What is Composting?
Composting is the process of creating the ideal conditions for the rapid decomposition of organic materials. You can think of composting as speeding up the way nature recycles. In nature, when a leaf falls to the forest floor, it is consumed and digested by a host of creatures, from worms and insects to microorganisms such as bacteria and fungi.
When we make a compost pile out of our organic materials, we are creating the conditions that decomposer organisms need to thrive. Only organic materials can be composted—and to prevent disease and odors, certain organic materials, such as animal products, shouldn’t be included in home compost bins (see below a list of what to compost).
When the decomposer organisms have done their job, what starts out as fruit and vegetable scraps—which would have wound up in your garbage can—becomes a nutrient-rich material called compost, a dark, crumbly material that looks and feels like soil.
Adding compost to soil is an excellent way to improve soil texture: it loosens heavy clay soils, making them better for root growth, and it helps light, sandy soils retain water and nutrients. Compost suppresses diseases, provides vital aeration to plant roots, and is a source of minerals and nutrients that are essential to plant growth and health.
Food scraps and yard trimmings together make up almost 1/3 of NYC’s residential waste stream. That’s a lot of waste to send to landfills when it could become useful and environmentally beneficial compost instead!
1. Set Up Your Bin
Compost bins are really just containers for your compost pile that serve to keep warmth and moisture in, and keep pets, rodents, and other pests out. They also help keep your pile sightly, tidy, and compact, which can be especially important in small yards. People set up compost bins on terraces, roof gardens, patios, next to outdoor garbage cans, in courtyards, side alleys, and community gardens.
Choose a compost bin based on the space you have available for composting, the materials you want to compost, your budget, and the amount of time you want to spend tending your pile. Visit nyc.gov/compostproject to find out about the NYC Compost Project or to obtain more information about buying or building a compost bin.
Holding units are the simplest types of bins but shouldn’t be used for food scraps because they lack adequate protection against rodents. Therefore, holding units should only be used for composting leaves and garden trimmings. You can construct your own using inexpensive or recycled wood, chicken wire, or cinder blocks. Simply add the appropriate organic materials to your holding bin and let the material decompose. This method requires little work, but can take from six months to a year to make finished compost. If you want to regularly;add additional leaves and garden trimmings, you will need to either speed up the decomposition process or add more than one holding unit.
Enclosed bins are suited to handle both yard trimmings and kitchen scraps. They are most appropriate for small yards or any small space, such as a side alley, roof garden, or terrace. If you live in a multi-unit building and are placing your compost bin near
outdoor garbage and recycling cans, make sure you visibly label your compost bin so that other residents do not accidentally place refuse or recyclables in it. Other options used in New York City include installing a combination lock for the compost bin. You can construct an enclosed bin by drilling ventilation and drainage holes in the lid, sides, and bottom of a 20- or 30-gallon garbage can or barrel.
Rodent-proofing should not be necessary if your compost bin is enclosed. However, if rats are a problem in your area, you can take additional steps to make your bin more rodent resistant:
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Should I set up my compost bin in a sunny or shady spot? Should I set up my compost bin on pavement or soil? |
2. Add Organic Materials (Food and Garden Waste)
To know what to add to your compost bin, it is helpful to classify organic materials into “greens” and “browns”.
Greens are fresh, moist, nitrogen-rich plant materials that still have some life in them (fruit and vegetable scraps, coffee grounds, tea bags, fresh leaves, yard prunings, grass clippings, etc.).
Browns are dry, carbon-rich plant materials with no life in them (fall leaves, shredded paper, straw, wood chips, twigs, etc.).
If you are primarily composting “browns," shredding items such as leaves into smaller pieces and keeping the pile moist will speed up the decomposition process.
When composting “greens,” such as food waste or green garden trimmings, be sure to start with a layer of browns. Maintain equal amounts of greens and browns throughout the bin for successful composting. Always cover food scraps with a layer of browns to deter pests and flies. If you have space for bagged leaves, keep a supply near your compost bin throughout the year to cover food scraps. A convenient way to store kitchen scraps (before adding them to your compost pile) is to keep them in the refrigerator or freezer inside a resealable container or large zip-lock bag.
Here are materials that are excellent for composting. Aim to add equal amounts of “greens” and “browns”, but when in doubt, it’s better to err on the side of adding more browns.
