Courtesy of Colorado State University Extension

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November 20, 2013
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CSU Extension Tips: Composting fall leaves, other yard waste

Fall leaves are a valuable resource because they keep garden soil productive.

By following a few tried and true composting techniques, you can optimize fall-leaf composting.

The minimum size for compost bins is 3 feet by 3 feet by 3 feet. Bins larger than 6 feet across may restrict oxygen infiltration and slow decomposition.

It’s best to mix some nitrogen into the leaves as you add them to the compost. Leaves are high in carbon, which makes great compost, but they’re comparatively low in nitrogen, and that’s what decomposing bacteria feed on.

You can add nitrogen in the form of fertilizer or fresh green organic matter. Just add one-quarter to one-half cup of standard lawn fertilizer per bushel, or add one part dry leaves with two parts fresh grass clippings or similar green garden debris.

If you use a fertilizer, be sure to select one that doesn’t contain any weed killers.

As you add leaves to the compost, moisten them until they’re the consistency of a wet sponge. Check the compost regularly and water to maintain adequate moisture content. Moisture is slow to soak through a leaf pile and is essential for decomposition.

Be careful not to over-water, because you don’t want the leaves to be soggy.

Whole leaves are better for compost than leaves that are shredded or mulched with a lawn mower. Finely chopped leaves may pack down excessively in the compost bin, restricting oxygen infiltration necessary for decomposition.

By following these simple guidelines, you can produce fall-leaf compost by late spring. An unattended a pile of leaves may take two to three years to decompose.

Composting All Yard Waste

All yards produce waste from pruning, lawn mowing and other routine plant care activities. Composting is a way to reduce the volume of organic wastes and return them to the soil to benefit growing plants.

Organic matter improves the drainage and aeration of clay soil. Compost can be thought of as a separator that “shoulders apart” tightly packed clay particles to allow water and air to enter.

Composting helps sandy soil hold water and nutrients.

Compost holds moisture “like a sponge” and releases fertilizer nutrients slowly. It also increases the activity of earthworms and other natural soil organisms that are beneficial to plant growth.

Note: Compost is a soil amendment, not a fertilizer. It contains limited plant nutrients.

Making Compost

To make traditional compost, alternate different types of shredded plant materials in 6- to 8-inch layers. Layering helps compost reach the correct nitrogen balance. Use equal parts by volume of dry and green plant materials in the overall mix.

Use caution when you add layers of fine green plant wastes such as grass clippings. Grass mats easily and prevents water from moving through the mass.

Use 2-inch layers of fine materials or process them through a machine shredder. Alternate fine materials with woody plant prunings to prevent clogging the machine and to create an equal balance of dry and green materials.

Traditional composting includes soil as one of the layers. While soil can serve as a source of microbes to “inoculate” plant wastes, research has found that the microorganisms that break down plants also are present on the surface of the leaves and stems.

It’s natural for some soil to cling to pulled weeds and uprooted vegetable and flower plants. When you add large amounts of soil, you increase the weight, which makes composting difficult and less efficient.

Large amounts of soil also can suffocate microorganisms. Soilless composting is often practiced.

Add water to the compost after every few layers of material.

If the plant materials are dry and no green material is available, add a small quantity of blood meal or a commercial nitrogen fertilizer free of weed killers. One-half cup of ammonium sulfate per bushel of material is sufficient. Livestock manure also can be added and supplies some nitrogen.

Like soil, manure adds weight and bulk. The space devoted to manure could be used to compost yard wastes.

There is no advantage in adding compost starters or inoculum to the compost. The microbes that cause decomposition multiply just as rapidly from those that are naturally found on the plant waste.

Materials to Use and Avoid

A variety of materials can be composted, but most gardeners want to recycle collected yard waste. Plants lose between 50 and 75 percent of their volume in composting, so a lot of plant material can be processed effectively.

Composting can be effective on most yard wastes such as leaves, vegetable and flower plant parts, straw, and a limited amount of woody prunings, grass clippings and weeds. Woody twigs and branches that are greater than 1/4 inch in diameter should first be put through a shredder-chipper.

Avoid highly resinous wood and leaf prunings from plants such as junipers, pine, spruce and arborvitae. The resins protect these materials from decomposition and extend the time needed for composting in comparison with other plant materials.

High tannin-containing leaves (oak and cottonwood) have similar problems but can be used in small quantities if chopped well and mixed with other materials. The easiest way to handle grass clippings is to leave them on the lawn.

Research shows that they return valuable nutrients back to the soil. Some grass clippings can be used for compost if other green plant material isn’t available.

Many, but not all, plant disease organisms are killed if the compost reaches 122 degrees. Temperatures will vary throughout the compost.

Outer layers stay cooler than the center and cause uneven kill of disease organisms. If a plant is severely diseased, it is better to dispose of it in the trash.

In general, avoid plants treated with weed killers.

Small amounts of herbicide-treated plants may be mixed in the pile as long as you allow for thorough decomposition. Weed killers and other pesticides break down at various rates.

If you use treated grass clippings, the breakdown of these chemicals should be at least as fast as breakdown in the soil. Plants killed with weed killers that are soil inactive (glyphosate products such as Roundup or Kleenup) should present no problem when composted in small quantities.

In addition to yard wastes, many people compost kitchen wastes, such as vegetable scraps, coffee grounds and eggshells. These materials compost well and usually are not produced in large enough quantities to displace yard wastes.

Animal wastes (meat, bones, grease, whole eggs and dairy products) may cause odors and attract rodents; they are not recommended.

Human, cat or dog feces may transmit diseases and should not be used. Some animal products that can be used as organic sources of nitrogen include blood and steamed bone meal and livestock manures from plant-eating animals (cows, sheep, rabbits and chickens).

Manures may contain new strains of E. coli and other bacteria that cause human illness. The use of manures added directly to the food garden is questionable, although use on ornamental plantings is still recommended.

Research shows that 2 to 10 percent of bacterial pathogens survive the composting process.

If manure is composted for food gardens, a two- to four-month curing process following composting is necessary to reduce pathogens. Favorable moisture and temperature conditions during curing allow microorganisms to develop and out compete the pathogens. Thoroughly wash all fruits and vegetables and peel according to safe food handling practices to minimize the possibility of bacteria-contaminated soil being carried into food prepared for human consumption.

Black and white newsprint is best recycled through recycling collection operations rather than converted to compost.

If paper is composted due to a shortage of dry materials, add no more than 10 percent of the total weight of the material being composted. Do not use wood ashes or lime for composting in Colorado. Both increase salt and alkalinity, which leads to a loss of nitrogen in the form of ammonia gas.

Catching and bagging grass clippings is not worth the effort when they are easily recycled right on the lawn. If clippings are too long to leave on a lawn, composting is a better alternative than disposal in the trash.

Some weeds can be composted, particularly if they are pulled before they produce seed. Compost mainly serves to reduce the volume of yard wastes and convert plant materials into a usable soil amendment.

Adding excessive amounts of other materials, such as animal manures, defeats the purpose. ❖

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The Fence Post Updated Nov 15, 2013 10:48AM Published Dec 5, 2013 05:00PM Copyright 2013 The Fence Post. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.