- Compost is a dark, crumbly, earthy-smelling material produced by the natural decomposition of leaves, grass clippings, and many other organic materials.
- The composting process "happens" without human intervention because microbes and soil animals are on the job 24 hours a day, decomposing plant and animal remains.
- Composting allows you to expedite this natural process to produce a regular supply of compost (a.k.a. "black gold") for your landscape.
- Finished compost contains major and minor nutrients necessary for plant growth and also improves soil structure.
Why should I compost?
- It reduces the amount of material going to landfills. Municipal waste is composed of 13% yard wastes, 12% food waste, and 34% paper, most of which can be composted (U.S. EPA, Office of Solid Waste 2005).
- Compost is a valuable and free soil amendment that saves gardeners the money used to buy alternatives, such as peat moss, fertilizer, or vermiculite. It improves soil tilth (physical condition of the soil), aeration (reducing compaction, improving root growth and water penetration), water-holding capacity (important during droughts), and contains a wide range of plant nutrients. Most soils benefit from regular additions of compost.
- Compost suppresses some soil-borne diseases. Populations of some microbes in compost may out-compete pathogens for food and habitat while others attack or repel plant pathogens.
- It's good for the environment, fun, educational, and an activity the whole family can help with.
How is compost made?
- Bacteria, fungi, and other microbes are the key players in composting. These organisms "feed" on organic matter and use the carbon and nitrogen it contains to grow and reproduce.
- The heat generated by your compost pile is a result of microbial activity. Microbes are active in small numbers at temperatures just above freezing and are most numerous at 130º–140º F.
- They are assisted by many larger organisms like earthworms, slugs, snails, millipedes, sow bugs, ants, and various insect larvae that feed on plant and animal matter in the soil. These same organisms are responsible for the decay of both forest floor litter and the corn stubble in a farmer's field. Therefore, do not be alarmed if you find any in your compost pile. They are performing the initial breakdown of coarse materials - biting, chewing, decreasing the size of the materials, and thus increasing the surface area so that the microorganisms can do their work.
- Composting microbes use carbon for energy and nitrogen for growth (protein synthesis). When you mix various forms of organic material in your compost bin, it is important to achieve a proper balance of carbon to nitrogen (C:N ratio).
- The proportion can vary; the microbes will function well at C:N ratios from 25:1 to 40:1. A mixture of materials containing 30 parts of carbon to 1 part of nitrogen is considered ideal.
- Most organic materials do not fit the 30:1 ratio exactly, so different materials are mixed together. With the proper mix, microbes and other digesters will quickly start working to make compost for you. Finished compost has a C/N ratio of 20 - 25:1.
Carbon and nitrogen sources
|Carbon Sources (Browns)||Nitrogen Sources (Greens|
Cornstalks & corncobs
*Some organic materials are initially acidic
Materials that should not be composted
Wood ashes (large amounts
alters the pH)
Avoid adding lime to your compost pile/bin
as it can cause a chemical reaction that
releases nitrogen gas in the form of
ammonia, denying nitrogen to the
microorganisms that do the composting.
Types of composting
Before starting to compost, be aware of local ordinances! For example, in Baltimore County, you cannot compost food wastes above the ground (except in worm bins).
Cool or passive composting
- This method is not labor-intensive but requires patience.
- This process is carried out by a narrow range of microorganisms (mesophiles) that reproduce in the ambient (outdoor) temperature range, i.e., 40° F. to about 110° F.
- These microbes are thorough and produce excellent compost, but they need about a year to complete the process.
- If you constantly add fresh materials to your pile, the materials on top of the pile will be in the early stages of decomposition when the material at the bottom is ready to use.
- Remove the top of the pile and harvest the compost at the bottom annually, or start a new pile when the first pile is 3'x3'x3'.
- Don't build a pile over 5' high because the weight and volume will compact the organic wastes and limit air movement. This can cause smelly, anaerobic decomposition.
- Turn the pile once or twice a year, to hasten the process and create a more uniform product.
Hot or active composting
- This method produces a compost harvest in the shortest period of time but requires more careful attention and periodic labor.
- Hot composting usually involves a bin, or perhaps a pile, which is filled all at one time with the necessary ingredients without the addition of more raw materials later.
- The ideal bin size is a minimum of 3'x3'x3' or 27 cubic feet.
- A heap this size involves a broad range of microorganisms and generates significant heat.
- Once triggered into action and provided with the appropriate mixture of carbon (browns), nitrogen (greens), water, and air, the 'thermophiles' (heat-loving bacteria) will generate temperatures of 130-170° F., and will produce a compost harvest in six to eight weeks.
- The temperature will typically rise within 24 hours after the bin is filled. As the thermophiles consume nutrients and oxygen, they produce enough heat to evaporate some of the moisture.
- The temperature will decrease as they begin to die. This occurs when all of the easily digested sugars and starches are broken down and the tougher compounds like hemicellulose and cellulose remain.
- Before the temperature drops below 100° F., turn the materials so that fresh materials, air, and, if necessary, water are available at the core of the bin.
- In time, the volume of the original material will decrease. DO NOT add more raw materials unless the process is not working properly.
- Continue checking the temperature, turning, adding moisture, etc., until the volume of the material is about 50% of the original. The temperature will not rise again.
- The compost should be dark brown and should not resemble the original materials. Let the pile sit for two weeks, allowing the mesophiles to finish it off. This is known as curing and will help stabilize the nutrients.
Compost Temperature Control
- Temperature can be monitored in several ways. Compost thermometers are available for purchase.
- Or use your hand to monitor the temperature. If the pile feels cool when you thrust your hand into it, it probably needs to be turned. (The target temperature is 100º and body temperature is about 98.6°).
- If the pile/bin feels at least as hot as the hot water from your faucet, it is doing fine. If it feels really hot and has the aroma of ammonia, it may need a little more carbon, because excess nitrogen may cause anaerobic (no oxygen) decomposition that results in bad odor and more heat.
- This is an excellent method for creating a new bed in late summer for planting the following spring.
- Mow or weedeat the grass and weeds in the area as low as possible.,
- Place overlapping sections of newspaper or corrugated cardboard over the entire area.
- Spread a 2-4 inch layer of compost followed by a 4-8 inch layer of shredded leaves. You can also spread grass clippings (avoid weeds with seedheads and herbicide-treated turf).
- In spring, you'll be able to plant directly into the soil without the need for rototilling. Any leaves that have not broken down can be raked aside and used as mulch.
- This method uses up large amounts of locally-available organic material, requires some initial labor, does not require turning, and boosts the earthworm population.
- This method offers the small-plot vegetable gardener an opportunity to improve the soil on a continuous basis.
- Dig a trench or hole in a garden bed about eight to twelve inches deep.
- Bury your kitchen waste (fruit and vegetable peelings and cores, coffee grounds, etc.) covering the material as you go with soil or chopped leaves. Chopping the scraps with a shovel prior to covering will speed decomposition. The kitchen waste will feed soil animals and microorganisms increasing soil fertility.
- Rotate the location of the trenches and holes. It works best in fenced gardens that exclude raccoons, possums, and groundhogs.
- You can trench compost kitchen waste throughout the year although the process slows significantly from November through March.