GREENS (fresh, moist, nitrogen-rich materials)
FROM YOUR GARDEN
• green plants and garden trimmings
• fresh leaves and flowers
• grass clippings (or recycle by leaving on the lawn)
FROM YOUR KITCHEN/HOME
• fruit and vegetable scraps
• coffee grounds and tea bags
• manure and bedding from animals that ONLY eat plants
BROWNS (dead, dry, carbon-rich materials)
FROM YOUR GARDEN
• fall leaves, small twigs, and woody prunings
• dry plant material
• straw and hay
• pine needles
• potting soil
FROM YOUR KITCHEN/HOME
• bread and grains
• egg shells
• nutshells
• corncobs
• food-soiled paper towels and napkins
• shredded newspaper
• sawdust and wood shavings (from untreated wood)
• stale beans, flour, and spices
• wood ashes
… and what to avoid
FROM YOUR GARDEN
• pesticide-treated plants or pesticide-treated grass clippings
• diseased or pest-infested plants
• poison ivy
• invasive weeds
• weeds with seeds
• large branches (call 311 to schedule a special removal)
• non-compostable materials such as sand or construction debris
FROM YOUR KITCHEN/HOME
• meat or fish scraps
• cheese or dairy products
• fats, grease, or oil
• cat or dog feces; kitty litter
• colored or glossy paper
• sawdust made from pressure-treated plywood or lumber
• coal or charcoal ashes
• non-compostable materials such as plastics, metals, or glass
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Do I need to add worms to my compost bin? Do I need to add a bioactivator? |
3. Check Moisture
The ideal moisture level for your compost bin is like a wrung-out sponge: moist, but not soggy. If composting food waste, the “greens” will provide the needed moisture, and the “browns” will soak up some of this moisture and distribute it evenly throughout the bin. If you are mainly composting yard waste (and therefore you have an abundance of “browns”), you may need to add water. When adding water, make sure to turn the pile as you spray to evenly coat and soak the material. Leaves should glisten with moisture. Shredded paper should be wet, but not “mushy.” During the hot summer months, you may need to add extra water.
It is essential to monitor moisture levels so that your compost pile remains moist and never dries out.
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Can I compost year round? What should I do if my compost bin becomes soggy? How often should I turn my compost pile? |
4. Turn the Compost Pile
In order for the microorganisms in your pile to do their work, they need just the right combination of greens, browns, moisture, and air. Steps 2 & 3 address the first three components, so let’s look at how you can get air into your compost pile.
From time to time, you should turn or aerate your compost. Take a long-handled rake, pitchfork, compost crank, or even a long stick and push it down into different parts of the pile to mix and “fluff” up the compost. Try moving the inside of the pile outward and the outer areas to the inside.
5. Check the Compost
As you continue to add and mix organic materials, check on the compost to make sure there is adequate moisture, and periodically turn the pile.
At a microscopic level, bacteria and fungi eat and digest decaying organic matter. Other important decomposers in the compost pile are larger creatures, such as beetles, centipedes, and worms. These macroorganisms work alongside the microscopic decomposers to consume the organic material in the compost pile.
The carbon (browns) and nitrogen (greens) in the compost pile provide these bacteria and decomposer organisms with necessary energy and cell-building ability.
As the microorganisms digest the material in a compost pile, they produce heat, carbon dioxide, and excrement. This is why some compost piles will heat up. The microorganisms convert organic materials into a stable humus, which has an earthy odor and provides texture and nutrients to improve soil quality.
The organisms responsible for decomposition are naturally present in the environment and will readily establish themselves in a compost pile. Left on its own, all organic matter will eventually decompose. However, moisture, oxygen, particle size, and the mix of materials you include in your compost pile will affect how rapidly your pile will decompose. Following the tips in this brochure should help you produce compost, while minimizing odor or pest problems.
Rotten-egg odor
Problem: Excess moisture and not enough air (anaerobic conditions).
Solution: Turn pile frequently; add dry material such as fall leaves,
woodchips, or shredded newspaper. Make sure bin has drainage; leave
lid off to allow more air to flow.
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Ammonia odor
Problem: Too much green, high-nitrogen material (such as food scraps, grass clippings).
Solution: Add brown, high-carbon material (such as fall leaves, woodchips, or straw).
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Slow decomposition
Problem: Lack of moisture, lack of air, or lack of nitrogen.
Solution: Add water as needed; turn pile, add aeration tubes; add material high in nitrogen, such as food scraps.
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Unwanted pests, flies
Problem: Wrong materials in the pile; food scraps are exposed; bin isn’t rodent resistant.
Solution: Don’t add animal or dairy products, grains, or fatty foods. Make sure food is well covered. Make bins more rodent resistant by adding hardware cloth to areas where animals could get through. Add a screening barrier vertically 6 to 8 inches into the ground. Keep the pile moist and turn pile more often to increase temperature and disturb nesting.
6. Use Your Compost
Finished compost resembles dark, crumbly topsoil and should bear no resemblance to the original materials. Compost should have a pleasant, earthy smell to it.
A quick test to see if your compost is finished: Place some of the compost in a sealed plastic bag. Wait a few days. If you open the bag and it does not smell, your compost is done. If it smells rotten, put it back—it’s not finished.
