There are several ways in which compost heaps can be made and various theories exist as to the way in which they should be treated. There are two important points which are essential for successful compost making and these are adequate drainage and aeration and sufficient moisture.
A compost heap is a necessary feature in the average garden. It provides a means of collecting the surprising amount of waste material which is gathered together during regular garden maintenance and it supplies the garden, or rather, the soil, with valuable organic matter. This organic matter fulfils several vital functions. It helps to improve the structure of the soil, especially the heavy clay types and the light sandy kinds. It encourages a vigorous root system and also acts as a sponge to retain moisture. Light, sandy soils tend to dry out rather badly and a high humus content is necessary to overcome this problem. Well-rotted composted vegetable waste can be used as a mulch around plants and between rows of vegetables where it will smother small annual weeds and prevent the surface soil from drying out badly.
It is advisable to give some thought to the siting and layout of a compost heap, particularly where the garden is small. A compost heap can look ugly and untidy if neglected, but fortunately there are several ways in which the material can be contained neatly and efficiently. Although the heap should be placed in an unobtrusive position in the garden, it should not be put in a position which is damp, heavily shaded or closed in. In these conditions the waste material can become offensive and will certainly not rot down into the dark friable mass it should.
The size of the area a compost heap will require will depend naturally on the size of the garden and especially on the number and sizes of the lawns, for the biggest proportion of compost heap ingredients consists of lawn clippings. The usual recommendation is that the heap should not be more than 90cm (3ft) wide or 90cm (3ft) in height when first built. There will be considerable shrinkage later on due to the decomposition of the waste vegetation in the heap. One of the neatest ways of making a compost heap is to purchase a specially constructed bin or container. Some are made from extra stout gauge wire, stove enamelled dark green, others have a rustic appearance with a strong wooden framework. Most types have either a removable side or one which hinges so that the heap can be filled or emptied easily.
It is quite an easy matter to construct a compost bin from the following material: four corner posts 1.2m (4ft) long (30cm (l ft) to be inserted in the ground), and 5-7cm (2-5in) square. The sides or `filling' in pieces are made from 90cm (3ft) lengths of timber 7cm (3in) wide and at least 2.5cm (1in) thick. Six will be required for each side making a total of 24 pieces. They are spaced approximately 10cm (4in) apart and screwed into the corner posts. To provide for a removable side, one set of side pieces, 3cm (1 1/4in) less in length than the others, are screwed to two separate corner rails 5-7cm (2-5in) wide and 2.5cm (1 in) thick. The complete unit slides into two of the fixed corner posts, in a groove or channel made from two 90cm. (3ft) pieces of 2.5 x 7cm (3 x 1in) timber spaced from the two fixed corner posts by two thin strips of wood 3cm (1 1/4in) thick and 2.5cm (1in) wide. All timber must be thoroughly treated against rot. The ends of the corner posts should be well soaked for several hours before they are inserted in the soil.
Where appearance is not important, or where the compost heap is so sited that it can be hidden from view, old sheets of corrugated iron could well be used in the construction.
The successful decomposition of waste material in a heap depends on the action of bacteria and fungi. The bacteria depend on plenty of nitrogen as food and the rate of decay can be increased by supplying some readily available nitrogen. This can be provided by sprinkling the material with a nitrogenous fertilizer such as sulphate of ammonia or Nitro-chalk. Another method of adding Nitrogen is by placing layers of good quality, fresh animal manure between the layers of garden waste. The heap is, in fact, built up in sandwich fashion with alternate layers of manure and waste.
To get rid of air pockets, each 15-20cm (6-8in) layer of material to be rotted down is trodden fairly firmly. It is customary, though not absolutely essential, to cover each trodden layer with a further layer of soil, about an inch thick. The next layer of waste material is put on this and trodden when it is about 15-20cm (6-8in) There are proprietary preparations on the market which accelerate the decomposition process. Some are specially formulated to deal with tougher ingredients of a heap such as herbaceous trimmings, pea and bean husk, or top growths. Others are particularly suited to the softer materials such as lawn clippings, lettuce leaves, annual weeds and such. Some proprietary formulae include seaweed which produces a very rapid fermentation of the heap. These accelerators are sprinkled on the layers of waste as the heap is built up, in lieu of the nitrogenous fertilizers mentioned.
