What is compost?

Compost  is a dark, crumbly, earthy-smelling material produced by the natural decomposition of organic materials like leaves, garden trimmings, and food scraps. During the composting process, bacteria, fungi, and other microbes feed on the organic materials. These beneficial microbes use carbon and nitrogen to grow and reproduce in the composting pile. Compost is a living soil amendment!

Why compost?

Compost improves soil, protects the climate, and builds community resilience. And almost anyone can do it! 

A mature, stable, good quality compost will enhance soil’s biological, chemical, and physical properties. Compost increases microbial activity, suppresses plant disease, improves the soil’s cation exchange capacity (enabling the soil to better hold on to essential nutrients), improves soil structure, increases water retention, and enhances soil fertility. Compost reduces the need for chemical fertilizers and pesticides. Another benefit: composting protects the climate! When rotting materials like wet food scraps end up in a landfill, they contribute to landfill emissions of methane (a greenhouse gas 84 times more potent than carbon dioxide in the short term!). But when those same food scraps are converted into compost and added to soil, they expand the soil’s ability to store carbon. Compost is rich in organic matter. Organic matter in soil acts as a carbon sink. By improving plant growth, compost also increases carbon sequestration.

Composting is an activity that you can do at home. It’s also an activity that can engage the whole family.

What are my options for composting at home?

Composting is nature’s way of recycling and it can happen without any involvement from us. You can speed up and optimize the process with a little attention to aeration, mixing, moisture, and pile building.

There are different ways to compost including worm composting (inside or outside) and outside composting (hot, which is a more active intentional process, or cold, which is a more passive process).

No matter what composting process you choose, ultimately your aim is to produce an amendment that is beneficial to the soil. If you don’t have your own garden or yard, consider reaching out to a friend or a local community garden about donating your finished compost.

Is it possible to compost if you don’t have access to an outdoor space?

Yes! Worm composting or vermicomposting can be done indoors. The process is completely different than traditional composting outside. There are 9000 species of earth worms but only 7 that eat food scraps. You must use the right species. In the United States, eisenia fetida worms are the most commonly used for vermicomposting.  

One great reliable source of information on vermicomposting is:
North Carolina State Extension’s Vermicomposting for Households 

How is vermicomposting different from traditional composting?

A vermicomposting system handles fewer types of food scraps. For instance, worms don’t like garlic and onion scraps, and citrus is not recommended. Eisenia fetida worms feed on the surface so the amount of food scraps that you can recycle in a worm bin is limited by not only the system’s surface area but also by how many worms are in the bin. One pound of worms equals approximately 1,000 worms. Worms eat about 25 percent of their weight each day. So if you start with one pound of worms, you can only feed your bin ¼ pound of food scraps. Fortunately, worms reproduce quickly. You can start harvesting vermicompost in a month and it doesn’t need to cure; it can be used immediately. Other benefits of vermicomposting are that you don’t need as large a supply of carbon-rich materials like fall leaves and there’s no mixing or aerating involved. 

What do I need to start outdoor composting if I’ve never done it before? 

You need: (1) a compost bin of some sort (we don’t recommend open piles for food scraps in suburban or urban communities), (2) space for the bin, (3) a pitch fork, (4) source of water, and (5) ready supply of leaves, twigs, straw, or other carbon-rich material (which you will need to mix with your food scraps). (More on composting “ingredients” below!)

Note: worm composting is different as noted above; these directions are for traditional composting.

If you’re in a dense urban area, we recommend your system be fully enclosed. There are many options readily available and also DIY designs (search online for “DIY compost bin”). Some cities have posted good DIY designs on their home composting websites; see, for instance, Oregon Metro’s 3-bin DIY design. Even systems made from repurposed materials such as old wooden pallets can be covered in ¼-inch hardware cloth to prevent unwanted critters from getting in. A bin that can hold at least 3 ft x 3 ft x 3 ft of material is ideal to help the pile heat up. Off-the-ground tumblers are good in urban areas. Stationary systems like the FreeGarden™ Earth and the Earth Machine can also work in densely populated areas; we recommend buying the base for these or making your own out of ¼-inch hardware cloth staked to the ground underneath the bin. Read reviews to learn about ease of assembling and other characteristics.

The most important tool for home composting is a pitchfork! If you’ve already got one, great. If not, procure a manure or compost fork, which has a scooped profile and tines that are rounder, thinner and more pointed than a typical garden digging pitchfork. 


