Compost Happens Kristina Van Wert, Master Gardener April 2009

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1 What is composting? Composting is the natural process of decomposition and recycling of organic material into a humus-rich soil amendment known as compost. Why compost? adds nutrients to soil and releases them slowly so plants can better utilize them creates good soil structure by binding together soil particles, thereby providing better drainage, better water holding capacity, better aeration, and warmer soils inoculates your soil with micro and macro-organisms that create a healthy soil ecosystem neutralize toxins and heavy metals in the soil ph regulator (compost is close to neutral if not adding acidic items) used for potting soil and seed starting prevents the waste of precious organic materials and slows the filling of our landfills (approximately 30% of our household trash is yard clippings and kitchen scraps!) What makes composting work? Compost happens no matter what you do (or do not do!) Microorganisms, such as bacteria, do the bulk of the work: Psychrophiles are the first wave of microbes, do their best work at around 55 degrees F. As they work on the material they generate heat, causing a rise of temperature in the compost pile. Eventually it gets too hot for them and they are replaced by Mesophiles are the second wave; they work from around 70 to 90 degrees F. Most of the decomposition of a pile is done by mesophiles. But even they can t stand the heat like Thermophiles, which are the most heat tolerant, starting to work at about 100 degrees F and continuing up to about 160 degrees F. This stage will usually last only three to five days, but long enough to get the pile hot enough to kill most weed seeds. Enzymes, are produced by bacteria and assist in the breakdown of materials Macro-organisms dig, chew, digest and mix the material, breaking it into smaller pieces that are easier for further work by bacteria and fungi. Macro-organisms include such creatures as earthworms, mites, grubs, insects, slugs, snails and nematodes. Fungi and actinomycetes decompose the toughest things, the woody materials that the bacteria cannot work on (cellulose, starches, proteins and lignin) Microorganisms need certain things to do their work: Carbon is the energy food (this is the browns that you add to your compost) Nitrogen is protein used to break down the carbon (this is the greens that you add to your compost) Oxygen for aerobes (oxygen using microbes for faster decomposition), otherwise anaerobes take over (non-oxygen users, slower decomposition rate). 1

2 Moisture but not too much or too little. 45 to 50% moisture content is suggested, so the material feels like a wrung out sponge. Around here, where our wet winters can waterlog a compost pile, covering the pile is recommended. But don t forget to water it during the summer! To compost or not to compost? Things you can compost: leaves kitchen scraps grass clippings (mix in wet grass) straw manure weeds and other garden debris feathers eggshells shredded newspaper (no slick ads) seaweed wood ashes coffee grounds & tea bags pine needles hair sawdust hops hedge trimmings ground stone and shells leather wastes peat moss cotton fabrics Things you should avoid: Meat & dairy scraps plastics colored papers Coal or charcoal ash diseased plants pet wastes Oils and fats sludge Toxic chemicals invasive weeds poison oak/ivy/sumac and anything that has been treated with herbicides or pesticides. Always ask yourself the question Would a worm eat this? Herbicides and pesticides can kill the micro and Macro-organisms that your compost ecosystem requires. Browns verses Greens Browns refers to material that are high in the carbon that microorganisms need for energy. This includes things such as: sawdust dry leaves dry grass straw or hay newspaper cornstalks and cobs woodchips twigs pine needles Greens refers to the materials that are high in the nitrogen that microorganisms need to build proteins. This includes things such as: fresh leaves or plants kitchen scraps coffee grounds & tea bags green grass weeds manure and bedding material flowers seaweed freshly pruned trimmings The magical Carbon:Nitrogen Ratio As mentioned earlier, the microorganisms that do the majority of the decomposition work in your compost pile needs carbon and nitrogen to do their thing. The ratio of these materials in the pile is called the carbon/nitrogen, or C:N, ratio, and determines the rate of decomposition. If you have too 2

