How to compost biodegradable waste?

Tuula Virman-Ojanen, Helsinki, Finland
Published on 2008.07.21


The purpose of this article is to provide a concise guide to making your own compost. There are excellent guides on composting available and here we attempt to translate the compost guide published in Finnish by YTV and put together some material from Compostguide.

1. Why make compost?

Compost is one of nature's best mulches and soil amendments, and you can use it instead of commercial fertilizers. Best of all, compost is cheap. You can make it without spending a cent. Using compost improves soil structure, texture, and aeration and increases the soil's water-holding capacity. Compost loosens clay soils and helps sandy soils retain water. Adding compost improves soil fertility and stimulates healthy root development in plants. The organic matter provided in compost provides food for microorganisms, which keeps the soil in a healthy, balanced condition. Nitrogen, potassium, and phosphorus will be produced naturally by the feeding of microorganisms, so few if any soil amendments will need to be added.

Most gardeners have long understood the value of this rich, dark, earthy material in improving the soil and creating a healthful environment for plants. Understanding how to make and use compost is in the public interest, as the problem of waste disposal climbs toward a crisis level. Landfills are brimming, and new sites are not likely to be easily found. For this reason there is an interest in conserving existing landfill space and in developing alternative methods of dealing with waste. Don't throw away materials when you can use them to improve your lawn and garden! Start composting instead.

2. How to build compost bin?

You may build your own composting bin for garden & household biowaste. The simplest compost bin is a wooden box covered by a plastic cover with holes and a compost bin which can be used in rotation is a box with several compartments. Fill one of the compartments with new waste, while previous year's waste is mouldering in another compartment. Both these types of bins are shown below.

Wooden box Box with compartments
A wooden box covered by a plastic (picture: YTV/Anssi Keränen) A box with several compartments (picture: YTV/Anssi Keränen)

Drying material, same amount as waste,  is needed to absorb humidity and smell and to create carbon for the compost. For example chopped straw or branches and bark of trees can be used for this purpose.

Compost is the end product of a complex feeding pattern involving hundreds of different organisms, including bacteria, fungi, worms, and insects. What remains after these organisms break down organic materials is the rich, earthy substance your garden will love. Composting replicates nature's natural system of breaking down materials on the forest floor. In every forest, grassland, jungle, and garden, plants die, fall to the ground, and decay. They are slowly dismantled by the small organisms living in the soil. Eventually these plant parts disappear into the brown crumbly forest floor. This humus keeps the soil light and fluffy.

Humus is our goal when we start composting. By providing the right environment for the organisms in the compost pile, it is possible to produce excellent compost. We usually want to organize and hasten Mother Nature's process. By knowing the optimum conditions of heat, moisture, air, and materials, we can speed up the composting process. Besides producing more good soil faster, making the compost faster creates heat which will destroy plant diseases and weed seeds in the pile.

3. Making Compost

Compost can range from passive - allowing the materials to sit and rot on their own - to highly managed. Whenever you intervene in the process, you're managing the compost. How you compost is determined by your goal. If you're eager to produce as much compost as possible to use regularly in your garden, you may opt for a more hands-on method of composting. If your goal is to dispose of yard waste, a passive method is your answer.

Passive composting involves the least amount of time and energy on your part. This is done by collecting organic materials in a freestanding pile. It might take a long time (a year or two), but eventually organic materials in any type of a pile will break down into finished compost. More attractive than a big pile of materials sitting in your yard is a 3-sided enclosure made of fencing, wire, or concrete blocks, which keeps the pile neater and less unsightly. Add grass clippings, leaves, and kitchen scraps (always cover these with 8" of other material). The pile will shrink quickly as the materials compress and decompose. Wait a year or two before checking the bottom of the bin for finished compost. When it's ready, shovel the bottom section into a wheelbarrow and add it to your garden beds. Continue to add greens and browns to have a good supply of finished compost at the ready. After the first few years, most simple piles produce a few cubic feet of finished compost yearly.

Managed composting involves active participation, ranging from turning the pile occasionally to a major commitment of time and energy. If you use all the techniques of managing the pile, you can get finished compost in 3-4 weeks. Choose the techniques that reflect how much you want to intervene in the decomposition process and that will be a function of how fast you want to produce compost.

The speed with which you produce finished compost will be determined by how you collect materials, whether you chop them up, how you mix them together, and so on. Achieving a good balance of carbon and nitrogen is easier if you build the pile all at once. Layering is traditional, but mixing the materials works as well.

Shredded organic materials heat up rapidly, decompose quickly, and produce a uniform compost. The decomposition rate increases with the size of the composting materials. If you want the pile to decay faster, chop up large fibrous materials.

You can add new materials on an ongoing basis to an already established pile. Most single-bin gardeners build an initial pile and add more ingredients on top as they become available.

The temperature of the managed 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.

If the pile becomes too dry, the decay process will slow down. Organic waste needs water to decompose. The rule of thumb is to keep the pile as moist as a wrung-out sponge. If you're building your pile with very wet materials, mix them with dry materials as you build. If all the material is very dry, soak it with a hose as you build. Whenever you turn the pile, check it for moisture and add water as necessary. 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.

Air circulation is an important element in a compost pile. Most of the organisms that decompose organic matter are aerobic - they need air to survive. There are several ways to keep your pile breathing. Try not to use materials that are easily compacted such as ashes or sawdust, without mixing them with a coarser material first. People who build large piles often add tree branches or even ventilation tubes vertically into different parts of the pile, to be shaken occasionally, to maximize air circulation.

