Horticulture Principles and Practices

662 Chapter 22 Organic Farming
metabolic activities cause the temperature to increase. A temperature range of between
21.1 and 32.2°C (70 and 90°F) ushers in another group of microbes called mesophiles.
Mesophiles are the workhorses of composting. However, at 37.8°C (100°F), they are
replaced by thermophiles, heat-loving bacteria that work to raise the temperature of the
compost heap to a much higher level, reaching a peak of about 71.1°C (160°F).
After bacteria have operated on the organic matter, cellulose, lignin, and other hardto-metabolize
substances are left behind in the pile. Fungi and actinomycetes are able to
decompose these substances. Their presence in the heap is indicated by the occurrence
of whitish strands or cobweblike structures.
Larger microorganisms such as earthworms are important in the compost heap.
They feed on organic matter and excrete materials rich in nutrients for plant growth.
Earthworms abound in soils that have high microbial activity.
22.14.3 COMPOSTABLE MATERIAL
The quality of compost depends in part on the materials included in the compost heap.
The secret to quality is variety. Avoid including too much of one type of material. Good
compostable materials include the following:
1. Grass clippings from mowing a lawn. A mulching mower may be used to spread
fine clippings on the soil. When clippings are bagged, they may be used as a
good source of plant material for composting, provided a few cautions are
observed. Do not use clippings from a lawn that has been recently sprayed with
pesticides. A fresh pile of grass clippings has a tendency to form a slimy and
soggy product with a foul odor. It is best to spread grass clippings in thin layers
or to mix them in with dry leaves.
2. Household garbage that is void of fats and oil. Greasy materials are hard for
microbes to metabolize.
3. Leaves. During the fall season, leaves drop from trees. Dry leaves may be
gathered for use in composting. Leaves decompose slowly and need some help
to accelerate their breakdown. Instead of using full-size leaves, they should be
chopped before adding them to the compost pile. Leaves should be added in thin
layers.
4. Sawdust. Sawdust from softwoods, pine, and cedar decompose more quickly
than those from hardwood (e.g., birch and oak). When including sawdust,
it should be sprinkled lightly and in layers like the other materials.
5. Straw or hay. Old (highly weathered), not fresh, hay makes a good compost
material. Straw or hay should be chopped before adding it to the pile.
6. Ash. Wood ash from the fireplace contains potash and is a good material to
include in a compost heap.
22.14.4 MATERIALS TO AVOID
Some materials are undesirable in a compost heap because they either are not
biodegradable or produce toxic factors that are harmful to microbes. These materials
include:
1. Diseased plants. All pathogens may not be killed by the heat generated, even at
the peak temperature of about 71.1°C (160°F).
2. All nonbiodegradable material (e.g., plastics, synthetic cloths, and styrofoam).
3. Pesticides. Pesticides should not be used under any circumstance because they
destroy the organisms that are the agents of decomposition.
4. Pet litter.
Other materials should be used with caution. For example, the plant remains from
corn harvest, including cobs and husks, are hard to decompose. If they must be added,
they should first be chopped into small pieces.