compost demo
Updated: July 12, 2024

About making compost

  • 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?

composting infographic
  • 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, nitrogen sources, and items not to compost

Carbon Sources (Browns)

Cornstalks & corncobs
Dry leaves*
Newsprint

Pine needles
Straw & hay 
Sawdust 
Wood chips 
Shrub trimmings 
Shredded copier paper (Uncoated)

*Some organic materials are initially acidic
(low pH) like oak leaves. However, the composting
process results in a finished product with a pH of
around 7.0, or neutral pH.
Nitrogen Sources (Greens)

Coffee grounds and tea leaves*

Crab/fish waste - Trench method only
Fruit & vegetable scraps
Grass clippings (untreated)
Fresh hay
Manure: cow, horse, poultry, sheep, rabbit 
Seaweed

*Check labels; many tea bags contain plastics

and should not be composted.
Items not to compost Bones                                    
Cheese
Cooking oil
Dairy products
Lard
Mayonnaise
Meat products
Milk
Peanut butter
Salad dressing
Cleaning solvents
Pet feces
Petroleum products
Plastic
Soil
Synthetic fabrics
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

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.

Sheet composting

  • This is an excellent method for creating a new bed in late summer for planting the following spring.
  • Mow or weed-eat the grass and weeds in the area as low as possible.,
  • Place overlapping sections of newspaper or unwaxed corrugated cardboard over the entire area.
  • Cover with 8 inches of one or more of the following: compost, aged manure, shredded leaves, or 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. 
  • This method uses up large amounts of locally-available organic material, requires some initial labor, does not require turning, and boosts the earthworm population.

Trench composting

  • 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. Note: many tea bags contain plastics. Only plastic-free tea bags should be composted. Otherwise, open the tea bags, empty the contents into your food scraps bucket, and dispose of the bags as trash.
  • 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.

Instructions for a wire compost bin

wire bin composter illustration

Composting tips

  • Locate compost bins and piles away from trees to reduce the likelihood of roots growing into the compost.
  • Mix materials thoroughly; it's usually not helpful to layer materials.
  • To speed up the process you can add an extra nitrogen (e.g., cottonseed meal, blood meal) source at each turning.
  • Keep your compost pile moist (like a wrung-out sponge) but not soggy for efficient decomposition. Excess moisture causes anaerobic decomposition and offensive odors. During dry weather, it may be necessary to add water at weekly intervals.
  • Do not add branches and other woody materials unless they are chipped into small pieces.
  • In dry weather, cover the pile to prevent excess moisture loss and to aid decomposition. A tarp or other cover also protects the pile from becoming too wet during periods of heavy rainfall and helps prevent nutrient leaching.
  • Turn or mix the pile regularly. If fall-gathered leaves make up the bulk of the pile, turn the pile in mid-November before freezing occurs. Do not turn the pile in winter because this allows too much heat to escape and slows decomposition.
  • When kitchen scraps are collected or composted it can be helpful to mix in a dry, high-carbon material, such as leaves, sawdust, or shredded paper, to reduce odors and facilitate decomposition.
  • Enclosed compost tumblers can quickly become soppy wet and anaerobic if you add too many kitchen scraps and rotted fruits and vegetables, and not enough brown materials.

Comparison of composting methods

Type Advantages Disadvantages
Hot Quicker harvest. Kills many weed seeds and diseases. Less likely to attract unwanted animals. Requires careful attention and frequent labor. Requires storage of some materials prior to use.
(Most carbon sources can easily be stored for
many months.)
Cool Materials added as generated. Less labor. Compost rich in beneficial organisms. Takes a year or more. Some nutrients lost to leaching. Can attract animals and flies.
Bin Neat and tidy appearance. Can be used for either hot or cool methods. Must purchase or fabricate. May be difficult to turn in materials. Generally requires more labor than other methods.
Tumbler Neat and tidy. Good for maintaining aeration. Works well for cool composting. Good for small spaces. Costly. Volume is usually inadequate for hot composting. Filling and/or harvesting may be awkward. Requires close attention.
Worm Composting
(Vermicomposting) 		 Easy. Little or no odor. Can be done indoors or outdoors. Rich product. Excellent way to compost food waste. Requires careful attention to food materials added. Must provide suitable location and temperature for worms; may attract fruit flies.
Sheet Composting No turning required. Boosts earthworm population. Requires timing and patience. Requires some initial labor. May not be ready for planting when anticipated.
Trench Composting Easy. Boosts number of earthworms. Doesn’t attract flies. Requires planning, persistence, and regular trips to the garden.

When is compost ready to use and how can I use it in my yard?

  • When the material is even in color and texture and has an earthy smell with no "off" odors.
  • When the temperature of the pile is at the outdoor temperature.
  • When a small amount placed in a plastic bag and sealed causes no condensation of moisture inside the bag.
  • Incorporate it into the soil as a soil amendment. Add to established beds or when creating beds.
  • Use two inches of compost as mulch around landscape plants to keep the soil cooler, retain moisture, and add nutrients to the plants over the course of the growing season.
  • Grow vegetable and flower transplants and container plants in screened compost. Try a mixture of 50% compost and 50% commercial soilless growing media.
  • Use it to make compost tea, which has multiple benefits to plants and soil. Applying it to the soil around plants or spraying it on foliage applies beneficial microbes that could suppress the colonization of disease-causing fungi. Compost tea also contains small amounts of organic nutrients necessary to the health of plants. It encourages earthworm activity and will enhance the population of soil microbes.

How to make compost tea

Compost tea is made by "steeping" compost in a bucket of water (5 parts water to 1 part compost by volume) for 1-3 days, then straining and applying the liquid to plants. Make compost tea using composted yard waste (leaves, grass clippings, etc.) or vermicompost (worm compost). Do not use farm animal manure compost. It is low in a wide range of nutrients and good for fertilizing seedlings and transplants.

Based on HG 35 Backyard Composting, author former HGIC Consultant Lew Shell. Reviewed by Jon Traunfeld, Director HGIC, Extension Specialist, Fruits and Vegetables.
Rev. 9/2020

Related information

Organic Matter and Soil Amendments

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