Not every gardener has the space for a large compost pile, and not all municipalities allow backyard composting. The good news is that it's very easy to compost in a small space. Even if all you have is a patio or balcony, you can use this easy method of making compost in a trash can. And, if you need to compost on the sly, no one will be the wiser; they'll just see another trash can.
How Composting Works
Composting can seem mysterious, but it is actually a relatively simple process. Compost is essentially just organic (carbon-based) material that has decomposed—broken down into simpler components under the action of helpful microorganisms, including bacteria and fungi. Any organic material will eventually break down on its own, but the gardener who maintains a compost bin helps speed up and enhance this process by deliberately combining the necessary ingredients—organic material, moisture, oxygen (air), and bacteria.
As organic materials break down into usable compost—a process that can take anywhere from three weeks to a year—the nutrients are "unlocked" into a form that living plants can use once more. Compost has many uses in the garden, as soil amendment, as an additive to potting soil, as mulch around trees and shrubs, or even as a top-dressing for lawns.
Two things you should never add to your composter are meat and dairy products, as they will spoil and smell, and are certain to attract pests. Nor should you ever add pet wastes to a compost bin. Any form of animal waste can introduce harmful pathogens that can cause illness. Although commercial compost often includes animal manure and other animal byproducts, this material is manufactured in a high-heat environment that kills off any pathogens. Garden compost bins often cannot generate the heat necessary to safely compost animal wastes.
What You'll Need
- Metal or plastic trash can with lid (32-gallons or larger)
- 2- or 3-inch hole saw
- Aluminum screen fabric
- Epoxy adhesive or silicone caulk
- Plant-based organic waste
- Nitrogen fertilizer or compost starter (optional)
Buy a Trash Can
Find or buy a 32-gallon or larger plastic or metal garbage can with a tightly closing lid. If rats or other animal pests are a problem in your area, a metal can is recommended.
Using a drill with a two- or three-inch hole saw, drill holes all the way around the trash can (lid, bottom, and sides), 6 to 12 inches apart. These holes will provide the airflow and oxygen necessary to enhance the composting process.
Cut pieces of metal window screening large enough to cover each hole. Cover each hole on the inside of the can with a patch of window screening, securing it with epoxy or silicone caulk.
Add Waste Material
Put your trash can composter in a convenient place. If possible, raise it up on a couple of bricks for air circulation below the can.
Now, you can begin adding plant-based organic materials to the composter. A trash can composter can accept anything you would put in a standard compost pile, including:
- Fruit and vegetable peels and cores
- Leftover cooked veggies (as long as they don't have salt or butter on them)
- Produce that's past its prime
- Coffee grounds
- Tea leaves and tea bags
- Shredded newspaper
- Weeds, leaves, and spent flowers from the garden
Most expert sources on composting recommend using specific ratios of "green" and "brown" materials to make perfect compost. You may be able to get away with ignoring ratios if you have a large pile, but in a closed system such as a trash can, paying attention to the ratios of your materials is important.
If you have too many "greens," such as fruit and veggie peels, weeds, and grass clippings, the pile will stay too wet and will start to smell. If you have too many "browns," such as leaves, small twigs, shredded paper, and coffee grounds, the pile will fail to generate the necessary heat and will decompose very slowly. Try for a ratio of at least 4:1 of browns to greens. You may see recommended ratios as high as 25:1, but the 4:1 ratio works well in a trash can composter.
It is a good idea to add a shovelful of garden soil to your compost. The soil contains all kinds of microorganisms that will consume the contents of your compost and break it down. If you don't have access to garden soil, don't worry. You'll still get compost, but it will take a little longer.
To speed along the decomposition of organic materials, you can add a handful of nitrogen fertilizer, or a small amount of commercial compost starter. Compost starters include mixture of nitrogen and helpful microorganisms that jump-start the decomposition of organic material.
Monitor and Turn the Pile
In addition to a proper ratio of materials, you'll also need to make sure that your compost stays moist but not wet. In general, your compost should feel like a wrung-out sponge—slightly damp but not sopping. Any wetter than that, and it will start to smell because it has become anaerobic—meaning oxygen is not reaching parts of the pile. If your pile dries out, it will still break down eventually, but it will take much, much longer than it should. A pile that is too dry generally will not emit any warmth.
In addition to monitoring moisture, you'll also need to keep your compost aerated to provide oxygen. In a traditional pile, this is done by digging into the pile and turning the contents every week or two. You can aerate your trash can composter by simply laying it on its side and rolling it around a few times. Do this once or twice a week until the compost is ready to use.
Use the Compost
Your compost will be ready to use when it has reached a uniform, crumbly dark-brown texture and no longer emits any warmth. This indicates the material has broken down fully. At this point, it becomes "garden gold" that you can use in any number of ways, such as applying as a surface dressing to mulch around shrubs, trees, and other plants, or as a soil amendment to improve the texture and fertility of soil before planting.
A trash can full of organic material can be transformed into useable compost in as little as three weeks if it is monitored closely and turned regularly to add air. It is more typical, though, for the process to require about two months.
Tips for Composting
- Compost loses a lot of volume as the organic material breaks down. Up to a point, you can continue to add organic materials to the composter as the materials break down and the level in the trash can drops. But at some point, you should stop adding materials in order to allow the contents to fully "cook" and convert into useable compost. Many gardeners keep several compost bins in various stages of decomposition, so that they can harvest useable compost from one bin while others are in earlier stages of decomposition. Three or even four bins may be necessary for large landscapes where there is lots of available plant waste.
- Although weeds can be composted, their seeds may remain viable unless the compost bin generates enough heat to kill them. Many home compost bins do not develop the heat necessary to kill off all seeds. For this reason, some gardeners avoid putting weeds into the compost bin.
- Don't compost plant material that has clear signs of diseases, such as fungal leaf spots or viral or bacterial disease. Sometimes these pathogens will survive the composting process and can be spread around the garden as you use the compost.
- Sticks and twigs can be composted, too, although they take longer to break down. Some gardeners keep a dedicated compost bin for handling these coarser materials, mixing them with other finer-textured "green" materials and allowing a full year for the material to break down into useable compost. If you compost sticks and twigs, it helps to chop them up into small bits before adding them to the bin.
Composting Without Air?
The traditional composting method requires air in order to work. It is known as aerobic composting. But it is also possible to compost organic material anaerobically—without air. It is accomplished by simply confining organic material and moisture in an environment where there is no access to oxygen. This process uses an entirely different group of microorganisms, and it takes considerably longer, but in the end, it also produces nutritious compost.
Garbage cans with lids are perfect containers for this kind of composting, too. Instead of drilling plenty of air holes in the sides of the container, drill only a few drainage holes in the bottom. Then, keep the containers tightly sealed except when you are adding material. Such compost does generate odor, but this generally is not a problem since you'll be keeping the trash can tightly sealed. This is a method that works best if you have plenty of space for multiple trash cans.