Humus is the loose, crumbly material that results from the decay of organic matter -- leaves, grass clippings, garden waste, peat moss, or kitchen scraps. Because of its many desirable attributes, humus is extremely versatile and beneficial in the garden. Humus acts as the organic component of soil. Without it, soil is inactive and unable to produce plants, grass, or flowers.

To convert leaves, grass clippings and kitchen scraps into humus, you'll need to begin composting. As a soil amendment, compost improves soil structure and increases tilth, fertility, water holding capacity, aeration and drainage. To conserve moisture or develop a landscape requiring less water, it is essential to have soil with good water-retention. The real benefits of using compost are long-term and related to its contents of living organic matter. During the growing season in Colorado, a third or more of landfill waste is organic yard refuse. Home composting of yard and garden trimmings reduces the burdens on landfills and returns these organic materials to the soil. Following Mother Nature's example, Colorado gardeners can make compost easily.

How to make compost

Step 1 - Site location: Any pile of organic matter will eventually rot, but a well-chosen site can speed up the process. Try to locate the compost pile close to where it will be used, without offending neighbors.

Select a site that is convenient for adding materials and removing compost, yet one that does not detract from the landscape. Don't put it so far away you'll neglect the pile. The compost pile should be exposed to at least six hours of sunlight a day to trap solar heat. The pile will do best in the heat of partial sunlight, but away from drying winds. Water should be readily available. Good drainage is also important, since standing water can slow the decomposition process. Build the pile over soil or lawn rather than concrete or asphalt, to take advantage of the earthworms, beneficial microbes, and other decomposers which will migrate up in the pile and back down as the seasons change.

Step 2 - Compost container selection: Structures aren't necessary for composting but do prevent wind and animals from carrying away plant wastes. Many containers are suitable, provided that they resist decay, allow airflow and are accessible. Most compost methods fall into one of these categories: heaps (simple stacked piles), hoops (caged enclosures), bins (boxed enclosures), and barrels (drum enclosures). To decide which container will work best for you request Fact sheet 7.212 - "Composting yard waste" or visit the web sites listed below.

Step 3 - Raw materials selection: Yard and garden debris, kitchen wastes such as vegetable scraps, coffee grounds, eggshells and other organic materials are suitable for composting. If it can rot, it will compost. Green material, like leaves, grass clippings and soft young weeds rot quickly. They work as 'activators', getting the composting started. Older and tougher plant material decomposes more slowly. Woody items decay very slowly; they are best omitted or finely chopped or shredded first. For best results, use a mixture of ingredients.

Traditional composting includes soil as an ingredient. Large amounts of soil add unnecessary weight. While soil can serve as a source of microbes to "inoculate" plant wastes, research has found that microorganisms that break down plants also are present on the surface of leaves and stems. It is natural for some soil to cling to uprooted plants. There is no advantage in adding commercial compost starters or inoculums to compost piles. To make compost without soil, alternate green and brown types of shredded plant materials in six- to eight-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. Layering is traditional, but mixing the materials works as well.

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 without weed killers. If materials accumulate over time, add new materials to the center of the pile. This practice will help aerate the center of the pile, where anaerobic conditions are likely to occur.

Avoid meat scraps, bones, grease, whole eggs, or dairy products in the compost pile because they are slow to decompose, will cause odors, and can attract rodents. Due to the possibility of disease transmission, human, dog, and cat feces should not be placed in compost piles. Diseased plant material or weeds that have gone to seed also are undesirable. Black and white newsprint is best recycled through recycling collection operations rather than being converted to compost.

Step 4 - Aeration: Composting consumes large amounts of oxygen, particularly during the initial stages. Most of the organisms that decompose organic matter are aerobic - they need air to survive. If the supply of oxygen is limited, the composting process may turn anaerobic, which is a much slower and more odorous process. Lifting and turning the materials with a pitchfork or a mechanical aerator tool will replenish oxygen levels. Try to move drier materials from the outside of the pile into the center. Weekly turning can produce compost in a shorter time period. With the right moisture level and combination of materials, regular turning will produce compost in about four to six months. Without turning and aerating, composting may take six months to two years.

Step 5 - Keeping it moist: Moisture is necessary to support the metabolic processes of microorganisms. Composting materials should be kept moist. As a rule of thumb, materials are too wet if water can be squeezed out of a handful of compost and too dry if the handful does not feel moist to the touch. If the compost pile is too dry, the process slows down. Too much water is just as detrimental as the lack of water. In an overly wet pile, water replaces the air, creating an anaerobic environment, slowing decomposition. Moisture content generally decreases as composting proceeds, so you may need to periodically add water to the compost. Some people cover their compost with plastic to prevent the outer layers from drying too much. Remove covers periodically to add more water and plant material and to aerate.

Step 6 - Temperature: The temperature of the tended pile is important; it indicates the activity of the decomposition process. The easiest way to track the temperature inside the pile is by feeling it. If it is warm or hot, everything is fine. If it is the same temperature as the outside air, the microbial activity has slowed down and you need to add more nitrogen (green) materials such as grass clippings, kitchen waste, or manure. Composting will essentially take place within two temperature ranges, known as mesophilic (50-105°F) and thermophilic (over 105°F). Keeping temperatures between 110 and 150°F destroys more pathogens and weed seeds in the compost. Compost thermometers are available at specialty garden shops and nurseries.

