By Ralph Morini
Piedmont Master Gardener
Composting is a great way to recycle organic material like food and yard waste. It uses natural decomposition to create a valuable soil additive while keeping the waste out of landfills, where its decomposition creates methane. Currently, about 20 percent of landfilled waste in Virginia is compostable, so increasing composting makes sense economically and environmentally.
Composting turns organic waste into a rich, dark, soil-like substance called humus. The decomposition is done by organisms such as bacteria, protozoa, fungi, beetles and earthworms, depending on the process used. While organic matter will decompose over time under most circumstances, you can speed the process.
How to Make Compost
Create compost batches out of a mix of high-carbon (brown) and high-nitrogen (green) inputs. Typical browns include yard wastes like leaves, hay and straw, wood chips and sawdust. They can also include household wastes like food-soiled napkins, paper towels, shredded non-glossy paper and cardboard and hair. Greens can include grass clippings, green garden waste, fruit and vegetable scraps, coffee grounds, tea bags and eggshells.
Home composters should not include meat, grease, bones, dairy products, oils and egg yolks. They take longer to decompose and can attract varmints. Never use pressure-treated wood sawdust or shavings, coal or charcoal dust, black walnut leaves or twigs, or herbicide-treated or diseased plant waste.
To achieve “hot composting,” which can reach temperatures of 130 degrees or more, create batches where the ratio is about two times the amount of browns to greens by volume. Hot composting provides the fastest decomposition while helping to kill weed seeds and pathogens.
Cut materials into small pieces to increase the speed of decomposition. This increases the surface area for microbes to attack. Chop up kitchen waste and mulch grass and leaves to help the process.
The batch should be aerated by turning it regularly, typically weekly. As materials break down the batch will settle, forcing air out of the pile. Decomposition will change from aerobic (oxygen-fed) to anaerobic (without oxygen), which is smelly and produces methane, a greenhouse gas.
Compost batches should be moist but not drippy. While aerating, check moisture. Add water if it looks dry. If it is dripping wet, increase aeration frequency and cover it if rain is expected.
A good-size compost batch is a three- or four-foot cube. This is small enough to manage but large enough to provide the insulation necessary for the core to reach the desired high temperatures. Smaller batches will still decompose and yield a good product, but will take longer to break down and are more likely to sprout weeds. Time from initiation to completion of a compost batch can be from three or four months to a year or more depending on input mix and management. It is ready when the material is loose, dark, rich smelling and the inputs are no longer recognizable.
If you add to the pile during the process, screen the material to separate older, finished compost from less decomposed, newer inputs that require longer processing.
Further information is available in the Virginia Cooperative Extension publication “Backyard Composting.”
Why and How to Apply Compost
Compost benefits soils by adding organic matter and the soil organisms that make soil nutrients available to plants. It loosens fine soils like our local clay, allowing easier water entry, while providing absorbency that helps hold moisture longer in our sandy coastal soils.
In new beds, spread a couple of inches on the surface and till it in to loosen and enrich the existing soils. For established beds, spread it on top or work it into the soil surface, letting soil organisms carry it deeper over time. To enrich potting soil, add about one-third compost to your favorite mix.
Alternatives to Open Composting
If your situation isn’t suitable for an outdoor open composting setup, there are other options. Closed bins for outdoor composting are sold at big box stores and online. Look for a capacity that reflects the quantities of material you have available, easy entry and extraction and a convenient aeration method—by barrel rotation, for example. Then follow the guidelines above for materials, aeration and moisture. Closed containers are neat and eliminate odor and varmint risks, so are good in restrictive situations.
Vermicomposting uses special earthworms to eat and excrete fruit and vegetable wastes mixed with shredded paper and/or leaves to create nutrient- and microorganism-rich “castings,” a great soil amendment. It can be done cleanly and is a good solution for apartment dwellers. The worms require temperatures in the 65- to 70-degree range. The EPA publication “How to Create and Maintain an Indoor Worm Composting Bin” provides how-to details.
If you want to compost food waste but can’t compost it yourself, consider dropping it off at the McIntire Recycling Center in Charlottesville or the Ivy Material Utilization Center. For Charlottesville residents, there is a drop-off at City Market and a few locked locations that residents can access via pass codes in and around the city.
There are also a couple of local composting companies that will perform residential pickup for a monthly fee and, in return, provide complimentary finished compost on a periodic basis. Learn more at their websites, www.lifecycleorganics.com/residential and www.blackbearcomposting.com/residential-collection.php.
Composting is a pure good thing. There are many ways to approach it, at least one of which can work for almost everyone. Why not give one of them a try?