Composting is easy - and with a little know-how, keeping your compost pile efficient, odorless and pest-free is a cinch. Healthy compost piles are moist, warm and free of foul odors, so recognizing an unhealthy pile is not especially challenging - and proper maintenance will quickly become second nature.
We've written before about which items you can compost, and this post will explain how to maintain and troubleshoot your own pile. These basic principles will help you turn those precious organic ingredients into a healthy, functioning compost pile.
The Carbon/Nitrogen Ratio
The scraps you throw into your compost fall into two basic categories: carbon-rich "browns" and nitrogen-rich "greens." You need more carbon in your mix than you need nitrogen, with an optimum carbon/nitrogen ratio of about 30/1. Generally, meeting this ratio means adding about one part brown for every two parts green, giving the decomposers a balanced diet with enough energy and nutrients to eat through everything you compost.
Carbon-rich "browns" are dry, woody materials. Nitrogen-rich "greens" are colorful and usually a little moist. Here are few examples:
- Dried leaves
- Sawdust and woodchips
- Shredded black and white newspaper
- Egg cartons
- Dead, dried-out plants (disease-free)
- Tree bark
- Peanut shells
- Fruit and vegetable kitchen scraps
- Coffee grounds and tea bags
- Green garden cuttings
- Fresh leaves and flowers
- Grass clippings
Because you need to add carbon to your compost every time you add food scraps and other greens, it may be handy to keep a container of dry, carbon-rich materials near your pile.
The carbon/nitrogen ratio balancing act can be as simple or complicated as you like. The easiest approach is to stick to the basic 2:1 recipe. But if you're striving for optimal compost efficiency, or want to achieve a specific soil quality for your gardening needs, check out The Compost Info Guide to find the exact C/N ratios for a wide variety of compostables.
Turn Your Pile
Periodically turn your compost with a pitchfork or shovel so the new material ends up on the warm interior of your compost pile. You need to give those decomposers in the middle a fresh meal to keep the compost working properly. I prefer using a pitchfork because crumbly, dry compost will fall through the prongs while properly moistened compost will not, which helps to gauge the water content in the pile.
Turning your compost also infuses your pile with oxygen, which is essential for the aerobic bacteria that help decompose the materials within. If you have not added materials to your compost heap in a while, make sure you still turn the compost every so often.
Small Particle Size
For maximum efficiency, shred scraps before adding them to your compost whenever possible - the smaller the pieces, the faster and more effectively your compostables will decompose. When you add yard trimmings, for instance, use clippers to cut stems into shorter lengths. Likewise, you can crush egg shells and chop up veggie scraps, fruit cores and peels. Always rip apart newspapers, cardboard and paper egg cartons before composting to distribute the carbon content more evenly.
Moist, But Not Soaked
While too much water will stifle air circulation in your compost pile, causing it to become anaerobic and smelly, not enough can slow or even halt the decomposition process. The moisture content of your pile should be kept at around 50 percent, enough to produce a few drops of water when you squeeze a handful of material. Rule of thumb: your compost should feel like a damp sponge.
To keep your compost wet, water it! When you add scraps or turn the pile, you can use a hose on any dry areas. You may want to position your compost pile near a garden you water regularly so you can easily add water to your compost pile as necessary.
If you notice your compost pile is wet in the middle, but dry on the edges, it might be time to expand. A healthy compost pile is usually at least 3-5 square feet; this size retains moisture and the heat generated by bacteria during the process of decomposition.
Your compost should warm up as scraps decompose. Large piles can grow as hot as 180°F, while small, home composts can be expected to reach 50-113°F. Because smaller composts do not retain as much of the heat generated by decomposition, the decomposition process will take longer. If you are just getting started, your compost pile may take up to a year to fully develop. Add more material to increase the temperature.
If your compost pile is generally well maintained, but not warming up, try adding more browns. Carbon is an energy source that bacteria will devour, heating up their environment. You can also try covering your compost to retain more heat. Add a layer of dirt, straw or other browns to trap heat. Covering has the added benefit of deterring flies around your pile.
In the winter, your compost may freeze. Don't worry - you can still compost by collecting scraps in a dark bin, preferably stored in direct sunlight. Or you can continue to throw scraps on your pile and let them freeze until spring. Either way, your compost will be back in action come warmer weather.
Smells are a bad sign for your compost. If you avoid adding meat and oily foods to your pile, which can attract pests, your compost should not give off odors. Strong, foul smells usually indicate that the aerobic bacteria in your compost are struggling for one reason or another. Remedy your compost's stench with these quick pointers.
- Turn your compost: You may have a heap full of stinky anaerobic bacteria if you are not turning your compost frequently. Try turning your compost every few days to infuse the pile with oxygen so that odor-free aerobic bacteria thrive and anaerobic bacteria do not.
- Add more browns: If your pile smells like ammonia, you've added too much green. Try adding more browns for each part green to for a balanced carbon/nitrogen ratio.
- Top with dirt: You can prevent smells by adding an extra layer of dirt or other brown covering over the top after turning and mixing in more browns.
- Avoid meat or oils: If you don't mind attracting wildlife to your yard, you can feel free to include meats and oils in your compost. It's wise to avoid these items, however, if your compost is close to your home or if you live in an urban or suburban area.
Still have questions? Our series on composting has a lot of helpful information. You can also learn more about the science of composting and how to troubleshoot with the New York City Master Composter Manual or SyracuseCOE's Superior Compost guide. Also, check out City Farmer's Compost Hotline for expert support! Never give up on your compost pile! If something goes wrong, you can usually set things straight in a few days.
A version of this post was originally published in July 2014.