By Gregg Kulma, Environmental Engineer
Composting is a good way to recycle your yard and kitchen waste and it reduces the volume
of garbage sent to landfills. Compost is the decomposition
of plant materials into an
earthy, dark, crumbly substance – excellent for adding to houseplants or enriching
Compost does several things to benefit the soil that synthetic fertilizers cannot do. First, it adds organic matter, which improves the way water interacts with soil. In sandy soils, compost acts as a sponge to help retain water in the soil that would otherwise drain down below the reach of plant roots. In this way, it protects plants against drought. In clay soils, compost helps to add porosity (tiny holes and passageways) to the soil, allowing it to drain more quickly so that it doesn’t stay waterlogged or dry out into a brick-like substance. Compost also infuses the soil with vast numbers of beneficial microbes, such as bacteria and fungi. Microbes are able to extract nutrients from minerals in the soil, which they eventually pass on to plants.
Composting organisms require the following elements to work effectively:
- “Browns” (i.e., leaves or wood chips) are added to compost for energy. The microbial oxidation of carbon produces the heat needed for decomposition. Leaves and woodchips tend to be dry, so browns often need to be moistened before they are put into a compost system.
- “Greens” (i.e., green leaves, veggies, etc.) are added to compost to grow and reproduce more organisms to oxidize the carbon. High nitrogen materials tend to be green or colorful and wet, such as fruit and vegetable scraps, green leaves, coffee grounds and tea bags.
- Oxygen is needed to oxidize carbon in the decomposition process.
- Water, in the right amounts, maintains activity without causing anaerobic conditions.
- A good mix of browns and greens is the best nutritional balance for microbes. This mix also helps with aeration and the amount of water in the bin. Browns, for instance, tend to be bulky and promote good aeration. Greens, on the other hand, are typically high in moisture, and balance out the dry nature of the browns.
The most efficient composting occurs with a carbon and nitrogen mix of about 30 to one. Nearly all plant and animal materials have both carbon and nitrogen, but amounts vary widely with wet/dry and brown/green characteristics as noted above. Fresh grass clippings have an average ratio of about 15 to one and dry autumn leaves about 50 to one depending on species. Mixing equal parts by volume approximates the ideal carbon to nitrogen range. Ideal compost temperatures (135 degrees to 160 degrees Fahrenheit) can be achieved with the right mix, but few individual compost units will provide the ideal mix of materials at any point in time – in this respect, home composting is like horseshoes: perfect is great, but close still works.
Posted May 2, 2011