Composting is a practical alternative to the use of animal manures, which may be difficult for the kitchen gardener to obtain. Garden compost is low in nutrients, but is a rich source of humus . It has most of the advantages of other forms of bulky organic matter, without the possible disadvantages, such as difficulty of transportation or unacceptable odor.
Rotted plant refuse is a valuable source of organic matter for improving and maintaining the fertility of soil, and making garden compost from plant remains and kitchen waste has a place in even the smallest of gardens.
The practice also makes a positive contribution to recycling. When we compost household and garden waste materials we reduce the need for collection and dumping of refuse, and also avoid using wasteful and potentially polluting bonfires to dispose of plant remains. All of these factors are in the interests of our natural environment.
Any heap of plant waste will gradually decay and reduce to yield a useful soil additive, but careful management of a compost heap will pay dividends. The goal is to produce a dark-colored, friable material of even consistency that is agreeable to handle and not too wet. This is best achieved by what is called aerobic composting, which involves ensuring that air can get into the bulk of waste material, accelerating decay.
Place compost bins in a screened area, perhaps conveniently near the kitchen; they can be in shade. Depending on the productive garden size and the space available, plan for at least two bins side by side, each about 3–5ft (1–1.5m) square.
The purpose of having more than one bin is to allow the rotting compost to be turned and moved from one bin to another. This exacting process is well worth the effort for aeration.
Bins need to be established either on an 8in (20cm) layer of thin, woody prunings laid on soil base, or with a floor of strong wire mesh laid over bricks. Both methods allow air to circulate at ground level.
You can make your own bins with walls of strong, treated lumber, builders’ pallets, concrete blocks, or even straw bales. Ideally, construct the front walls with removable boards that slot in, allowing the height of the front to be raised as the bin is filled.
A removable cover is essential to keep the heap from becoming too wet, but fit it so that some air circulation is possible over the surface of the compost. Proprietary composting containers made from strong, rigid plastic are available, and these are suitable for use in the smaller garden.
Any bulky matter of plant origin is suitable for composting. Nitrogen-rich material, in the form of leaves and nitrogen-rich additives such as animal manures, will accelerate decomposition. There must be a good balance of material in a heap in order to ensure the movement of air.
Mixing in a proportion of some woody material helps this by preventing the heap from becoming compacted. It is quite easy to ensure a supply of lush, leafy waste during the warm days of summer, but as the growing season draws to a close, the nature of material available for composting is relatively low in nitrogen.
Temperatures also fall, slowing the composting process. At this time rotting can be encouraged by adding nitrogen in the form of a 2in (5cm) layer of animal manures, including litter from poultry or pets such as rabbits.
Alternatively, add dried blood at a rate of 8oz per sq yd (250g per sq m) or a proprietary compost activator. Grass clippings, fallen leaves, and cleared plant debris from ornamental borders will all decay suitably, as will trimmings made from vegetables on harvesting and waste from fruit and vegetable preparation in the kitchen.
Brassica leaves and stems can be added; the stems are best chopped up. Pea and bean plants, including the pulled roots, will compost. Unused root crops can be added, chopped into fragments, provided they are pest and disease free.
Doubts are often raised about adding rhubarb leaves to compost, but this is quite acceptable. Blight-diseased potato haulms can be composted in a well-made heap that reaches a high temperature. Annual and perennial weeds are usually relatively high in nitrogen and the tops will compost well.
Hedge clippings and thin woody prunings will decompose if reduced to small fragments, and for this purpose it may be worth investing in a small shredding machine. Other less obvious materials can also be composted, as long as they are made from natural substances.
Newspaper and cardboard can be added if they are shredded first; even cotton and woolen items that have been cut up can be composted, although they will inevitably take a much longer time to break down than other waste.
