Compost is vegetable matter, such as grass clippings, leaves, peelings from the kitchen, sawdust, animal manure (mostly made up of digested grass), even shredded office paper, that has been allowed to decompose until it forms a crumbly black substance called humus. You can use it as a fertilizer, mulch, or soil conditioner. The greatest contribution compost makes to the garden is by adding organic matter to the soil, which makes soil easier to work and better able to hold the right amount of moisture and nutrients.
You may have heard that composting requires layering materials and containing them it a bin. While some gardeners do use elaborate methods, they aren't necessary. You can create compost by just heaping materials into a pile and letting it decompose at its own pace (this approach is called cold composting and takes about a year). You can speed up the process by keeping the compost pile slightly damp and turning it with a pitchfork or spade every week or so. This method is called hot composting because the moisture and oxygen make decay microorganisms so active that they produce heat. The temperatures in the pile can reach 160 degrees Fahrenheit (hot enough to kill weed seeds and most disease pathogens).
Feeding the Pile Decay microorganisms have to balance nutrients in their bodies just as people do. They usually can find plenty of carbon, which is abundant in leaves, straw, sawdust, and shredded paper. They may run short on nitrogen. You can improve the balance, and speed up decomposition, by adding materials higher in nitrogen, such as fresh grass clippings, fresh manure, alfalfa hay, and vegetable scraps. Or you can sprinkle the pile with bloodmeal, which you can buy at garden centers. Avoid adding grease, meat scraps, and bones (these break down slowly and may attract animal pests). Large leaves, twigs, and branches also break down very slowly unless you shred them first. Unless you keep your compost pile very hot (and most people don't), don't add weed plants that have gone to seed or diseased plants, because you can transfer the problems to your garden. Don't add animal or human feces, which can spread disease.
Using Compost How do you know when the compost is ready? If you want to improve the soil's structure and ability to hold water and nutrients, let the organic matter break down until most of it is unrecognizable. Then use a spade or spading fork to turn a 2-3 inch layer of compost into the top 6-8 inches of soil in new beds for vegetables, flowers, and shrubs. For lawns spread a thin layer (up to an inch) on top of the grass in late fall or early spring. If you want bulky material to use as a mulch, interrupt the decay cycle earlier, while you can still identify some of the components. Because undecayed organic matter causes a growth spurt among the soil microorganisms, tying up some soil nutrients for awhile, it's best to put on partially aged compost after the fall harvest, so it can cook down more before spring. Apply a 1-3 inch layer on top of the soil around trees, shrubs, and perennial flowers.
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