The Compost Heap

Every organic garden should have at least one compost heap, where garden and kitchen waste can be broken down by microbes and other soil dwelling creatures to produce a good soil improver. Making compost is not difficult and is an excellent way to recycle waste. Many gardeners take great pride in their home-produced compost and all gardens can benefit from this sustainable approach to soil improvement.

A position in full sun will give the compost heat additional heat, allowing the contents to decompose more rapidly. If time is not a key factor, partial shade or even full shade will do. Compost is easily made in a freestanding pile in a sunny or partially shaded area in the garden. Alternatively, simple structure can be used to contain the pile. These structures can be made in a variety of materials, including wood, bricks, pallets or even a stack of used tyres. It is most important that there is good drainage. An average compost heap should be around a cubic metre, you can make it larger but smaller will not really work.

When adding waste materials to the heap make sure that they items are as small as possible. The more surface area is exposed the quicker it will decompose. If you have a shredder, shred all materials before adding to the compost heap. Many gardeners add a small amount of good quality topsoil in order to introduce microorganisms that will speed up the process of decomposition.

The potential ingredients of your compost heap will be either 'brown' or 'green'. Browns are dry and dead plant materials, such as straw, hay, dry brown weeds, autumn leaves, nutshells, shredded paper, pine needles, tough plant stems and woodchips or sawdust. Because they tend to be dry, browns often need to be moistened before they are put into a compost system.

Greens are fresh (and often green) plant materials, such as green weeds from the garden, fruit and vegetable scraps, green leaves, grass clippings, teabags, coffee grounds, seaweed, eggshells, fish scraps, green manures and fresh horse manure. Compared with browns, greens contain more nitrogen. Nitrogen is a critical element in amino acids and proteins and can be thought of as a protein source for the billions of multiplying microbes. A good mix of brown and greens is the best nutritional balance for microbes. The mix also improves the aeration and level of water in the pile.

You can make your compost heap in two ways, either by the 'cold pile' method or the 'hot pile method. For the 'cold pile' method you start by making a pile of 'browns' such as autumn leaves, moisten them well and then slowly incorporate 'greens', such as kitchen waste or lawn clippings over the next year (with this method it can take a whole year to finish the compost). If it gets very cold in winter cover the compost heap with cardboard or old carpet. In this type of composting there are never enough high-nitrogen greens to get the pile really hot. Turn the pile a minimum of once a month if you have not recently added any 'greens'. This breaks up the decaying mass. If you are using this method make sure that you use roughly equal amounts of 'greens' and 'browns', as too many greens will just create a slimy, smelly mess. Compost heaps with lots of 'greens' added can reach very high temperatures, as much as 70 degrees C, thereby killing weed seeds.

If you are making your compost heap using the 'hot pile' method you should wet the ground under the pile and add twigs or other unshredded browns to provide some aeration at the base. Layer the rest of your materials, alternating green and brown layers of about 15cm (6in) thickness, and add water as you go. Topsoil can also be added as a 2cm (.75in) layer between each cycle of green and brown materials. Finish the pile with a layer of 'browns'. Cover the pile with a lid or piece of carpet to keep out rain and conserve heat. Check to see that your pile becomes hot within a few days. Turn the pile to decrease composting time, this allows all the material to be exposed to the hot centre, thereby increasing aeration. This should be done once a week in the warmer season and once a month in cooler periods. The pile's heat should peak every time you turn it, although the peak temperature will be lower with each turn. Always make sure that the pile remains moist, but avoid over-wetting.