Compost Fundamentals

Compost Needs

(Materials & methods to ensure quality compost)

placement and structures

There are many ways, such as bins, barrels, pits and windrows to compost organic matter. Open piles, windrows, or bins are the most widely used methods for aerobic decomposition and maturing of organic refuse. Exact use and arrangement of these systems depends on local requirements of materials, labor, cost of systems, climatic conditions such as temperature, rainfall, and wind.

To aerobically maintain the composting process by frequent turning for aeration, windrows, piles and bins above the surface of the ground are more efficient than pits. On the other hand, if the decomposition is to be entirely anaerobic or aerobic only during a short initial period, pits 3 to 4 feet deep and varying in length and width in accordance with the daily quantity of raw material should be used.

Structures:
WINDROWS, PILES AND BINS

Material in aerobic composting piles should be loosely stacked to allow space for air in the interstices. Windrows or piles may be of any length, but the height of the pile is critical. If piled too high, material will be compressed by its own weight, thus reducing pore space, which results in increased turning labor (costs) or longer composting time as anaerobic conditions develop. In some instances, the maximum practical height may be governed by the equipment used for stacking the feedstocks, or by the tendency of the pile to become excessively hot. Large piles in warm weather may reach temperatures excessively high for bacterial life. Some have even caught fire.

Piles that are too low lose heat rapidly. They do not get hot enough for destruction of pathogenic organisms and decomposition by thermophiles
Also, if the piles are too small, loss of moisture may be excessive, especially near the edges, and decomposition slows.

Compost Pile

Five to six feet is about the maximum height for any pile, and 3 feet is the minimum for most shredded fresh organic matter. The height can be greater in cold weather than in warm weather.

Pile volume effects on compost graph

Thoroughly mixing compost materials in bins, windrows or piles provides quickest and most complete decomposition. The pile may normally be started directly on the ground. To ensure aeration to the bottom of the pile and improve drainage, dig a trench across the base of the area and cover with stiff wire mesh (hardware cloth) before adding material.

Home gardeners may not have enough materials daily for windrows. In this case circular or rectangular piles 4 – 6 feet in diameter and 3 to 5 feet high works, with a rounded top for shedding rainwater.

PITS

For shallow pits, either the walls and bottom of the pit are lined with brick or masonry or the natural earth is tamped and packed. The material is stacked to a height of 1 foot or more above the ground, making a total of 3 to 4 feet. The material can be turned in the pit as often as necessary to provide the high temperatures and aerobic conditions as required. When pits are used, a smaller stack surface is exposed to the air, and the walls and bottom of the pit provide some insulation against heat and moisture loss.

Any type of pit should be lined and is usually provided with a chimney and trenches, or a porous bottom, for aeration and drainage of liquid seepage from the pile. The same shape trenches without aeration and drainage channels and without masonry lining may be used. But unless pits are lined, the walls are apt to crumble and the shape of the pit becomes irregular. When hand labor is used, turning the material in a pit may be about the same as in a stack on the ground surface.

One effective method involves composting in pits approximately 3 feet deep by a system of providing aerobic conditions and high temperatures for the first few days and then anaerobic conditions for 4 to 6 months. Material is mixed in the pit. There is sufficient oxygen in the initial stack for a high temperature to be produced by aerobic organisms during the first few days. High temperatures are usually retained for two weeks or so, owing to the insulating properties of the stack, even though anaerobic conditions may exist after the first few days. Leave the material to compost in the pit with no turning for about three months.

SHEET or TRENCH COMPOST

To sheet compost, work a thin layer of material such as leaves into the garden in the fall. By spring, the material should be broken down. This would not be appropriate for materials such as wood chips that would take a longer time to decompose, and might tie up soil nitrogen in the spring, making it unavailable to other plants.

For trench compost, dig a trench 8 – 15 inches deep, bury the feedstocks, then cover back up with soil. It takes about a year to decompose.

 

carbon-nitrogen relationships

blending or proportioning

placement and structures

particle size

moisture

temperature

aeration

use of inocula

climatic conditions

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

Return to Whatcom County Composting

 
WSU Logo