What is composting?
Composting is our effort to replicate nature’s recycling system. It is simply gathering together waste organic materials and mixing them so that worms and micro-organisms can do their work.
Compost is produced by the natural decomposition of plant and animal material by soil micro-organisms and worms. It is a humus-rich material similar in nature to forest litter. Being a natural plant food, soil conditioner and mulch, compost provides the home gardener with an excellent material to enrich the garden.
Environmentally, composting makes good sense. It is a simple, cost-effective and a natural way of recycling your waste (kitchen and garden) organic material. A valuable resource is conserved: It is cheaper than taking these materials to the transfer station and air pollution (from burning garden waste) is avoided.
Materials you can compost:
Most organic wastes can be composted. This includes all kitchen vegetable/fruit scraps or peelings, tea leaves, soft garden debris such as leaves, garden and lawn clippings, weeds (if they have not gone to seed), untreated wood ash or sawdust, straw, animal manures, seaweed, etc.
Note: Woody material such as cabbage stalks, should be chopped up to increase their surface area or else decomposition will be very slow.
Do not compost:
- Meat, fish, fats or cooking/salad oils (these may create odour and fly problems);
- Wood, bones, inert materials (such as tins, glass, or plastic), or diseased plant material;
- Plant foliage with residues of chemical sprays, especially hormone type weedkillers;
- That gardener’s nightmare oxalis, and other problem weeds such as live twitch, convolvulus, docks, dandelion;
- Toxic material in general.
How do I start?
You can make your own bin or alternatively a number of commercially made compost bins are available. These include plastic and wooden units and compost tumblers..
Siting of bins:
Locate your compost bin in a sheltered, level area of the garden that has good drainage and access. The site should be within reach of a garden hose, and preferably not in full sun. The compost heap should sit directly on the soil.
- Before positioning the bin, fork over the soil on the site in order to aid drainage and encourage earthworms into the heap.
- Ensure adequate aeration is provided at the bottom of the heap. This may be in the form of ventilation openings or by raising the bin on a few bricks etc.
Start the heap by placing a 100-150 mm layer of coarse open twiggy materials (coarse partly decomposed materials from a previous heap may be used) at the bottom of the bin to ensure good drainage and entry of air.
- Top this with a 150-200 mm layer of moist, well mixed kitchen and garden waste eg; fruit and vegetable matter, lawn and garden clippings, weeds or whatever is available. Use as wide a variety of organic material as possible. Do not compact materials after placing in position other than to lightly compress with a fork. If materials are dry, lightly moisten them.
NB: Compost organisms don’t like an acid environment so a light sprinkling of dolomite or lime every few layers is desirable. Within a day or two the heap will heat up and start to shrink. This is the start of the composting process.
Always keep compost covered to retain heat, and to exclude flies and excessive rain .
- Continue to build the compost heap in these alternating layers as material becomes available. When the bin is full, cover with soil, straw, old sacks or similar material to retain the heat. Finally fit the bin lid or cover to keep excess rain out and leave the heap to mature. Turning the compost heap will speed up the composting process, but is not essential. Be wary however of turning the heap on cold days as excessive heat loss may occur and slow down the process. Normally composting will take 3 to 4 months. However if the compost is not turned allow 9 to 12 months for the heap to mature. Turning once a month will aerate the heap and remix the decomposer organisms through the waste material. It also allows you to moisten the heap again. When your bin is full start another.
Chopping or shredding coarse materials into small pieces (about 150 mm) before composting speeds up the process.
Coarse and fine material should be well mixed together.
Air is essential for odour free composting. If necessary a wooden stick pushed through the heap can be used to create aeration vents.
Dampen your heap regularly in summer so as to maintain a consistency of a squeezed out sponge. It must be moist but not soggy.
Decomposition is faster in the warm, summer months because the rate of decomposition is dependent on temperature.
Compost is mature when it has darkened and shows few signs of its original structure. It should be a crumbly soil-like material of pleasant odour. If used too soon, it may borrow nitrogen from the soil as it breaks down. This will limit the nitrogen available to grown plants.
Turn your compost heap immediately if ammonia or offensive odours such as hydrogen sulphide (“rotten eggs”) are produced. This indicates that aeration is inadequate.
The volume of the compost heap needs to be large enough to insulate itself in order to maintain the heat of microbiological activity. A cubic metre or slightly larger is sufficient size.
When mature, spread the compost over the soil to a depth of 25 mm or more and fork it into the top few centimetres of the vegetable garden and flower beds before or after planting. You may need to sieve your compost through netting prior to use. Any stalky or coarse material removed is then recycled into your next compost heap. Mature screened compost mixed with 2 parts loam (topsoil) and 1 part sharp sand makes an excellent seed raising and potting mix. Compost gives newly planted trees and shrubs a good start. Mix 1 or 2 buckets of compost into the soil prior to planting.