A note about buying local:

Please support your local hardware store! Many are still open during the COVID-19 pandemic or can deliver an online purchase. ILSR actively supports independent locally owned businesses and fights corporate monopolies like Amazon.


Photo credit: A two-bin system in Seattle that can be used for backyard or community-scale composting. Source: Tilth Alliance

The basic ingredients for composting are: 

  • GREENS – Nitrogen-rich materials that are relatively high in nitrogen such as raw vegetable and food scraps, grass clippings, and green leaves. Coffee grounds, even though brown in color, are rich in nitrogen.
  • BROWNS – Carbon-rich materials that are relatively high in carbon such as fall leaves, twigs, shredded newspaper, straw, wood chips, and shredded wood.
  • WATER
  • AIR

The composting microbes need nitrogen to grow and reproduce, and carbon for carbohydrates and  energy. They need water to move around and digest materials and, just like us, they need oxygen to breathe.

Make the microbes happy by giving them a balanced diet of carbon to nitrogen materials. One rule of thumb is to mix 2 to 3 parts of brown materials to 1 part of green materials by volume. So if you have a bucket of food scraps, you will need 2 to 3 buckets of browns such as fall leaves.

How much water do I need to compost properly?

The initial compost pile should have a moisture content of 50 to 60 percent. This is more than most people realize! If the pile is too dry, microbial activity will slow or cease. If it’s too wet, water will fill in air pockets the microbes need to live, and smelly, anaerobic (lacking oxygen) conditions will take over. To make sure that you have enough water in your compost pile, try the “hand squeeze” moisture test. Some moisture will come from your food scraps, but if more moisture is needed, water as you mix and build your pile. 

What materials can I compost in my outside bin?

If you’re new to composting, we recommend starting with fresh vegetable and fruit scraps as your greens. Do not include any meat, dairy, greasy/oily, or cooked foods. Rodents are attracted to proteins and greasy or oily foods can create odors. Also avoid putting diseased plants in your pile. Egg shells are fine but crush them first!

Do I need to chop materials before adding to the compost pile?

Chopping is not required but will help materials break down faster in the pile. Consider chopping corn cobs, pineapple tops, broccoli stalks and other tough food scraps. Do NOT try to cut avocado or mango pits! They will eventually break down. Do cut yard trimmings like vines and long stalks. Materials in the 2 to 6 inch range will compost more quickly. Anything that doesn’t break down can be screened out and reintroduced to the active pile.

Do I need to turn my pile?

You do not need to turn or remix your pile but doing so will speed up the composting process. If you don’t turn, it can take up to a year to have finished compost. With some more attention and regular pile turning, you can have finished compost to add to your garden beds in 2 to 5 months. Remember, composting is an aerobic process, meaning it requires air and oxygen! 

What role does temperature play in the composting process?

Hot, or thermophilic, composting requires more attention than cold composting. Cold composting refers to piling of materials with little attention to the ratio of browns to greens, moisture, or turning. It is different from worm composting, or vermicomposting; when vermicomposting, you don’t want your bin to heat up!

Regardless of what option suits you, never leave food scraps exposed on top of a pile; always cover with 4 to 8 inches of carbon-rich material like wood chips, mulch, fall leaves, or even finished compost.      

To achieve hot composting, turn or remix your compost pile, water as needed, and generally attend to it fairly regularly. Hot composting has two main benefits over cold composting:

  • It’s a quicker process. You will have finished compost in 3 to 5 months as opposed to a year or more with cold composting.
  • The temperatures reached in hot composting help to reduce the presence of pathogens and weed seeds. 

While you do not need a temperature probe to compost outside, it can be very helpful to monitor what is going on in your pile. Reotemp is one source of backyard composting probes. Steady composting takes place in the 80 to 130°F range and hot active composting between 130 to 160°F. Tomato seeds are often the most difficult to prevent from germinating. The pile needs to reach about 154°F for 3 days straight to prevent tomato seeds from sprouting.

The Phases of the Hot Composting Process
Illustration adapted with permission from Nancy Trautman and Marianne Krasny’s Composting in the Classroom: Scientific Inquiry for High School Students (1997).