MATERIALS TO AVOID
Although the heat generated in a well-managed compost heap will destroy many plant pests and diseases (see Plant Problems, pp.246–264), exclude any material carrying persistent infections, such as club-root in brassicas, black spot in roses, canker in apples, and white rot in onions. It is best not to add brassica roots, which may be diseased; similarly, potato tubers may perpetuate disease and can also be troublesome in re-sprouting.
Be careful not to carry over weed populations in the form of seeds, roots, bulbs, corms, and fleshy parts that may survive composting. All the underground parts of grasses, curly docks, nettles, and oxalis, for example, should be excluded from compost; it is also best not to put in abundantly seeding annual weeds.
Check that grass mowings and straw added to the heap have not recently been treated with selective (or hormone) weedkillers, for there is a small risk of contaminating the crops grown on ground to which these composted remains are added.
It is also important not to put any plastics in a compost heap, nor any waste food products, such as meat, that might attract rats to it.
MAKING THE HEAP
Build the compost heap up in layers of about 6in (15cm) depth, aiming to mix the type of material added where possible. It is best, if possible, to have a space beside the bins to store heaps of different materials until there is enough to make a proper layer, ensuring a good variety of material through the heap. Add chopped, moist straw to a similar depth over each layer to maintain aeration.
Do not allow compacted layers of a single type of plant waste, such as lawn mowings, to lie in the heap, because they will form a slimy mass and create airless conditions that slow the rotting process. The heap must not be allowed to become waterlogged, which will exclude air and lower the temperature.
Keep it covered at all times to keep off rain and maintain warmth and internal moisture. Conversely, the heap should not be too dry, as this similarly slows decay; in warm summer weather you may need to water it.
Rotting waste generates heat through the activity of microorganisms, and a well-made compost heap can reach around 158˚F (70˚C) within three or four weeks. It is most beneficial to turn the heap from time to time, ideally by forking rotting material out of a full bin into an empty one. Move less rotted material from the sides of the bin to the center of the new load, where it will rot faster.
Do this at least once per full loading and preferably more often. The speed of decay is determined by the nature of the waste, but above all by the management of the heap. A heap that is carefully loaded, regularly turned, and has suitable additives can produce useable compost within six months, although it is wiser to plan for a year.
It is not always possible or convenient to make compost in the ideal manner. There is still value in producing bulky organic manure simply by stacking plant waste to rot in the open or in plastic sacks, mixing types as much as possible as for a standard heap.
This method allows less air to penetrate, and is known as anaerobic composting. Complete rotting takes much longer, at least one year and up to two years. Burying waste in a large trench and digging it up once it has rotted down is also suitable on a small scale.
Tree leaves collected in the fall can form compacted layers if not mixed with other materials before adding to a compost heap. They are best composted in a separate container of similar size to compost bins, but with mesh or netting sides. They rot slowly, taking at least a year to produce leaf mold.
This has an excellent friable texture, and is very suitable for mulching and as an ingredient of potting composts. Oak and beech leaves in particular are a great bonus to a leaf mold mix.
Worm composting is a relatively smallscale process, of particular use where space is limited or for dealing with kitchen waste. Dried samples of this small-scale nutrient-rich compost are especially suitable for adding to potting mixes.
There are various sizes and styles of proprietary wormery; alternatively, a plastic bin, wooden box, or any large, rigid container can be adapted. The bin needs to have a lid and good drainage, and to be kept frost-free in a sheltered place. Suitable worms, known as compost worms or redworms, resemble small earthworms but are darker red.
They can be found in rotting manure or plant waste, or be purchased from a specialty supplier. Managing the bin requires experience: only small quantities of kitchen waste should be added at a time. To harvest the waste, spread it on a plastic sheet and place wet newspaper over part of it: the worms will collect under the paper and can be returned to the bin.
THE ROLE OF COMPOST
Any of these types of compost is beneficial: they all make an excellent mulch for fruit canes, bushes, and trees, and for perennial vegetables and runner beans. Although a surprising amount of compost can be made in many gardens, it is likely that it will need to be supplemental to other means of improving the soil’s organic content because of limited production.