4. Compost site selection

Any pile of organic matter will eventually rot, but a well-chosen site can speed up the process. Look for a level, well-drained area. If you plan to add kitchen scraps, keep it accessible to the back door. Don't put it so far away you'll neglect the pile. In cooler latitudes, keep the pile in a sunny spot to trap solar heat. Look for some shelter to protect the pile from freezing cold winds which could slow down the decaying process. In warm, dry latitudes, shelter the pile in a shadier spot so it doesn't dry out too quickly.

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 and down as the seasons change. Uncovered soil also allows for drainage. If tree roots are extending their roots into the pile, turn it frequently so they can't make headway.

Look for a spot that allows you to compost discretely, especially if you have neighboring yards in close proximity. Aim for distance and visual barriers between the pile and the neighbors.

5. Compost Materials

Almost any organic material is suitable for a compost pile. The pile needs a proper ratio of carbon-rich materials, or "browns," and nitrogen-rich materials, or "greens." Among the brown materials are dried leaves, straw, and wood chips. Nitrogen materials are fresh or green, such as grass clippings and kitchen scraps.

Mixing certain types of materials or changing the proportions can make a difference in the rate of decomposition. Achieving the best mix is more an art gained through experience than an exact science. The ideal ratio approaches 25 parts browns to 1 part greens. Judge the amounts roughly equal by weight. Too much carbon will cause the pile to break down too slowly, while too much nitrogen can cause odor. The carbon provides energy for the microbes, and the nitrogen provides protein.

Leaves represent a large percentage of total yard waste. They are loaded with minerals brought up from the tree roots and are a natural source of carbon. A few leaf species such as live oak, southern magnolia, and holly trees are too tough and leathery for easy composting. Avoid all parts of the black walnut tree as they contain a plant poison that survives composting. Eucalyptus leaves can be toxic to other plants. And avoid using poison oak, poison ivy, and sumac.

Pine Needles need to be chopped or shredded, as they decompose slowly. They are covered with a thick, waxy coating. In very large quantities, they can acidify your compost, which would be a good thing if you have alkaline soils.

Grass Clippings break down quickly and contain as much nitrogen as manure. Since fresh grass clippings will clump together, become anerobic, and start to smell, mix them with plenty of brown material. If you have a lot of grass clippings to compost, spread them on the driveway or other surface to bake in the sun for at least a day. Once it begins to turn pale or straw-like, it can be used without danger of souring. Avoid grass clippings that contain pesticide or herbicide residue, unless a steady rain has washed the residue from the grass blades.

Kitchen Refuse includes melon rinds, carrot peelings, tea bags, apple cores, banana peels - almost everything that cycles through your kitchen. The average household produces more than 200 pounds of kitchen waste every year. You can successfully compost all forms of kitchen waste. However, meat, meat products, dairy products, and high-fat foods like salad dressings and peanut butter, can present problems. Meat scraps and the rest will decompose eventually, but will smell bad and attract pests. Egg shells are a wonderful addition, but decompose slowly, so should be crushed. All additions to the compost pile will decompose more quickly if they are chopped up some before adding.

To collect your kitchen waste, you can keep a small compost pail in the kitchen to bring to the pile every few days. Keep a lid on the container to discourage insects. When you add kitchen scraps to the compost pile, cover them with about 8" of brown material to reduce visits by flies or critters.

Wood Ashes from a wood burning stove or fireplace can be added to the compost pile. Ashes are alkaline, so add no more than 2 gallon-sized buckets-full to a pile with 3'x3'x3' dimensions. They are especially high in potassium. Don't use coal ashes, as they usually contain large amounts of sulfur and iron that can injure your plants. Used charcoal briquettes don't decay much at all, so it's best not to use them.

Garden Refuse should make the trip to the pile. All of the spent plants, thinned seedlings, and deadheaded flowers can be included. Most weeds and weed seeds are killed when the pile reaches an internal temperature above 130 degrees, but some may survive. To avoid problems don't compost weeds with persistent root systems, and weeds that are going to seed.

Spoiled Hay or Straw makes an excellent carbon base for a compost pile, especially in a place where few leaves are available. Hay contains more nitrogen than straw. They may contain weed seeds, so the pile must have a high interior temperature. The straw's little tubes will also keep the pile breathing.

Manure is one of the finest materials you can add to any compost pile. It contains large amounts of both nitrogen and beneficial microbes. Manure for composting can come from bats, sheep, ducks, pigs, goats, cows, pigeons, and any other vegetarian animal. As a rule of thumb, you should avoid manure from carnivores, as it can contain dangerous pathogens. Most manures are considered "hot" when fresh, meaning it is so rich in nutrients that it can burn the tender roots of young plants or overheat a compost pile, killing off earthworms and friendly bacteria. If left to age a little, however, these materials are fine to use.

Manure is easier to transport and safer to use if it is rotted, aged, or composted before it's used. Layer manure with carbon-rich brown materials such as straw or leaves to keep your pile in balance.

Seaweed is an excellent source of nutrient-rich composting material. Use the hose to wash off the salt before sending it to the compost pile.

The list of organic materials which can be added to the compost pile is long. There are industrial and commercial waste products you may have access to in abundance. The following is a partial list: corncobs, cotton waste, restaurant or farmer's market scraps, grapevine waste, sawdust, greensand, hair, hoof and horn meal, hops, peanut shells, paper and cardboard, rock dust, sawdust, feathers, cottonseed meal, blood meal, bone meal, citrus wastes, coffee, alfalfa, and ground seashells.

Lists of common composting materials can be found here.

6. Troubleshooting

Making compost is really quite easy, but having too much of a certain material or letting the compost get too wet or too dry can cause problems.

This table shows how to troubleshoot composting problems.