Ten Steps to Starting & Maintaining a Home Composting System

  1. Decide on a kitchen pail that you will use to collect food scraps in your kitchen.
  2. Locate your composting bin. You want a spot that has good drainage, is convenient to the kitchen, and provides you 3 feet of clearance around the system. Do not put right up against a fence! Rodents, for instance, love clutter and hiding spaces. Best to place your bin in an open area. A shady location with easy access to a water supply is ideal.
  3. Set up a storage system for browns near your composting bin. This makes it easy to mix in browns with food scraps when adding to your system. Unlike food scraps, browns can be stored outside.
  4. Have your tools accessible. Helpful tools include a pitch fork, a watering can or hose, buckets for mixing, a backyard compost thermometer (if you want to track temperatures), and a scale (if you want to measure your impact!).
  5. Create a 4- to 6-inch base of bulky browns, such as twigs or wood chips, in the bottom of the composting bin. This layer of browns will help absorb extra liquids and keep air circulating.
  6. Build a pile. This can be done by either layering browns and greens in the “lasagna” method, or adding greens to a big pile of browns. Remember, you want at least two to three times the volume of browns to greens. If needed, add water as you add materials to your pile.
  7. Aerate and mix as needed (e.g., aim for weekly for first few weeks, or based on temperature or odor).
  8. Check and adjust moisture levels as needed. Remember the hand-squeeze test!
  9. After 8 to 12 weeks, harvest the oldest compost from your composting bin (it should be dark and crumbly, with no visible food scraps). If you’re not using the compost right away, consider placing it in a “curing” pile to finish for another 4 weeks.
  10. Screen or sift your compost (optional) and add to your garden! (You can make a home-made screener out of ¼-inch hardware cloth to sift out pieces of twigs and pits that have not broken down. Remove contaminants like produce stickers, twist ties, and plastic, then introduce the screened-out materials, known as “overs,” back into the active compost pile.

Be safe!

Follow basic health and safety hygiene. Consider wearing gloves when handling compost or raw materials. Either way, be careful with hand-to-mouth contact and wash your hands after composting, especially before eating. Treat cuts and scrapes immediately and protect wounds by covering them appropriately. Consider wearing a mask or other face covering for dry, dusty conditions and if you have asthma, other respiratory issues, or cystic fibrosis (N95 masks are recommended, but any face covering is better than none). Masks protect against airborne bioaerosols such as aspergillus fumigatus, a species of fungus that lives in soil, decaying leaves, and compost, and that can produce airborne spores. 

DIY & Reusable Masks Resources

Compost Troubleshooting

How do I know when my compost is ready to use?

When your compost pile no longer heats up after mixing and there are no more visible food scraps, allow it to cure, or finish, for at least 4 weeks before using the compost. You will either want to remove the oldest compost from your composting system to a separate curing pile, or just stop adding to your composting system altogether so that your entire compost pile can cure. At the end of the curing process, the materials you added to your composting system will have shrunk to about one-third of their original volume and the compost should be mature and ready to use. Characteristics of mature compost include:

  • Crumbly, loose, and humus-like structure
  • Dark brown color
  • Earthy smell
Test Your Compost at Home:
  1. Compost respiration test (tests compost maturity): Add a handful of moist compost to a ziplock bag, press out air and seal. Store out of the sun for 3 days, open and smell. The smell of ammonia means it needs to compost longer.
  2. Seed germination test (tests compost quality): Put a handful of your compost on a plate & moisten it. Count 100 seeds from a new seed packet and add them to the compost sample. Keep your compost moist and warm. In a few days, compare the number of seed sprouts to the germination rate on the seed packet (or look it up online). Good germination, likely means good compost.

 

Using finished compost in the garden*

Soil Incorporation

Mix compost into a garden bed prior to seeding or transplanting. Add a 2- to 4-inch layer to the surface of the soil and mix into the top 6 to 8 inches of soil. The compost should be fully mature.

Mulch

Adding a layer of compost as mulch incorporates nutrients more slowly, but is still beneficial. This is a use for compost that is not fully mature. Mixing unfinished compost into soil removes nitrogen and starves plants. Pull up sod around desired plants and loosen the top 2 to 3 inches of soil. Add mulch in a 3-inch layer on the soil surface, 2 to 3 inches away from plant stems or tree trunks.

Potting Mix (for seedlings in small containers)
  1. Sift compost through ½ inch mesh
  2. Mix two parts compost, one part coarse sand, and one part loamy soil or coconut coir
  3. Add ½ cup garden lime (pulverized limestone) per 8 gallons potting mix
*Sources: New York City Master Composter Course Manual (2015) &
Cornell Waste Management Institute’s Master Composter Resource Manual (1998)