- Backyard Composting Guide
- Backyard Composting Flier
- City of Davis Composting Video: Days of Our Piles: Composting 101 (15 minutes)
- 2014 Composting Class Presentation
Composting will happen naturally in your compost pile as microorganisms, bacteria and fungi break down organic material into humus, or compost as we usually call it. There are four essential factors for maintaining a healthy microbial population in your compost pile:
- Aeration: A compost pile should be turned once a week so that it remains aerobic (oxygenated). If you do not turn your pile regularly it will become anaerobic (lacking oxygen) and will begin to emit foul-smelling odors as well as slow down decomposition. Chop materials into small pieces to enhance airflow and increase surface area.
- Temperature: The higher the temperature of the pile, the more rapid the decomposition rates. A proper “hot” pile can reach 120-180 degrees Fahrenheit. A pile that is smaller than 1 yard in any dimension will have insufficient internal volume to maintain high temperatures.
- Moisture Content: The pile should be kept moist but not soggy. If the pile is too wet, water will fill up the air spaces and the pile will become anaerobic. A 40% moisture content is perfect—like a damp sponge. If your pile is usually uncovered, you should cover it with some type of lid or tarp during heavy rains to prevent over-saturation.
- Carbon-Nitrogen Balance: Wet or “green” materials, such as fresh grass clippings and food wastes, tend to be high in nitrogen, while dry or “brown” materials, such as leaves and dried yard waste, are high in carbon. You should try to maintain a balance of 50% dry carbon-rich materials, 35% nitrogen-rich materials, and 15% soil or finished compost.
Surface Area: It is best to have your materials properly shredded before putting them into a compost pile. Doing so will increase the surface area that the decomposer organisms have to feed upon, which makes the organisms more efficient and able to create compost faster. Always mow or chop up material before it is added to the compost pile. Proper particle size reduction can be explained by an analogy using a block of ice. A block of ice will melt very slowly. Crush that same amount of ice, and it will melt much more quickly. The same principle works for a compost pile. A large piece of organic material will decompose slowly, taking longer to compost. That same item, when chopped up, will decompose much more quickly.
Layering: In order to provide a balanced diet for the microorganisms (fungi and bacteria that will do your composting for you) it is recommended that you layer the material that is going into your pile. You can start by adding a layer of carbon-rich brown material, then a layer of nitrogen-rich green material etc. This will give the microbes a proper balance of carbon and nitrogen and help them to break down the material faster.
Composting food scraps
Incorporating food scraps into your compost pile can give you a compost product that is high in nutrients. However, if not done properly, it can attract a number of pests. Make sure that food scraps never make up more than 10% of the total volume of your pile.
Certain food scraps are great to add in your pile, other are not. Acceptable materials include bread, pasta, rice, fruits, vegetables, coffee grounds, and tea bags. Do not add meats, fish, fats, oils, grease, salad with dressing, bones or dairy products to your compost pile.
Always chop up food scraps before adding them. Remember, material that is shredded or chopped up will compost faster than material that is not. An intact orange will sit for months as the tough peel will take a while for microorganisms to penetrate. An orange sliced in half or quarters will decompose much more quickly.
Do not leave food scraps sitting on top of your pile! When adding food scraps to your pile, dig into the center of the pile, add some food scraps, then cover the trimmings. This will prevent pests (rodents and insects) from infesting your compost pile. It is important to avoid having exposed food waste on the exterior of your pile.
Infestation by either rodents or insects is usually an indication that there is an excess of food scraps in the pile. If you notice signs of pests, stop adding this food scraps immediately. After the infestation has ended, you can begin to add trimmings to the pile, but in reduced amounts. If you find you usually have more kitchen scraps than is healthy for your compost pile, consider other composting options. Remember: Most compost bins are not rodent-proof—rodents can chew through plastic and wood. Instead of trying to find a rodent-proof bin, simply make your compost bin a place where rodents will not like to hang out—turn the pile once a week, keep it moist and hide the food scraps inside the pile.
