Everything You Need To Start Composting
First of all, let’s get this out of the way: You may not know it, but you already compost. The food waste in your garbage, the bits of tissue and cotton and hair in your bathroom trash bin, the bags of leaves you rake and gather every fall—all of that decomposes without human intervention.
But gardeners can step in and speed up the composting process by creating the optimal conditions for decomposition, which comes down to making sure your compost pile has the right balance of air, water, carbon and nitrogen. Put those things together, and you’ll get compost.
In honor of International Compost Awareness Week (ICAW), which runs May 7-13 2017, we’ve pulled together everything you need to turn your kitchen and yard waste into garden soil.
Why Make Your Own Compost?
Compost is simply decomposed organic matter, but it’s the best gift you can give your garden. Here are just a few of the many benefits of compost.
Compost encourages the formation of soil clusters that soak up water and hold it like a sponge, making your soil more resilient in times of drought. Adding compost to soil creates air pockets between soil clusters, improving soil aeration. Soil that contains lots of humus (compost) resists erosion from wind and water.
Compost also acts as a nutrient storehouse, gradually releasing nutrients to plants throughout the growing season. It even protects against disease: A thin layer of compost spread over the soil’s surface will fight plant diseases better than any chemical fungicide.
Finally, composting makes use of grass clippings, leaves, and kitchen scraps that otherwise would take up space in a landfill.
The Elements of Compost
Like most living things, the bacteria that decompose organic matter, and the other creatures that make up the compost ecosystem, need air. Compost scientists say compost piles need porosity—the ability for air to move into the pile. It helps to think of porosity in terms of fluffiness. A fluffy pile has plenty of spaces—or pores—for air to move about. A flat, matted pile of, say, grass clippings does not. Even fluffy piles compress during the composting process. Occasionally turning your pile refluffs the material, moves new material into the center, and helps improve air flow into the pile.
Compost microbes also need the right amount of water. Too much moisture reduces airflow, causes temperatures to fall, and can make the pile smell; too little water slows decomposition and prevents the pile from heating. Conventional wisdom says that compost should feel like a wrung-out sponge.
The microbes that break down organic matter use carbon as an energy source. Ingredients with a high percentage of carbon are usually dry and brown or yellow in color. The most common high-carbon ingredients are leaves, straw, and corn stalks. Sometimes people call these ingredients browns.
Microbes need nitrogen for the proteins that build their tiny bodies. Ingredients high in nitrogen are generally green, moist plant matter, such as leaves, or an animal by-product, such as manure. These ingredients are called greens, but in reality they can be green, brown, and all colors in between.
In order for a compost pile to decompose efficiently, you need to create the right ratio of carbon (C) to nitrogen (N) (C/N). Piles with too much nitrogen tend to smell, because the excess nitrogen converts into an ammonia gas. Carbon-rich piles break down slowly because there's not enough nitrogen for the microbe population to expand. An ideal compost pile should have a 30:1 C/N ratio. Grass clippings alone have about a 20:1 C/N ratio. Adding one part grass clippings, or other green, to two parts dead leaves, or other brown, will give you the right mix.
There are two main ways to make compost outdoors: cold compost (minimum effort) and hot compost (maximum effort).
This is the easiest type of composting if you have a back yard. Here’s how to make cold compost: Mix together yard wastes, such as grass clippings, leaves, and weeds, place them in a pile, and wait 6 to 24 months for the microorganisms, earthworms, and insects to break down the material. Add new materials to the top of the pile. You can reduce the waiting period by occasionally turning the pile and monitoring and adjusting the pile’s moisture level. The compost will be ready when the original ingredients are unrecognizable. Generally, compost on the bottom of the pile “finishes” first. You may not want to include woody material, because it breaks down too slowly.
Pros: Takes little effort to build and maintain; can be built over time.
Cons: Takes up to 2 years to produce finished compost; doesn’t kill pathogens and weed seeds; undecomposed pieces may need to be screened out.
Hot, or fast, composting takes more work and the right combination of ingredients, but you can get high-quality compost in under 2 months. Here’s how: Wait until you have enough material to create compost critical mass (27 cubic feet), which is the minimum volume for a pile to hold heat. Then mix one part green matter with two parts brown matter. Bury any vegetative food scraps in the center to avoid attracting animals. Check to make sure the mixture has the ideal moisture level. Continue adding mixed greens and browns and checking the moisture until you’ve built a pile that is 3 feet by 3 feet by 3 feet, or 5 feet wide at the base and 3 feet wide at the top. The microorganisms will immediately start decomposing, and their bodies will release heat. The pile will insulate the heat, and the temperature of the pile’s interior will reach 120°F to 150°F. Turn the pile weekly and regulate moisture levels. After about a month, the hot phase will be done, and the pile will finish decomposing at temperatures between 80°F and 110°F. The compost will be ready to use when it no longer heats and all of the original ingredients are unrecognizable.
Pros: Produces high-quality compost within 2 months (and sometimes as soon as a few weeks); can kill weed seeds and pathogens.
Cons: Time-consuming; requires careful management of moisture, air, and C/N ratio.
There are other ways to compost, even without access to green space. Here are two popular indoor composting methods.
This Japanese method uses microorganisms to ferment food waste. Collect your scraps in a compost bin, sprinkle them with an inoculated starter (available in starter bokashi composting kits), and let those little bugs do their thing for 7 to 10 days (you’ll have to drain off any liquid that develops). The final step is burying the fermented waste in the ground to complete the process. You don’t need much green space, but you do need some.
Pros: You can use bokashi for meat and dairy, unlike other forms of composting, and fans say the smell is minimal. It’s also a faster system than conventional composting, taking roughly half the time to produce valuable fertilizer.
Cons: If you have no outdoor space, this won’t work for you. However, you can try using a decently sized potted plant to finish your compost.
Common kitchen waste can be composted year-round in an indoor worm bin. The process requires red wiggler worms (Eisenia foetida). Unlike regular garden earthworms, which burrow in the soil, red wiggler worms act as nature’s recyclers, living on or near the surface, where they help decompose organic matter. This habit makes them ideal candidates for living in an enclosed worm bin. As they eat, worms produce castings—a crumbly, granular organic matter that is rich in nutrients.
Pros: Vermicompost contains a greater diversity of beneficial microbes than traditional compost, and it is linked with increasing plants’ resistance to fungal diseases. The nutrients in worm compost are also more available to plants—a quality that researchers think helps plants grow faster and stronger and resist attacks from aphids, mealybugs, and spider mites.
Cons: You need to avoid adding food or food with sauces, oils, or spices, dairy, and meat products. Citrus peels in large quantities may harm worms if they cause the bedding to become too acidic.