Compost Fundamentals

Compost Needs

(Materials & methods to ensure quality compost)

particle size

Man using chipperShredding or grinding raw materials is beneficial, particularly when composting fibrous materials such as leaves, woody plants or corn stalks. Shredding exposes a greater surface area, which makes it more susceptible to bacterial invasion. Large pieces of wood or leaves packed together do not decompose quickly in a compost pile. Insufficient oxygen in the center of a wood chunk or a wad of leaves does not permit more rapid aerobic decomposition.

Shredding material makes it more uniform in size, aerates it, and makes it easier to handle and keep moist. Smaller particles enable the compost to heat more evenly, and to withstand excessive drying at the surface. The compost pile is then is insulated against heat loss, and also better resists moisture penetration from rain. Fly control is also better when material is pulverized or shredded. Uniform compost made from shredded material can be more easily applied to the land.

The best sized particles for composting are less than 2 inches in the largest dimension, but larger particles can be composted satisfactorily. The particle size of material being composted is determined by the finished product requirements and by economics. If the material is to be used on lawns or flower gardens, compost should be screened through a one-inch screen so it looks better and is easier to apply and work into the soil.

Sometimes it may not be worth added cost and labor to shred the material. Particles too large can be forked or screened out or broken up when necessary. Some people are not particular about uniformity of compost structure when preparing compost. For example, uniformity is not as important for agricultural fields as for the home gardener.

Initial shredding of all material is not absolutely necessary. Often, the best practice is to shred only large pieces of organic materials. Using some larger irregular pieces creates greater air spaces and hence more entrapped oxygen.

Large, tough feedstocks may require grinding to speed decompostition. Vegetative and herbaceous matter should not be ground up because it becomes soggy. The high moisture content of these materials makes them more difficult to manage in aerobic composting. The type of raw materials for composting determines when to shred.

Regrinding can be done either after the compost is mature, or near the end of the maturing process. Regrinding near the end of the period of active decomposition can serve as the last turning for aeration, and the pile can be left to stabilize.

Whether to grind or shred depends upon the nature of the raw material, the desired features of the final product--such as the appearance, size, and quality--and the economic requirements of the operation. Shredding and grinding the materials will shorten the decomposition time.

particle size effects on composting

carbon-nitrogen relationships

blending or proportioning

placement and structures

particle size




use of inocula

climatic conditions

Why Compost | Biology & Chemistry | Compost Needs
Composter's Needs | Benefits & Uses | Conclusion

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