by Pat Allen, Extension Master Gardener (EMG)
Composting is probably one of the easiest tasks around your home/garden. But before you start tossing ‘stuff’ in a pile, you need to know a few facts about composting. Like what is composting, what are its benefits, which materials are appropriate, are there different methods, how do you build a compost, and when will you know when it’s ready.
First, composting is a process of breaking down organic materials into a product that is beneficial to soil and plants.
Composting benefits cover a wide range. Following are a few key advantages: Compost …
- improves soil health & fertility,
- increases the nutrient content of soils,
- promotes higher yields of crops,
- attracts & feeds diverse life in soils,
- makes soil easier to work,
- increases soil porosity & moisture retention,
- suppresses plant diseases & pests,
- reduces the need for fertilizers, fungicides & pesticides,
- encourages healthy root systems,
- helps regenerate poor soils,
- prevents & manages soil erosion problems,
- reduces water demands of plants/trees,
- makes use of home/garden/farm waste,
- decreases waste going into the landfill,
- can reduce money spent on soil amendments, fertilizers, pesticides, etc., and
- can become a revenue stream – removing others’ waste (manure, animal bedding, yard waste, coffee grounds, old produce), selling compost (requires a permit and testing).
Composting basics aren’t terribly complicated, but they do involve a few terms that many people don’t use every day.
Decomposition is generated by mixing a ratio of the following materials:
Ratio of carbon-to-nitrogen – Carbon provides both an energy source and the basic building block making up about 50 percent of the mass of microbial cells. Nitrogen is a crucial component of the proteins, nucleic acids, amino acids, enzymes, and co-enzymes necessary for cell growth and function
- Browns provide carbon and fiber, are slow to rot, and generally come from garden wastes such as dead leaves, and shredded branches/twigs.
- Greens provide nitrogen and moisture, are quick to rot, and generally come from kitchen wastes such as vegetable waste, fruit scraps, coffee grounds and grass clippings.
- Aeration caused by air circulation (oxygen) helps bacteria and other microorganisms breakdown plant material.
- Moisture is essential for microbial activity; material pile must be completely moistened with 50 to 55 percent water.
A mixture between carbon-to-nitrogen ratios, moisture, and aeration generates a well-balanced compost that not only looks and smells like soil but contains rich plant nutrients and essential trace elements.
Additional factors that aid decomposition:
- A pH between 4.2 and 7.2 is best in the beginning; when it rises to between 6.0 and 8.0 compost is finished.
- Temperature between 90- and 140-degrees F helps kill disease organisms and weed seeds and creates an environment necessary for efficient composting.
- Particle size: the smaller the material the faster decomposes.
- The optimal proportion of brown to green materials averages about 30 parts “brown” (carbon-rich) to 1 part “green” (nitrogen-rich).
Typically, ‘wet’, or green materials such as grass clippings, food scraps, and plant cuttings contain a higher proportion of nitrogen than ‘dry’, or brown materials such as wood, paper, and leaves.
The ratio of carbon-to-nitrogen is 2:1 (C: N) layers of browns to greens. But what are browns and greens?
Browns (carbon) are slow to rot materials that provide carbon and dry fiber:
- fallen leaves,
- twigs and branches,
- wood chips,
- paper products: used napkins and paper towels;
- soil or finished compost,
- cardboard, newspaper;
- dried flowers,
- pet or human hair,
- wood or paper pet bedding,
- nonglossy junk mail, or
- dryer lint.
Greens (nitrogen) are slow to rot and provide nitrogen and moisture:
- grass and plat clippings,
- food scraps: break, crackers, fruit, vegetable, cooked starches, jam/jelly
- coffee grounds & tea bags;
- manure (not dog/cat), or
- fish tank water.
Never add the following materials:
- meat or bone scraps,
- fish scraps,
- dairy products,
- fats, oils, or grease,
- dog, cat, humans’ feces;
- kitty litter,
- weed seeds,
- charcoal ash,
- non organic materials,
- citrus rids, corn cobs stalks, husks;
- nut shells (walnut, pecan, and almond);
- coal ash,
- automotive petroleum products,
- yard waste treated with herbicides or pesticides,
- spicy salt, or
- colored paper, plastics, metals, foils, synthetic fibers.
The different methods of composting is all about your time and your energy. Different bin shapes produce different results within a given amount of time. You need to decide which type of composting method suits your needs. Do you want to spend time working in your garden, or do you want the compost to do most of the work? The difference is in whether the compost is hot or cold.
Hot Composting: Active management process, turning materials, maintaining moisture, and maintaining heat.
Slatted Wooden Bin
- Pros: Nice looking, convenient, wide slats for ventilation, modular allows expansion, metal mesh floor deters rodents
- Cons: Can be expensive, eventually deteriorates, requires rodent proofing
- Best Uses: Multi-chambers for community gardens, small ones for backyards
- Pros: Convenient, compact, rodent resistant, holds moisture, good for kitchen waste
- Cons: Can be difficult to turn and access; often expensive, moisture adds to weight
- Best Uses: Rooftops, urban backyards
Bottom-Access Plastic Bins
- Pros: Convenient, compact, moderately priced, sliding base drawer for easy access, contains moisture, good aeration
- Cons: Less attractive than other bins
- Best Uses: Backyards, apartment building courtyards, small school gardens
Cold Composting: Passive management process, gradual organism breakdown, minimal seed breakdown, minimal turning, occasional watering.
Adjustable Mesh or Wire Bin
- Pros: Inexpensive, easy to access, adjustable
- Cons: Not rodent resistant, must be staked in ground
- Best Uses: Holding leaves until your main pile needs browns
Modified Trash Can
- Pros: Compact, secure, inexpensive, easy to create from metal or plastic trash can, holes allow for circulation/drainage,
- Cons: Limited capacity, easily mistaken for garbage can, difficult to harvest compost
- Best Uses: Urban gardens, patios, rooftops
- Pros: Compact size, higher nutrients/activity than microbial compost, higher value product than microbial compost, can also grow worms to sell for fishing or composting
- Cons: May not be able to compost large quantities, not ideal for woody materials
- Best Uses: Use immediately or store, soil amendment for garden or potted plants, kick start transplants, make compost tea
After you’ve decided your preferred method, you need to start building your compost. For the best results, it should be higher than 3 feet but less than 5 feet. Begin with
- 4 inches of tangled branches on bare earth under
- 4-5 inches of brown then 2-3 inches of greens.
- Throw a handful of soil at each layer to introduce more microorganisms,
- top with 4-5 inches of browns, and
- turn every few weeks.
You’ll know when your compost is ready when the following conditions are met.
- Original materials are not recognizable.
- Materials can be screened through 1/2 inch screen.
- Pole temperature is <10 degrees warmer than ambient temperature.
- Color is dark brown or black and smells like earth.
When pile no longer heats, cover it with a fabric weed barrier then let it cure for 6-12 weeks, misting and poking as needed. This additional time:
- results in a more chemically stable product,
- fresh compost can “burn” plants through phytotoxicity, and
- fresh compost can rob soil of nitrogen as the process finishes.
Now that you have the basic information, you may want to know more so you can make several composts. For instance, at my place we have a vermicompost (cold) for our vegetable gardens, a garden compost (cold) for spent plants, a horse manure compost (hot) for aged fertilizer, a chicken manure compost (hot) for kitchen scraps, and a goat manure compost (hot) for our grass pastures.
Yes, composting is a gift because its basic elements are given freely from Mother Nature (sun and rain), select garden and household waste, and soil microorganisms. All you have to do is put them in the correct order, allow them to get hot, add water at the right time, and stir.