Compost bins can be constructed from any combination of wood, wire, plastic, or concrete. The piles and bins illustrated below represent just a few of the most basic designs. Choose a design and materials to suit your needs, taste, and pocketbook. If you do not want to build your own bin, a wide variety of commercial compost bins are also available. For more ideas, check out the compost demonstration area at the Community Gardens on Fifth Street and see composting happening in the bins along the northern wall.
- Loose Pile—a loose pile is easier to turn but takes up more space than a bin and is not rodent-proof.
- Chicken wire/hardware cloth loop bin—this is one of the simplest and least expensive kinds of bins. You will need about 10 feet of chicken wire or hardware cloth, and a few stakes. The ends of the chicken wire should be fastened together with wire or zip-ties and the sides should be attached to stakes to give it some stability. Once the pile is filled, the stakes can be removed.
- Wooden pallet bin—you can nail a few wooden pallets together to make a single compost bin. To make composting even easier, you might want to consider having two or three open wooden pallet bins, so that you can easily turn the compost from one bin to another. You can also create a bin system like this by zip-tying nursery flats together.
- Plastic hoop bin—The City of Davis Public Works Department offers these compost bins to Davis residents in single-family homes. To get a composting bin you can call the Public Works Department (757-5686) and sign up for the compost correspondence class. A $10 fee will be charged for a compost bin at the completion of the correspondence class.
Maintaining Your Compost Pile
Turn the pile: For fast results and for a healthy aerobic compost pile, remember to turn the pile once a week.
Maintain moisture: Add water to your pile if it starts to dry out. A pile should always be kept moist. There is a simple test to make sure that your pile has enough water. Grab a handful of the material from your pile and squeeze it tightly in your fist. If your pile has the right amount of moisture, the material will clump together and there will be a few drops of water in your hand. If the material is too dry and will not clump together, you need to add more water. If the material is too soggy and drips water when squeezed, you may want to stop adding water for a while, turn the pile more frequently and maybe add more dry material (dried grass or straw).
It will take 3 to 6 months for your pile to turn into compost. During this time, you can continue to add more material to the pile, just be aware that the material added later will not be ready at the same time as the first material you added.
Harvesting Your Compost
You can tell that the material in your pile has turned to compost when you can no longer recognize it. The material will undergo a transformation, and instead of looking like the materials you incorporated into your compost pile, the materials will take on a soil- or humus-like appearance. When the majority of the pile seems to have composted, you can use a seed-planting tray to screen out the unfinished bits. The larger pieces can be tossed back into the pile for additional composting. When you have collected all the compost you should to spread it out on a tarp and leave it exposed to the air and sunlight. Drying out the material will work to cure the compost. It will also make this material easier to spread.
Common Ways to Use Compost
Soil Amendment: Finished compost can be turned into the soil as a soil amendment. As much as six inches of compost can be added to your soil each year. When used as a soil amendment, compost reacts with soil to slowly release both plant nutrients and essential trace elements. Compost can be turned into the soil in the spring in preparation for planting. It can also be spread on soil at the end of the gardening season and allowed to leach into the soil. If only a small amount of compost is available, it can be incorporated in the seed furrow, or a handful can be added to each transplant hole of annuals, perennials, or vegetables. Large amounts of compost can be used to plant trees, shrubs, and vegetable gardens, or to repair or replace lawn areas.
Mulch: Compost is not a typical mulch, yet it can be applied in the same ways that mulches are used. Compost is a stable product that will not deprive your soil of nitrogen. Spread compost two to six inches thick around plants, trees, shrubs, and exposed slopes. This will deter weeds, prevent crusting, curtail erosion, attract earthworms, and conserve water.
Potting Mix: Finished compost can be combined with equal parts of sand and soil to create an excellent potting mix. The compost should be screened to ensure that only fine particles are used in the mix. A simple screen can be made of ½-inch or other small-gauge fencing material and a wooden frame.
Want to learn more about composting?
City of Davis Online Compost Class: The City of Davis offers an online composting class. All Davis residents in single-family homes that complete the quiz with 70% accuracy or better (at least 20 of the 28 questions answered correctly) will qualify to purchase a GeoBin backyard composting bin from the City for $10.
For More Information
- Several books books are available at the Davis Branch of the Yolo County Library.
- California Department of Resources, Recycling and Recovery (CalRecycle)
- U.S. EPA