How to use compost
If you have ever bought and used peat moss, wood chips, manure, or topsoil, then you already know how to use compost. Mix compost into flower and vegetable beds; blend it with potting soil to revitalize indoor plants; or spread it on your lawn as a fertilizer. Use coarser compost as a mulch around trees and shrubs. If you prefer finer compost, you can screen it to sift out the bigger pieces. Do not place compost as mulch directly against tree trunks, as this will damage the tree.
Using “unfinished” or immature compost that contains food scraps can attract rodents or other vermin, so make sure this type of compost has fully decomposed before adding to your garden beds. Unfinished leaf compost can be mixed directly into flower or vegetable beds in late fall; the material will mature over the winter and be ready for spring plantings.
How much compost to use
Follow these guidelines to determine how much compost you need:
For amending soils… The specific amount of compost that soils need is a function of the nutrients that are lacking, the condition and the texture of the soil, and the types of plants you plan to grow. Testing your soil can help determine its condition and needs. In general, work 1 or 2 inches of compost into the top 3 to 5 inches of soil.
For flowers… In the spring, loosen the top few inches of annual and perennial beds and mix in a one-inch layer of compost. Or, in the fall, apply a one-inch layer of compost as a mulch to control weeds and conserve moisture.
For vegetables… Give your vegetable garden plenty of compost in the fall. Spread several inches of compost on top of the existing bed and you can till it in come springtime. Put a handful of compost in each hole when you’re planting.
Once plants begin to grow quickly, you can add a half-inch layer of compost around the base of the plants. Provide “heavy feeder” plants such as tomatoes, corn, and squash with half an inch of compost monthly—this will result in great produce! Note: If you make compost with plant cuttings or grass clippings that have been sprayed with pesticides, do not use the compost on edible crops.
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How long will it take to make finished compost? Can I use compost for potting soil? |
Potted plants and window boxes… Even the best potting soil gets depleted of its nutrients as plants grow in it. To replenish nutrients, add an inch of compost to potted plants and window boxes twice a year. Work it into the top layer of the existing soil, removing some of the existing soil to accommodate the additions if necessary.
Or, make your own potting soil using two parts screened compost to one part sand or perlite.
For lawn/turf…
You can also topdress existing turf with as much as one-half inch finely screened compost. This is easiest with a spreader, but you can use a shovel for small areas where you want to add compost. Rake the compost evenly throughout the grass area to enable the compost to readily sift down to the soil. The compost will settle down into the soil, improving its structure and providing nutrients. Over time, this will mean less compaction, fewer bald spots, and a reduced need for synthetic fertilizers.
Planting trees...
When planting a new tree, it’s best to work one-half inch to one inch compost into the top two inches of soil from the trunk of the tree out to the dripline—the outermost parameter of the tree’s canopy. Compost used in this way serves as a substitute for the layer of organic matter that naturally exists on the forest floor: it provides organic nutrients, reduces moisture loss, and keeps the soil cool. Don’t add compost to a freshly dug hole when planting a new tree, as applying compost in this way will discourage tree roots from going beyond the hole.
Tree and shrub maintenance… Apply compost as mulch to trees and shrubs to prevent weeds and make plants more drought resistant. Spread up to two inches of compost under the tree or shrub out to the drip line (the outermost leaves on a tree) or to the edge of the bed. This will help reduce moisture loss and stabilize soil temperature.
You can also incorporate compost into the soil once or twice a year to provide organic nutrients. Before adding compost to compacted soils, gently cultivate the soil with a hand tool; this will prevent damage to shallow feeder roots while making nutrients more readily accessible to the trees or shrubs.
Do not place compost or mulch directly against the bark of the tree or shrub or on exposed woody roots as this could cause rot and invite pests and disease.
The Department of Sanitation (DSNY) encourages residents to compost yard trimmings and food scraps in their own backyards and community gardens. This kind of composting is not only the least expensive way to manage organic waste, it also recycles nutrients close to where they can best be used to nourish our city’s soils.
The NYC Compost Project, created by DSNY in 1993, works to rebuild NYC’s soils by providing New Yorkers with the knowledge, skills, and opportunities they need to make and use compost locally. NYC Compost Project programs are implemented by DSNY-funded teams at seven host organizations, including Brooklyn Botanic Garden, Big Reuse, Earth Matter NY, Lower East Side Ecology Center, Queens Botanical Garden, Snug Harbor Cultural Center & Botanical Garden, and The New York Botanical Garden.
If you are interested in composting at home or in your community, the NYC Compost Project provides technical guidance on constructing composting systems and sells low-cost composting equipment. Each site also manages a compost help line to answer questions and to troubleshoot problems over the phone or by email.
