Composting Kitchen and Yard Waste

Mar 02, 2010 | Waste Management

Snapshot | Composting basics | How to choose | What to do with compost

Snapshot

Don't throw away kitchen and yard wastes-compost them! Composting is a natural decomposition process that turns these organic wastes into a rich soil additive called "humus" that is great for your garden, your landscape shrubs, and your lawn. If you are a city dweller with no yard, you can apply compost to your potted plants and even your sidewalk plantings.

Compost diverts organic waste from landfills, where it takes up space and combines to create methane, a natural gas containing more than 20 times the carbon of most carbon emissions, contributing to climate change.

Yard trimmings and food residuals together constitute 26 percent of the U.S. municipal solid waste stream. That's a lot of organics that could be returned to the soil to support plant growth.

Adding compost to plants feeds them nutrients, helps them retain water, and improves their ability to fight plant diseases.

Some composting methods are just piling wastes and turning them periodically. Others involve plastic containers or enclosures made of wood or wire mesh. What these composting methods have in common is air.

Composting basics

Composting is aerobic decomposition, which means it's a process that uses oxygen. Contrast that to anaerobic decomposition-commonly known as "rot"-which occurs with little air and produces a gas called methane, which can be smelly.

In addition to these oxygen-using bacteria, the process works with the help of fungi, nematodes, and even ants, pill bugs, and worms.

What you need to know is how to manage the process factors that make composting happen:

Air: Composting is typically done by making a pile or providing a perforated enclosure that allows in air. That's because composting is an aerobic process that needs oxygen. Other methods are turning, tumbling, or batching it. Turn it every one or two months or so with a shovel or spading fork. But don't turn it too often or you will release some of the heat that helps speed the process!

Tumbling can be done in an enclosed container composter you buy or make out of a barrel. Batching is the easiest: Simply create two or three composting piles or composters, not just one. As one fills, start another. By the time the second and third are full, the first might be full of finished composted unmixed with fresher inputs.

Moisture: Simply put, the contents of your composter should have the moisture content of a well-wrung sponge: somewhat wet but not so much that it leaves your hand glistening when you touch it. Any wetter than that, and some of the composting microbes might drown and odors can result. That's because the composting microbes live in a film of water.

Heat: The warmer the process, the faster composting occurs. That's why composting happens faster in the spring and summer than the winter. Below 41°F, most biological processes slow to nearly zero. The composting process heats up as the microbes eat and give off heat. This heat can kill weed seeds and plant diseases as well as some pathogens. Your compost won't exceed 140°F (and it rarely gets that hot unless you are managing it diligently), but you might see it steaming on cold mornings!

Carbon-to-nitrogen ratio (browns to greens): This can be confusing for some. Essentially, compost microbes need carbon (carbohydrates) and nitrogen (protein) just like humans do. Just like us, they need a ratio of about 4 parts carbon-sometimes referred to as "browns" because many carbon sources are brown, such as leaves, old grass clippings, and woodchips-to 1 part nitrogen or "greens" which refer to the green color of fresh grass clippings, newly fallen leaves, and vegetable and fruit parings from the kitchen. See this chart for examples of carbon (browns) and nitrogen (greens) sources:

The good news is that composting isn't precise chemistry. The 4-to-1 parts carbon-to-nitrogen ratio is a general guideline. If your composter is composting slower than other people's, consider whether it needs more moisture, more carbon, or, most likely, more nitrogen.

It's easy to make a composter out of discarded wood pallets. Staple on chicken wire or metal mesh to keep out squirrels and rodents. Photo: WattzOn A tumbling composter aerates its contents. Photo: WattzOn Manufactured composters abound. Many towns offer low-cost composters to allow their residents to divert organics from the waste stream. How to choose

There are many ways to compost:

Piles: An easy way to compost if you have a lot of room is simply to create piles. Remember that 3 3-foot-high piles get more air to the composting microbes than 1 9-foot-high pile. Turn the piles periodically with a shovel or spading fork. This method works best when you have a lot of grass or leaf clippings. Bury food scraps in the center of the pile where it's more biologically active and away from squirrels and other animals.

Wood and wire bins: You can make an inexpensive composter with wood, discarded wood pallets, and chicken hire and mesh fencing. You can even use 3- and 4-foot-high picket fencing to create an attractive backyard composter. When making one bin, consider making 1 or 2 more so you can start new piles. When the third bin is full, the first bin should be full of finished compost you can shovel out and trench around plants.

Plastic and manufactured composters: You can buy a manufactured plastic composter from your hardware store, an online store, and sometimes from your municipality. Many towns offer lower-cost subsidized composters to promote diverting organic scraps from the trash stream. These are designed to work in a small space and to deter animals (although eager animals might find a way in). Some are round and designed to be rolled to turn their contents. You can also make your own composter by drilling half-inch holes in a garbage can with a lid. Be sure to perforate the bottom of the can liberally.

Other composting options: Specialized composters are available for use inside the home. They include worm composters you can put under the sink or just outside the door, small electrically heated and vented composters that can reside in your basement, and small cone-like composters inserted into the soil and used to compost pet droppings and kitchen scraps.

Collecting kitchen scraps is as easy as putting these scraps in a small colander or bowl next to the sink. You can also use plastic bags made of biodegradable cellulose or cornstarch. If you can't get them to your composter right away, put them in the freezer. Several attractive countertop receptacles designed to hold compostables are also available. Some even have built-in charcoal filters to minimize potential odors.

Composting tips

• Eggshells are great sources of phosphorus for your plants. Crush them with your hand (or put them in paper bag and crush them) and put them in the composter.

• If your composter isn't getting enough moisture, hose it in, open it to rainwater, or add waste liquids-such as bits of soup, juice, and coffee-and soggy kitchen wastes (watermelon rinds, etc.) to boost the moisture.

• You can add shellfish shells, bones, and other items that won't compost fast or at all. You likely will have to rake them out later.

What to do with compost

When compost is ready to use, it looks like a chunky, fibrous dark soil. Its chunkiness adds structure to soil, helping roots grow and creating spaces to store water. However, if it isn't fine enough for your purposes or contains too many twigs, rocks, twist ties, or other items that can make their way into your composter, sift them out by shoveling it onto a piece of wire mesh suspended over a wheelbarrow or attached to a wood frame.

After removing compost from the composter, some let it further compost in the sun by spreading it on the ground. Do this or trench it directly around plants. It will continue to transform while aiding plants.

Don't be intimidated by composting. There's little you can do that can't be corrected by adding water or more carbon materials or turning it. Composting is a great way to create a valuable product from what could have been garbage. It's win-win all around.

Your kitchen food scraps and yard wastes can be converted to a rich soil-like compost. Don't trash it!

Carbon sources or "browns" for the compost pile Fall leaves Pine needles Twigs, chipped tree branches/bark Straw or hay Sawdust Cornstalks Paper (newspaper, writing and printing paper, paper plates and napkins, coffee filters, and even used paper towels) Dryer lint Cotton fabric Corrugated cardboard (without any waxy or slick coated paper coatings

Nitrogen or "greens" for the compost pile

Grass clippings Coffee grounds/tea bags Vegetable and fruit scraps Trimmings from perennial and annual plants Annual weeds that haven't set seed Eggshells Animal manures (but no dog and cat excreta) Seaweed