Compost and Composting
Composting is the process of breaking down organic material. It is one of the basic principles of organic and biodynamic gardening, and has been in practice for a surprisingly long time. Pliny the Elder refers to composting in his writings from the early Roman era in the first century AD. But it wasn’t until the 1920s when forward thinking scientists and social philosophers such as Rudolf Steiner began to see the profoundly important role composting could play in a modern society. And only now are municipalities in North America contemplating large, industrial scale composting programs to deal with urban waste. More about that later…
In early systems, manure and wasted plant matter from the field was laid in wide heaps for one year or more, by which point it would have broken down into a useful, fully decomposed form. It could then be added to fields either as a top dressing or tilled under, adding important organic matter to the soil. This process improves the body of the soil and helps to balance moisture retention and drainage. It also replaces fertility and nutrients to the soil after being depleted by a season’s planting and harvesting.
In the true biodynamic sense, laying down a layer of well-rotted compost on the surface of the soil encourages soil-dwelling creatures and microorganisms to come to the surface and drag the rich compost down with them, converting it into forms of nutrients that are more freely available to the roots of plants. By top dressing only, one can avoid tilling the soil, which some people feel is unnecessary and even destructive to soil health.
There are scores of different composter designs, but the principles are the same for all of them. Elevating organic waste materials into a stack or heap, surrounded by a well-ventilated barrier, allows oxygen to enter the pile, which in turn encourages healthy aerobic decomposition. This elevation of the stack also prevents it from holding too much moisture – if the pile were lower and wider, moisture would collect at the center and prevent good flow of oxygen in and out of the pile.
So the most basic design of a good composter is a simple cylinder made out of some porous material like chicken wire or plastic mesh. As fresh material is added to the top of the pile, you need a way to remove finished material from the bottom. Some plastic systems come with a convenient door near the bottom, where finished material can be scooped out. If they are well managed, these plastic composters are adequate for a small family with a small garden. The size of your compost system will need to increase as the size of your garden increases, though – partly because of the increased amount of material to compost, and partly because of the increased demand for finished compost.
Managing the compost heap
In order to sustain good aerobic breakdown of compost, the pile needs 4 components working in relative balance:
Carbon: This is sometimes referred to as “brown matter” and it’s usually dry. Carbon can be supplied to the compost by dried leaves, lawn clippings, newspaper, straw, and so on. These materials provide the energy for the microbial action in the pile, and as the microbes break the carbon matter down, heat is produced.
Nitrogen: High nitrogen ingredients to the pile are often referred to as “green matter.” These are the wet organic components like kitchen scraps, manure, and spent plant matter from the garden. The nitrogen materials allow the microbes to reproduce in great numbers, which aids the breakdown of the whole pile.
Oxygen: Without a steady supply of oxygen, the decomposition turns from aerobic to anaerobic, which produces poorly disintegrated, stinky results. Oxygen is used by microbes to oxidize the carbon in the pile, and is essential for proper decomposition.
Water: The microbes require some moisture – too much water will prevent good aeration of the pile, and will result in stinky anaerobic action. Too little moisture will prevent the breakdown of the pile.
As bacteria do their work in the compost pile, they produce quite a lot of heat. This can result in loss of moisture through evaporation, and loss of oxygen through the heating process. So the pile needs to be tended to regularly for it to work efficiently. Generally, it’s a good idea to alternate layers of green (nitrogen) matter and brown (carbon) matter in the pile. For instance, every time you add a bucket of kitchen scraps, you should top it off with a handful of straw, some crumpled newspaper, or some other brown matter.
As the top of the pile grows heavier, the bottom layers will squish together, which reduces the flow of oxygen, and encourages moisture to collect. Turning the compost (taking material from the bottom and putting it on top) is one way to encourage consistent breakdown. Tools like the Wingdigger can be used to pull material from the bottom of the pile up towards the surface. As you do so, you puncture the pile, which encourages good aeration.
The final result, of course, is well-rotted compost soil, or humus. This is dark brown due to the high carbon content, and quite light in texture. In well-processed compost, there should be no large pieces of intact material. Humus is as broken down as it will ever get. When humus is added to garden soil, it actually feeds the organisms in the soil, including earthworms, which in turn, benefit the soil structure and the nutrients available to grow strong, healthy, productive plants.
The City of Vancouver is finally moving to implement home compost collection. City Hall estimates that around 35% of home residential garbage is compostable. The 110,000 homes that now get regular yard trimmings pickups will shortly be able to separate out raw fruit and vegetable scraps, coffee grinds, teabags, and other materials. In January, 2011, the City will expand the project to accept a much wider range of materials such as meat bones, pizza boxes, and the like. The City is also working with the private waste collection companies that collect from condos and apartment buildings, to implement a “third phase” in its compost management scheme.
The City of Vancouver (and many other local municipalities) also now offers composters that are constructed out of recycled plastic. These are available at cost from City Hall, and are adequate for the typical urban family to both reduce their garbage output, and produce good garden humus to enrich the soil. Hopefully this dedication to reducing the amount of garbage headed for landfills will spread as base their own models on the successes of others.