Step 7 - Curing: Finished compost is dark, crumbly, and has a rich, earthy, inoffensive odor. Curing refers to finished compost left in a pile undisturbed for up to one month, allowing any final chemical and decomposition reactions to occur. Curing ensures that the composting process is indeed complete and that potential problems are minimized. To bolster poor soil with little organic matter, spread 2 to 3 inches of compost over a newly dug surface. Then work the compost into the top 6 inches of earth. Garden soil that has been well mulched and amended periodically requires only about one-half inch layer of compost yearly to maintain its quality. You'll be amazed at how much better your plants will grow. Remember that compost is a soil amendment, not a fertilizer. It contains limited plant nutrients.

Summary

Compost is an excellent, inexpensive way to increase the productivity and workability of soil. It reduces and recycles yard waste and produces a valuable soil amendment. The real benefits of using compost are long-term and related to its content of living organic matter. Help the garden, the environment, and save dollars by composting lawn and garden waste.

Fact sheets that relate to this column are: 7.212 - "Composting Yard Waste" and 7.007, "Eliminate Grass Clipping Collection."

You may also call Planttalk Colorado at 1-888-666-3063 and request topics number on composting. Planttalk Colorado is a 24-hour toll-free automated phone service that provides you with reliable, timely information on a variety of horticultural topics. Or if you would like the printed version, click on the links below:

1612: Composting: fall leaves
1613: Composting: making
1614: Composting: using
1615: Composting: what can be composted
1622: Composting: worm composting
1623: Composting: structures

Other gardening topics may be found at:
Planttalk Colorado

Additional composting information can be found at:
City of Fort Collins: Composting Yard Waste

Q: Is it really necessary to clean up leaves in my yard? Why not just leave them on the lawn to disintegrate into organic matter?

A: Leaves and other debris left on your lawn can block vital sunlight needed by your turf grass. Fallen debris from your trees may also harbor fungus that will produce spores in the spring. Raking and destroying infected leaves can reduce Marssonina leaf spot, ink spot and leaf rust, which are common among our poplar species. If fungus is not a concern, a mulching mower is a good way to return the leaves to the soil.

Q: Is it safe to divide and transplant my peonies now or should I wait until spring?

A: Mid-September through mid-October is a good time to separate and transplant spring and early-summer blooming perennials, such as peonies. If dividing the plant, make sure each piece of the tuberous rootstock has 3 to 5 eyes or buds. Plant them no more than 1 to 2 inches deep, otherwise they will not bloom.

Q: What is the difference between core aeration and power-raking, and when should it be done?

A: Both are techniques for managing thatch buildup in your lawn and, when used properly, can help improve the growing conditions for turf grasses. Thatch can become a problem on Kentucky bluegrass, bentgrass and fine fescue lawns if it becomes thicker than one-half inch. However, clippings do not contribute to thatch buildup and should be recycled in your lawn to benefit from the nutrients they contain.

Light power raking may be beneficial if done often. Deep power raking can be damaging as it may remove living turf along with the layer of thatch. Core aeration is more beneficial than power raking because it not only helps improve the root zone by relieving soil compaction but also helps control thatch accumulation. Fall is an excellent time for aeration and is a good first step in overseeding an existing turf area.

If you've noticed large numbers of millipedes "migrating" into your home in recent weeks, don't be alarmed. Other than being a minor annoyance, they are not harmful to humans. Millipedes often move into homes following wet, cool spells in fall and spring. With the low humidity found in most Colorado homes, the millipedes will dry out in 1-2 days and can easily be swept or vacuumed up. The millipede "migration" usually only lasts for a short period of time and ends almost as suddenly as it begins. To reduce future migrations of millipedes into your home, remove any suitable habitat (logs, rocks, mulch) from around the foundation and seal or caulk any openings around the foundation.

Most urban dwellers have a love / hate relationship with squirrels. While squirrels can be quite entertaining to watch, as they frolic about in the yard, they may occasionally cause damage to urban landscapes. During the spring, when trees are in bud, squirrels prefer the succulent, swelling buds to most other food choices. During the summer, squirrels typically eat fruits, vegetables, small insects, and succulent herbaceous plant material. In the fall and winter months, if their stored food supply is inadequate to carry them through until spring, squirrels often resort to eating bark, sometimes girdling whole branches which will subsequently die. Lawns also may be damaged from squirrels storing and digging for food. Squirrels are protected by law and may only be live-trapped and relocated. Repellents may offer some short-term reprieve from squirrel damage, but most are only marginally effective and must be reapplied often. The best option may be for urban dwellers to learn to share their garden spaces with squirrels.

If you have seeds leftover from this season's garden, most can be saved and planted next season without appreciable loss of germination or quality. If you want to save seeds for several years, you will need to dry the seeds and store them in moisture-proof containers in the refrigerator or freezer. To dry the seeds for storage, place them in a single-layer on a cookie sheet and place them in a conventional oven warmed to 100°F for six hours. It is best to keep the oven door open while drying the seeds to prevent possible overheating. Do not attempt to dry seeds in a microwave oven.

The authors have received training through Colorado State University Cooperative Extension's Master Gardener program and is a Master Gardener volunteer for Larimer County.

Gardening and Insect Fact Sheets are available on-line by clicking HERE.

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This page updated:  October 11, 2004