We talk a lot about compost, what it does for plants, water retention and soil tilth, but what we really mean is that it replenishes nutrients we’ve taken from the soil.

We grow glorious flowering plants, and deadhead spent flowers to prevent the plant’s putting energy into making seeds. Those dead flowers go into the compost to restore the soil. So do all spent plants, prunings and plant parts.

When we grow vegetable gardens, we obviously can’t give those vegetables back to compost because we’ve eaten them. We can and do put kitchen waste, eggshells, herbicide-free lawn clippings, shredded paper and fallen leaves into the compost pile, and wherever we can find “clean” organic matter, we may add that.

When we can obtain animal manure that’s free of pesticides and worm medications, we may put in a layer of that, too, to increase microbe activity in decomposition of the compost pile. It’s not necessary, however.

If you have access to rabbit manure, that’s very good, and should not be too “hot” even for immediate use on your plants, or it can be used in compost. Chicken manure is fine for composting, but too hot for immediate use. Hot manures are those fresh high-nitrate manures that spur microbe activity to such a level that they burn up nutrients and damage plant root tissues.

Never use cat or dog manures in compost, for they may be carrying parasite worms or eggs that will contaminate your compost. Cats may carry toxoplasmosis that can be extremely dangerous, especially for pregnant women.

Horse and llama manures should be aged at least 90 days before being added to the compost pile, I think. Both animals are regularly treated for worms, and one veterinarian I spoke with said he thought the worm medication lost its effectiveness in two to three months. I fear that fresh vermifuge would also have a killing effect on micro-organisms in a working compost pile.

One must be cautious about using any large animal manure because of the residual effect of modern herbicides. If animals have been grazing on fields sprayed with herbicides containing Clopyralid, Aminopyralid or Picloram, it passes harmlessly through animals, we’re told, but these chemicals are excreted as solid herbicides. The contaminated manure keeps its broadleaf plant killing effectiveness for more than three years of composting.

Similarly, plant material exposed to those herbicides retain that toxicity through composting for years.

For a compost pile, you’re supposed to “layer” browns and greens, 25 times more browns (carbons) than greens (nitrogenous or animal wastes), then keep the pile moistened like a damp sponge, and make sure it has adequate air, top to bottom. To make sure of the latter, many people turn their compost piles regularly, or use a tool that, once thrust into the pile, extends “wings” when you start to withdraw the tool, exposing a fair amount of the pile to oxygen. Depending on the size of the pile, it may take several pokes to thoroughly aerate it.

Nitrogenous materials, or “greens,” include grass clippings, alfalfa meal, blood meal, poultry and other animal manures. Browns are brown or yellow, dry, coarse and bulky organic matter. Never use meat, bones, grease, dairy, peony clippings, walnut leaves or blight-afflicted plants in your compost.

All materials will decompose faster if they’re mechanically chipped or shredded.

Lawnmowers exert sufficient vacuum power to pick up and shred fallen leaves, and that also prevents their matting and barring water when they’re used as mulch. If they’re used in compost, they decay faster than whole leaves.

Many folks use commercial barrel-like composters or just three or four pallets wired together. A three-pallet setup is easily accessed for turning.

Another method is sheet composting, laying your organic matter on the soil or in holes or trenches, and then tilling it in or covering it with soil.

Some compost piles heat up quickly, and may become more than uncomfortably hot. If set up next to a wooden fence, for instance, it’s embarrassing and dangerous when the pile catches the fence on fire.

Compost piles set up in less than ideal layers will eventually decompose into good compost, but are regarded as “cold compost.” Proper layers, moistness and air just hasten the process, creating “hot compost,” but don’t depend on getting “black gold” compost in 14 days. In spite of the advertising, I haven’t met anyone who’s succeeded to that extent with any equipment.

Compost is completed when you can no longer identify pieces in it. It can be used as mulch, or spread on garden beds or around shrubs and trees to a depth of about an inch.

It increases microbial activity in the soil food web when compost tea is thoroughly aerated and applied to soil. When I’ve applied it to nearly compacted soil, it turns into light, fluffy soil within days. Some folks also use compost tea as a foliar feed to restore or maintain good health of plants.

Researchers at Laval University in Canada found that “ramial wood chips” worked wonders in soil conditioning when laid atop soil. The branches already had the right ratio of green (cambium layer) to brown (heartwood), and contained their own moisture.

Dead trees or shrubs lack the green layer, so they don’t work as well.

Most of us build “cold compost” piles, adding a little organic matter at a time.

That works, too. Rot happens in its own time. And if we move across town, the first thing gardeners move is their compost pile. That’s how valuable this black gold is.

Margaret Lauterbach: melauter@earthlink.net or write to Gardening, The Idaho Statesman, P.O. Box 40, Boise, ID 83707