Shredding of Refuse

Shredding or grinding the raw materials for composting can produce several beneficial results, particularly when using leaves, woody plants, corn stalks, and other bulky materials. Shredding or grinding organic materials makes it more susceptible to beneficial bacteria in the pile because a greater surface area is exposed and the natural defense resistance of vegetation against microbial invasion is disrupted. Moreover, a piece of wood, a pile of corn stalks, or leaves packed together take much longer to compost than do small particles of materials. Packed materials can also block sufficient oxygen from reaching the pile, slowing aerobic decomposition.

Shredding the material makes it more homogenous, produces better aeration and controls moisture. Shredded refuse heats more uniformly. It withstands excessive drying at the surface of the pile, is insulated against heat loss, and resists moisture penetration from rain better than does unshredded refuse. Fly control is also more easily accomplished when refuse is pulverized or shredded. Also, users of compost as mulch find that a shredded or ground material can be applied more readily and uniformly to the land.

The most desirable size of particles for composting is less than 2 inches, but larger particles can be composted satisfactorily. The particle size of the material being composted depends on the final use of the compost. 

However, on farms and large gardens, it is doubtful whether the advantages of shredding will be sufficient to justify the additional cost and labor. In ordinary composting any particles that are too large can be forked or screened out and broken up when necessary. If the material is to be used on lawns or flower gardens, it can be screened after composting
through a 1-inch or smaller screen to give it a better appearance and to make it easier to apply and work into the soil. The individual farmer or gardener may not be necessarily particular about the uniformity of the compost structure when preparing the compost. Nor is the uniformity as important for agriculture fields as for the hobby gardener.

Initial shredding of all the material is not necessary in the composting operation. It is often the best practice to limit the initial shredding to large pieces of organic materials. Some composters believe that permitting some larger irregular pieces to remain tends to create greater air spaces in the mass and entrap more oxygen. Undecomposed pieces can be screened out of the final compost and put back through the decomposing process.

Vegetative and herbaceous matter should not be ground because it becomes soggy. The high moisture content of these materials makes them useful in smallquantities throughout the composting process.