How to Compost and How it Works

You could live a long time on bacon, doughnuts, and vitamin pills, but nobody would ever mistake you for a healthy person. Yet many gardeners feed their gardens a similar diet—chemical fertilizer and little else. While such a diet can produce remarkable short-term growth, it can seriously stress your plants. Fertilizers set up a rich/poor nutrition cycle and, like humans eating junk food, a garden's health ultimately suffers. To help plants grow steadily and fight off pests and diseases, you must feed the soil. Think of compost as a healthy food for your garden.  

Step by Step Composting

1. Contain it.

You can just pile things on the ground, but a wood, wire, or plastic bin encloses enough material to get a pile cooking. In composting, as in nuclear fission, a critical mass is required to generate heat. The ideal shape and size for a compost pile is a cube about 4 feet per side. anything less than 3 feet will never really get going. Dark containers designed specifically for composting retain solar heat and also allow daily turning, which hastens the breakdown of materials.

2. Prepare it.

after you've gathered your compost materials, cut or break them into pieces—the smaller the better. Chopping up compost materials makes it easier for bacteria to get in and do their work. Hardcore gardeners often keep materials in "holding" piles until they can be chopped, chipped, or shredded, and a chipper/shredder can be very helpful indeed. If you can't do this by machine, try a mattock or spade. Spread the chopped materials in layers 3 to 5 inches thick.

Start with a layer of brown, then add a layer of green. atop each brown-green section, add an inch or two of manure or garden soil. This ensures plenty of microbes in the pile. Boost nutrients by adding a shovelful of wood ash, rock phosphate, lime, granite dust, blood meal, bone meal, or greensand to each completed section. If your area's climate requires it, moisten each layer of the pile as you go. Use a gentle spray.

If you make your compost in a barrel or tumbler, you can forego the layering process. Just pile the materials in, add a bit of water if necessary, then turn the tumbler to distribute the materials and get things rotting.

3. Chop it and turn it.

Let your new pile heat up for three days, then turn it. To do this efficiently, you need a mattock and a garden fork. (Most any fork will do, but a manure fork or hayfork is best.) First, chop through the layers with the mattock, pulling back after each swing so that you turn the pile inside out. Next, lift and expose the lower layers with the fork, then chop them. Or—you may find this easier—use the fork to move each chopped layer to a second compost bin, and continue to chop the rest of the layers in the first bin.

The middle of the pile will decompose faster than the outside, which will remain largely unchanged; you'll especially see this the second time you turn. To work around this "cooking-from-within" phenomenon, move the outside edges of the pile in, and vice versa. after the pile has been thoroughly mixed (and transferred, if you're using two or more bins), moisten it again if necessary. You can monitor the temperature with a compost thermometer. Leave the pile alone as the temperature rises from day to day.

When it starts to drop, it's time to turn. If you don't have a thermometer, simply turn the pile every three days, but if you can't, no harm is done—your compost will just take longer. Each turning will be easier than the last because the materials get smaller and lighter as they decompose. When your pile has stopped heating up, and the compost is pretty much all the same color and texture, your health food is ready to use.

4. Use it.

Use your compost as is or screen it. To screen fresh compost, buy a riddle (a high-sided sieve) or make your own out of hardware cloth and a frame of 2-by-4s or 2-by-6s. Shake the compost through the riddle. The larger bits that won't go through the screen will still make great mulch. Used as mulch, screened or not, compost will suppress weeds, add nutrients to the soil and help retain ground moisture. Spread compost in the garden before you till or fork the soil in preparation for planting. Screened compost is a great additive for container mixes. It supplies a full spectrum of nutrients without burning young plants' roots.

How Composting Works

Look at any thriving forest and you'll see composting in action. The complex interplay of green plants, fungi, bacteria, and other microscopic life steadily converts dead organic matter into nutrient-rich food. How do you make this work in your garden? It's simple enough: compost just happens. Make a heap of weeds, kitchen scraps, grass clippings, and other organic waste, walk away, and in 18 months you'll have dark, rich compost. But if you get involved in the process, you can reduce the time to six weeks or less.

A teaspoon of healthy garden soil provides a home for more than four billion bacteria and other microscopic beasts. Make them happy, and these little agents of change will work wonders in your soil. Just remember four keywords: brown, green, water, and air. Brown and green. all compostable materials contain both carbon and nitrogen, but the relative proportions determine whether the material is brown or green. When you think "brown," think straw, wood shavings, chips and sawdust, newsprint, stalks, stems, twigs, and the like. These carbon-rich materials provide the fuel that the bacteria and their chums need to break down the greens in your compost pile. "Green" refers to wet, nitrogen-rich materials—grass clippings, weeds, pruning, and the like—and kitchen scraps (plant material only; meat and dairy scraps attract unhelpful kinds of wildlife). Not all of this stuff is brown or green, but a lot of it is, and most people find it easier to remember colors than chemicals.

a compost pile built in fairly even layers of brown and green materials will usually decompose just fine. If your pile isn't breaking down, it probably needs more green (nitrogen-rich) materials to heat up. The cure for this is to rebuild the pile adding more green stuff, or "spike" it by adding a few handfuls of a high-nitrogen granular fertilizer between layers. Some people even add animal bedding or manure—both are rich in nitrogen. Water and air.

Decomposition takes place much faster in a moist environment. Cover your compost pile with a tarp or plastic garbage bags, and it'll probably retain enough moisture to get the pile cooking. Some compost impresarios prefer to add water to the pile, layer by layer, as they build it. Climate, weather, and the moisture in the materials themselves will influence your chances of success with either method. If you live in the desert and your potato peels look more like potato chips by the time they make it to the compost pile, water the pile as you build it.

In coastal Oregon, insufficient water may be the least of your worries. In general, your compost pile should be about as moist as a wrung-out sponge: not soaking wet, but damp throughout. If your pile refuses to heat up but you think you've added enough green stuff, the problem may be insufficient moisture—or size. If your heap gets too wet, it won't hold enough oxygen to support the aerobic bacteria that do most of the work. Excess moisture also results in unpleasant odors.

Turning the pile evens out the moisture content and introduces air, the final element of successful composting. Turn the pile every three days or so, and you'll replenish the oxygen supply for the bacteria and other friendly creatures hard at work inside. You'll be rewarded with deep, dark ready-to-use compost in six weeks, maybe less. and since this method encourages rapid decomposition, your pile will heat up to 150 degrees or more—hot enough to kill most weed seeds.