3 much of the browns listed above, the microorganisms will use up the available nitrogen before they can finish off all the brown material, and decomposition will stop. On the other hand, if you have too much of the greens, the microorganisms will use up the carbon, and the remaining nitrogen will be released as smelly ammonia gas. The recommend C/N ratio is 25 to 30 parts carbon to 1 part nitrogen, often listed as 30:1, but it does not need to be exact. The idea is to be sure to provide a mixture of materials for the microorganisms to work on. You may wish to err on the side of excess nitrogen to prevent your decomposition from stopping. But remember, compost happens, no matter what! Some examples of C/N ratios of material commonly used in composting: Manure 15:1 Leguminous plants (peas, beans, soybeans) 15:1 Coffee grounds 20:1 Manure with bedding 23:1 Alder leaves 25:1 Grass clippings 20-25:1 Vegetable trimmings 25:1 Oak leaves 50:1 Straw, cornstalks and cobs :1 Pine needles :1 Sawdust :1 (hardwoods have higher ratios than softwoods) Shredded newspaper 175:1 Shredded cardboard 350:1 Wood chips 400:1 Composting techniques There are as many ways to compost as there are people who compost. Here are a few general techniques: Pit composting is useful for small amounts of fresh material. Simply dig a hole about 8 to 12 inches deep, add the material and cover. In six months to a year, it will be a great place to put a plant! Trench composting is similar to pit composting. Dig a trench, preferably somewhere you plan to use as garden space next year, and over time layer the trench with compostable materials. When the trench is close to full, cover it with soil and start another one. Digester composting utilizes a commercial digester that is buried in the ground over a deeper hole. Most of the material will disappear into the soil. You can also make your own digester from a garbage can, simply drill holes in the bottom and lower half of a garbage can, then sink it into the ground about half way. Grass-cycling is the technique of leaving your grass clippings to decompose on the lawn, rather than adding them to your compost pile. There are several mulching mowers on the market that chop the grass into fine pieces that quickly break down in the soil. It is a misconception that leaving grass clippings causes thatch- thatch is caused by poor aeration, high nitrogen content, and excessive acidity of the soil. 3

4 Green manure is the growing of a cover crop for a season and then turning the material into the soil. This is good for adding organic material as well and nutrients. Green manures include rye, buckwheat, clover, fava beans, soybeans, vetch, and oats to name a few. Cover crops need to be turned in four to six weeks before you plan on planting to allow the material to decompose, otherwise all of the nitrogen in the soil will be locked up in the microorganisms as they digest the carbon in the material. Sheet composting is when you spread your raw materials, especially straw, manures, grass or leaves over the surface of the soil, then mix it in with the upper layer of the soil and allow it to break down over time. Around here, it is usually best to do this in the fall so the material have the winter rains to help break them down, plus they will protect the bare soil. Mulching uses raw materials to cover the soil. This works well with leaves, straw, manures and woody materials. You may want to run them through a chipper or run over them with a lawn mower first. Vermiculture is the use of worms to compost your materials. A worm bin, red worms and newspaper are required for a vermiculture setup. There are several books written specifically on this topic (which could be another whole talk topic!!). For more info check out Worms Eat My Garbage, by Mary Appelhoff. (Kalamazoo, MI: Flower Press, 1982.) Pile composting is simply making a pile of materials. Often people will store materials and then build a large compost pile, mixing or layering the materials and moistening it as they build. Piles should not be larger than 4 to 6 feet to allow for air penetration. Bin composting systems are one of the most common methods, and can be one, two or three bin systems. They can be as simple as a ring of chicken wire, or as complex as a wood and wire bin with a fiberglass lid! Pallets, cinderblocks, barrels, garbage cans, commercially made plastic composting bins or tumbler systems, garbage bags and straw bales can all be used. The idea is to build a compost pile in a bin and then turn it into either another bin or the same bin. Multiple bins allow you to have several piles in different stages. Bins are nice for containing your compost piles. Setting up your own composting using the bin or pile system Bin and pile composting can be done in two ways: the cold and slow or the fast and hot. Either way you will get compost, but the time and the results will be different. Cold and slow composting Many people have a compost bin or container that they add materials to as they become available- the kitchen scraps from tonight s meal, the trimmings from the bushes yesterday, the wood ashes from last week. Creating a pile with materials over time will lead to a pile that takes much longer to break down and one that will not get hot enough to kill weed seeds. The easiest way to speed up the process of a cold/slow pile is to turn the pile frequently (adding oxygen which will increase the microorganism activity) and to maintain an optimum moisture level (not too dry, not too wet, moist like a wrung out sponge ). Remember the optimum C/N ratio of 30:1; if you are adding large amounts of green materials, try to find some brown materials to add. 4

