How Much Does Composting Produce?

Composting Process

• Compost occurs from a natural process during which microorganisms break down dead organic materials, releasing nutrients as they do so. Without this process, twigs, branches, fallen leaves and other dead plant and animal matter would linger perpetually, cluttering the fields and forests. However, because composting is a breakdown process, you can't expect that the amount of raw materials you put into your compost pile will result in an equal amount of compost. You should take changes in pile size into account when planning to meet your compost needs.

Pile Shrinkage

• As soil microbes and larger soil critters like earthworms gobble up organic raw materials and turn them into compost, far less remains than you started with. This causes a compost pile to appear to shrink as the compost ages. By the time you achieve finished compost, your compost pile will appear about half the size as it did when you began. However, the pile loses far more in volume than it does dimensions. According to the University of Missouri Extension, finished compost shrinks 70 to 80 percent in volume as it ages. If you know you need a specific volume of compost, therefore, you should plan to compost five times the volume of raw ingredients.

Nutritional Value

• Gardeners also need to know how much their compost contributes to the nutritional health of the garden soil. Finished compost contains between 0.5 and 4 percent each of the three macronutrients plants require: nitrogen, phosphorus and potassium. These levels are inadequate for many ornamental and vegetable plants, so you'll need to add fertilizer in addition to compost in most cases.

Improving Nutrient Levels

• You can produce compost with higher nutrient levels, however, by adding materials like livestock manures that contain high nutrient content. Many factors determine the amount of nutrients in your compost if you include manure. The type of livestock determines the nutrient levels, particularly nitrogen. Chicken manure, for example, contains higher levels of nitrogen than horse and cow manure. The amount of carbon-rich materials -- ingredients such as sawdust or dried leaves -- also influences the availability of nutrients, with high levels of carbon-rich materials diluting the nutrients found in the manure.