Where the tougher materials are to be rotted down without the use of a proprietary compost maker, it is a good idea to bruise or chop the stems to aid rotting. Plenty of water must be provided also as this type of harder waste is built into a heap. Some gardeners can obtain quantities of straw and this is very useful as an addition to the compost heap. As a successful heap requires plenty of aeration and drainage, it is wise to start a heap with some of this coarser material at the bottom. Some gardeners like to drive in one or two stakes into a heap so that, when they are withdrawn, air holes or passages are provided which pass right into the material.
Although a well-made compost heap should rot down satisfactory by itself, the contents can be turned after a period of three to four weeks. This is done by transferring the heap to a position close by its original one. Forkfuls of rotting waste placed in the same area, but as the work is carried out, the outer portions of the heap are placed towards the center of the new one. It may be necessary to add a little water to areas which may be a little dry.
It is necessary to appreciate the fact that acids are produced as byproducts of even the most favorable decay and that too much acid will spoil compost. This problem can be overcome if some lime is included in the heap. This can be done if some powdered chalk or limestone is sprinkled on alternate layers of waste vegetation. A fertilizer or a dressing containing lime such as Nitrochalk can be used instead. It is important to note that lime and chalk must not be allowed to come into contact with sulphate of ammonia which might be used as an accelerator. If this is done, ammonia will be liberated and nitrogen lost as ammonia gas.
Decay is also hastened in a fairly warm temperature and in a damp atmosphere. The spring and autumn periods, therefore, will be times when rotting down will be at its peak. One would assume that the summer months would be ideal also. This is true to a certain extent, but if a heap is situated where it receives the direct rays of the sun, considerable drying out of the material will result and decay will not be as rapid.
Much of the value of the compost can be lost if the heap is exposed for long to rain. The nutrients will be lost by being washed away. Where compost has to be stored for any length of time, it is wise to provide some form of shelter for it. An open-sided shed is suitable or a temporary roof can be made. To do this, four strong posts are required about 5cm (2in) square. Two of these should be about 15-25cm (6-l0in) longer than the others. Their total length should be such that they clear the top of the compost heap by 60cm (2ft).
The longest posts are inserted at the front of the compost heap, close by the existing posts or bin sides. The other two posts are placed at the use of the heap. Across each pair of posts a rail should be fastened on which the roofing material will rest. The two rails should be cut from timber approximately 5 X 3 cm (2 x1.5in) in section.
Various types of material can be used for the roof. Corrugated metal sheets or cheap PVC sheets are ideal. The sheets are nailed or screwed down on to the cross rails. Where necessary, an overlap of 5-7cm (2-5in) on the sheets should be provided. The finished roof will have sufficient pitch or slope to shed rainfall. The sheets must be purchased large enough so that they overhang all four sides of the compost heap by at least l0cm (4in).
There are different opinions as to the length of time compost should be kept before it is ready for use. It must be kept until it has decayed to such an extent that the individual ingredients of which it is composed can no longer be distinguished. Usually the material is in an ideal condition when it has become a dark, friable or crumbly mass. A slimy state is not satisfactory and shows that the heap has been made up incorrectly.
In warm weather, soft refuse will take about four to six weeks to decay but in winter the period will be much longer, and anything up to three or four months will be necessary before thorough decomposition has taken place Where the refuse is harder or tougher, the period necessary for decomposition will be longer.
But the best of soils in both content and texture is useless unless it is moist. Plants need water to sustain themselves and because all plant foods are absorbed in the form of liquid chemical compounds. The source of nearly all the water that a garden needs is natural rain, and only in comparatively rare periods of drought is artificial watering necessary. This is a relatively simple matter today with the many watering aids available to us, some of them automatic. The main rule when watering is to do it thoroughly, for if only the soil surface is moist the roots of plants will tend to turn upwards in the soil towards this area and expose themselves to drought or to burning by the sun. It is almost impossible, except in low-lying areas or poorly drained soils, to over water artificially. Over watering occurs with repeated heavy rains.