5 Hot and fast composting Hot and fast composting relies on three important points: materials should be chopped or shredded for increased surface area for microorganisms to work on, there must be a blending of the greens and browns, and the pile must be turned frequently. The goal is to get the pile close to 160 degrees F to kill weed seeds and to speed up the decomposition process. People who are really into composting will often save up materials to build hot piles. One method is to build a pile mixing approximately 1/3 green materials, 1/3 brown materials, and 1/3 unfinished compost or soil. Mix the materials as you add them, and moisten the pile as you build it to a height and width of about 4 to 6 feet. The pile should then be turned every three days (to aerate it and bring the cooler outer materials to the warmer interior) and check the moisture content. The heat of the pile, which will kill weed seeds, should build within the first week, and will cool down by a week or so later. While it requires more work, the resulting compost will be available sooner and weed free. Other considerations: Location of pile. You want your compost to be close to the source of materials, be it the garden or the kitchen, but not so close that it is under the house eaves or downspouts. It can be located in the sun or shade, but it s recommended to keep it open to the south while protected from the cold north winds. Also be sure it s close to a water source and not directly under trees that might sneak their roots in to rob a little lunch! Drainage. Site the compost on a level location with good drainage to prevent puddling and anaerobic conditions. Foundation. Some people like to line the bottom of compost piles with sticks; some prefer contact with bare ground. The sticks help provide drainage and air, but the soil contact helps encourage the micro and macroorganisms to move into the pile. Try both! How big? For hot, fast compost your pile should measure about a cubic yard, 3 feet wide by 3 feet high. Smaller piles have problems heating up and larger piles can end up dry or anaerobic in the center. Windrows, often used in commercial composting, are long compost piles or any length but no wider or higher than 5 or 6 feet. Insulation? During the colder, wetter months you may consider insulating your compost with a heavy layer of stray, hay or leaves. Around the Mendocino coast you may even want to cover the pile with a tarp to prevent the pile from becoming waterlogged. Looks! Just because it is compost doesn t mean it has to be unattractive, especially if it is visible to the neighborhood! If you don t want to show your compost off, you may want to tuck it away in that little back corner. Troubleshooting compost problems Symptom Possible cause Solution 1. Unpleasant odor from pile not enough oxygen turn the pile to aerate it due to compaction not enough oxygen due to over watering add brown materials to soak up excess water, improve aeration and cover in high rainfall areas 5

6 Symptom Possible cause Solution 1. Unpleasant odor from pile cont. if odor of ammonia, add brown material and aerate, too much green material use less fresh grass. if odor of rotten eggs, remove and discard improper uncovered or inappropriate material, bury food scraps food scraps 2. Pile not heating up lack of nitrogen mix in green material not enough moisture pile needs air compost finished? stick a hose into the pile in several locations and add water turn often, add aeration materials If it s dark and crumbly and smells earthy, it s ready 3. Compost is damp and warm pile is too small gather more materials and only in the center rebuild a larger pile 4. Rodents or pests in adding meat, cheese remember not to add meat, compost bin or other undesirables dairy, oils, fats, or bones improper scrap handling bury all fresh food scraps below the surface of the pile, if needed use an enclosed bin 5. Insect pests in compost not necessarily a problem! Not all insects are pests! Even snails and slugs play a role in composting not mixed properly too dry bury all food materials, turn outer materials into pile, hot piles destroy most insects and larvae moisten pile to deter wasps and bees There are LOTS of books out there on composting. Here s some I used: Brooklyn Botanic Garden. Easy Compost. Handbook # 153. Brooklyn, NY: Brooklyn Botanic Garden, Inc., 1997 Campbell, Stu. Let it Rot!. Pownal, VT: Storey Communications, Inc., Harmonious Technologies. Backyard Composting. Ojai, CA: Harmonious Press, Pittenger, Dennis R. Editor, California Master Gardener Handbook (United States of America, Regent of the University of California Division of Agriculture and Natural Resources, 2000) 6