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Gardening Tips - Composting

Teresa Coughlin explains the secrets of a successful compost heap.

Recycling of nutrients to maintain soil fertility is an essential element of organic farming. Plant and animal wastes are freely available on most organic holdings and these can be composted to provide a ready supply of nutritious organic matter to be returned to the soil. Composting begins the process of breaking down organic material into what will eventually become humus in the soil. Plant waste and animal manures can be composted together or as is more generally the case, separately.

Animal manures

Sheds are usually cleaned out after winter housing when the weather is starting to warm up. The composting process works much faster in warm weather conditions. Regulations on pollution are becoming increasingly strict these days so it may necessary to provide a concrete base for the dungstead with a tank to catch effluent run off. The dung should be piled into a large heap, watering at intervals if the material is dry. Any compacted lumps of manure should be shaken loose. The heap should be moist but not soggy. A white fungus called fire fang will appear on the heap if it is too dry. Cover the heap immediately with a sheet of black polythene if you don't have indoor storage facilities. Loss of nutrients through leaching will diminish the quality of the compost. The heap will heat up quite quickly and a stake can be left buried through the centre which can be removed to check the temperature at intervals.The heating process is essential to destroy weed seeds and pathogens and to begin the breaking down process. The heap will eventually cool down and should be turned at least once and preferably a few times to encourage further breakdown. The contents will shrink greatly in the composting process and the heap should be left for a further six months to mature. During this period , red compost worms will move in and begin to work their way up through the heap. If the heap is on concrete it will be necessary to introduce worms to begin with. Horse manure mixed with sawdust bedding will take longer to breakdown than straw bedding material.

Garden waste

If you do not add garden waste to the manure heap it should be composted separately. This is a bit trickier tham manure composting and it can take a while to perfect the technique. Almost all vegetable waste which rots down easily can be used. Tough, leathery plants and leaves should be shredded before using. Brassica stalks can be smashed with a lump hammer but this is tedious if the volume of plants is large. Unless you are very confident about compost making don't put in diseased plants or persistent weeds like docks or scutch. Household food waste tends to be smelly and attracts rats and flies so keep this separate for worm composting. The heap should be built in one go so this may mean accumulating material for a while before composting. If you have a large volume of waste you can build a big free standing heap. Most people use a bin or enclosure of some sort and the New Zealand bin tends to be the most popular. This is a slatted bin usually a minimum of a cubic metre in size. Two can be built side by side so that a second heap can be made while the first is rotting down. The bin is easily constructed by putting posts in the ground and attaching timber planks in slatted form to three sides. A small space can be left between the slats if preferred to allow for air circulation. The front slats should be removable to allow for emptying the bin. Old floor boards or good quality pallets are ideal for making the bin. A lid is necessary to keep the rain off and to retain heat and moisture.

Building the heap

Assemble all the available waste. Start with a layer of rough material on the bottom to allow for drainage of the liquid produced during composting and the intake of air. The heap should be built of alternate layers approximately six inches in height. Balance soft, wet material with drier straw type material so that the heap is neither wet and soggy or too dry. If the weather is cold an 'activator' such as seaweed meal or manure, particularly poultry manure, can be spread lightly on alternate layers to speed up the composting process. If the contents of the heap tend to be acid a sprinkling of lime can be added at intervals but not on the layers covered with manure. Don't compress the contents of the heap and when the bin is full it should be covered and left to heat up. The temperature of the heap should build up within a week and reach at least 60°C. The contents will shrink a good deal and the heap will eventually cool down. It can then be turned so that the external material will now be in the centre of the new heap to encourage further breakdown. Do not add any new material to the heap while composting. How often you turn the heap will depend on it's rate of breakdown but once should be enough. Allow the compost to mature and use it eventually when it is brown and crumbly and not recognisible as the original material.

The main reasons why a composting process may not be successful are either excess nitrogenous, wet material which turns into a slimy mess, or too much tough, dry material which is slow to break down. In either case start again adding the required material in greater amounts.

For successful composting certain conditions are essential:

Sufficient bacteria and micro-organisms must be present to break down the material. This is not usually a problem as millions of bacteria exist in a pinch of compost.
Air is vital to the de-compisition process. A few stakes can be driven into the heap when building and removed at the end to supply more air.
There must be enough moisture in the heap to enable the micro-organisms to carry out their work.
Food is required by the organisms breaking down compost. Fresh, green material will provide this in summer built heaps but an activator such as manure, fish or seaweed meal is needed in winter.
To reach the required temperature build as large a heap as possible. The larger the heap the more of it will heat up and the faster it will breakdown.

Worm compost

Worm composting is the ideal way convert household food waste into into rich compost. It is not difficult to do and requires little attention after the initial set up. The process does not involve heating up - it's simply a matter of the worms chewing their way through the waste. A standard plastic dustbin can used to house the worms. The bottom six inches of the bin should be filled with gravelly stones as a drainage sump for the liquid runoff. Drill a few holes at intervals below four inches to allow the liquid to drain. This can be collected for feeding plants. A timber board cut to the size of the bin and drilled with drainage holes is fitted on top of the stones. The lid of the bin should also have air holes to allow the worms to breathe. A one inch layer of peat is put on top of the timber and the worms are then put in. These are not the usual earthworms but but the red striped ones which can be found in a compost heap. Begin by adding a four inch layer of kitchen waste - don't overfill. Exclude seeds from the mixture as these can germinate in the bin. Sprinkle a little calcified seaweed or ground limestone on top so that the contents will not be too acid. The worms will gradually work their way up through the waste and the contents should be moved to aerate every time new material is added. Don't overfill the bin as the contents will eventually become too heavy and exclude air. When sufficiently full the bin can be left for a further four to six weeks to mature, aerating occasionally. A second bin can be started in the meantime. Empty the bin carefully leaving a layer containing the worms at the bottom to start a new bin. Insulate the bin in winter to protect from frost. Keep it away from a direct heat source in summer- you can imagine what it would be like to be in a black plastic bin in full sun in hot weather!

Worm compost is very rich and can be used in diluted form to make excellent potting compost.