your first nitrogen layer: kitchen waste, fresh-pulled weeds, or fresh grass clippings. An inch or two will do. The sturdy stalks on the bottom will create an air pocket that helps aerate the heap.
Now scatter some dirt on top (if you’re using fresh-pulled weeds, you can skip this step). Top with something dry and brown, like straw or leaves. If you are using leaves, run them over with the lawnmower to cut them into bits. Otherwise, they will pack down into an impenetrable layer that will take years to break down. Layers can be 3” (leaves) to 6” (grass clippings) thick. Grass clippings are in a league of their own. They are high in nitrogen, so they break down fast. If you live in suburbia, (and if you’re reading this blog, that’s likely) grass clippings will be your most reliable and abundant compost ingredient. The only thing to watch for with grass clippings is that if you make a layer of them too thick (more than, say 6 inches) they will tend to clump up, starving the bacteria of air, so if you’ve hit the grass clipping jackpot, toss in a layer of dirt and something with a little structure, like straw, every 6 inches.
Sawdust is a special case. It contains lignin, a form of carbon that it much harder to break down than, say, straw, so if you’re using sawdust, the max is ½ to 1 inch per layer.
Lather, rinse repeat. Eventually your bin will be full. Then what?
You may need to water the pile occasionally. Check it by sticking your hand carefully a few inches deep into the center of the top. Why carefully? Because if your microbes are happy, they will be cookin’. The center of the pile should reach 150°. You may see steam rising off it on chilly mornings. You’ll also watch it get shorter, day by day, as the contents of the pile break down. It’s okay to keep adding to the pile while this happens.
If it doesn’t heat up, it’s most likely too dry. Just add water. However, it should be moist, not soggy. If it’s been raining a lot and the compost is not heating up, well, that means too much water, not enough air. You may have to poke holes in it at 6 inch intervals by ramming a stick down into the heap. The third possible cause for a sluggish heap is too much carbon, not enough nitrogen. Mixing in grass clippings will solve that, but in an emergency, a tablespoon of ammonia mixed into a quart of water, then watered in, will perk things up. (I know…nasty chemicals in your beautiful organic compost heap, tsk, tsk. I’ve never had to resort to the ammonia trick, nor to the nice, natural, organic alternative that you can probably get away with in the country, but not in suburbia…think about it: what’s liquid, high in nitrogen, and produced by animals…need another hint? It’s yellow.)
It’s not necessary to cover the heap with black plastic to make the sun heat it up, The bacteria make the heat. However, if it’s winter and you’re in a very cold climate, you could cover the heap to protect it from the cold. If you do choose to cover the heap, cut some slits in the top to allow air and water to get in.
After about 6 weeks the pile will cool. The material in the center of the pile will have decomposed and matted down to the point where the bacteria are starved for air. Time to turn it. (That’s why we build our bins in pairs.) As you move material from one bin to the other with a spading fork or pitchfork, (A shovel will be useless with the tangled mass of half-rotted weeds and stems.) try to put material from the outside of the heap to the middle and the stuff from the middle toward the edges, so that you’re turning the heap inside out as well as upside down. At this time, you can add additional layers of grass clippings or chopped leaf/grass mix, which will increase the nitrogen level and help break down the remaining clumps and stems. This, BTW, is a great upper body workout that will save you a trip to the gym.
While the second bin is cooking, you’re probably filling up the first with a new collection of garden refuse. After the second round of decomposition, the first batch of compost will be mostly decomposed. Move your brand new garden soil to the garden, mixing any not-fully-rotted material in with the new batch as you turn it into the second bin.
And the Circle continues.
Links: (Hat tip to Town & Country Gardening)
And check out the book Compost! in the Suburbutopia Toolshed.