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Making Compost


Compost is as good as gold to gardeners who know its value as a soil conditioner. It is decayed and partially decomposed organic matter and can be made from grass clippings, leaves, weeds and other organic waste products. It improves the soil in three main ways.

First, it encourages soil particles to clump together and provides better soil structure. This clumping increases drainage on poorly drained clay soil and allows oxygen to penetrate into the soil. Clumping also helps slow soil compaction.

Secondly, compost can improve sandy or gravelly soils. It acts like a sponge and increases the water holding capacity of the soil yet still allows for good drainage.

Finally, compost helps soil fertility. All compost no matter what vegetative material it's made from contains plants nutrients. Although the fertilizer value of compost is generally low, it does release nutrients as it decays, and, more importantly, holds nutrients in the soil until the plant roots can extract them. If it were not for decaying organic material in the soil, more nutrients would leach down past the plant roots were they are unusable by the plants.

Starting a compost pile is easy. In a small area you can build the pile in a simple chicken wire frame or more durable materials like plastic lumber or cement blocks. Most methods are based on layering organic materials in a pile and then turning the pile on a regular basis. Here's one way to build a compost pile. Use a well drained spot roughly 4 feet square. Place a layer of leaves or other plant material such as grass clippings and garden debris 10 to 12 inches deep, don't compact them too much. On top of the layer, spread about one half inch of garden soil. You can also use finished compost if you have some from a previous pile. Partially decomposed animal manure also makes a good addition. This thin layer inoculates the pile with the various microorganisms that do the actual decomposing.

If you are using mainly dried leaves or other dried material, sprinkle a handful or two of lawn or garden fertilizer on top of each layer. The fertilizer provides nitrogen which is necessary for the composting process. If 1/3 to 1/2 of your organic material is fresh and green, such as grass clippings or weeds, you needn't add the fertilizer as the green material will supply enough nitrogen.

Continue to build successive layers just like the first one until the pile is three to five feet tall. Water each layer as you complete it to keep the pile moist, don't over water though because excess water slows decomposition and can cause a pile to develop a bad smell. Your pile is moist enough if a handful of the pile feels like a damp sponge. Compost piles only smell when you build or manage them improperly. Also avoid making a compost pile mostly or entirely of grass clippings. Mix 50% or less grass clippings with dry materials such as leaves or wood chips, this will prevent the grass from developing a foul smell. If your compost pile does develop a bad smell, turn it. If the pile is too wet, add dry materials when turning the pile. This should eliminate the smell.

You can add vegetable and fruit scraps from the kitchen, but do not add meat scraps, cheese or table scraps to a compost pile. They will smell and attract dogs, flies and rodents.

Once the pile is built, all that's left to do is to turn your compost pile on a regular basis. Turn it about once a month from April through November. If you start a compost pile in the fall, and use the method discussed above, you should have a finished compost pile by the middle of next summer. You can speed up the process by turning the pile more frequently. The more work you put into the pile, the sooner you will have compost.

Missouri Botanical Garden, 2001-2011