How to Make Garden Compost

Making Your Own Garden Compost

Having come to the conclusion that ordinary garden compost is as good as any source of bulky organic matter, and cheaper, the gardener must learn how to make good garden compost.

Incidentally, the type of compost we are talking about here is the properly rotted waste vegetation from the garden and home; it should not be confused with seed and potting composts. These are special materials, in which seeds are sown and plants grown in containers of one sort or another.

The kind of compost I am concerned with here, garden compost, is the kind you put into the garden. It can consist of any or all of the following materials: lawn mowings, weeds, hedge clippings, spent vegetable plants, dead flowers, leaves of all sorts, soft prunings, sawdust, wood shavings, wood ashes, straw and hay, pet droppings and animal manures. To this list can be added household waste such as cabbage leaves, vegetable peelings, tea leaves, egg shells and even the contents of vacuum cleaners.

how to make garden compost More or less anything of vegetative origin can be used to make garden compost. When discussing garden compost, I am referring to the decayed or decaying remains of these materials. What is called ‘well rotted’ compost is a dark brown, rich material that is fairly dry and which easily breaks up in the hand.

Woody materials, such as thick hedge clippings and prunings, take a long time to decompose but will, eventually, provide the most humus, humus mainly being derived from the lignin in woody material. As long as twigs and the like are chopped up into small pieces with a shredder or something similar, they can be a valuable raw material but are still best mixed with softer tissues. If large prunings and bits of wood are available, they should first be burnt and the ashes added to the compost heap or bin.

Newspaper in small amounts, such as from the bottom of pets’ cages, is splendid, especially if shredded, but large quantities must be avoided. Not only does it take a long time to rot down, it is also of little, if any, value to the soil.

There are very few things of organic origin that cannot be turned into compost but it should be remembered that some materials are only suitable in small amounts. We have already mentioned newspaper but too many evergreen leaves or pine needles also take a long time to break down and become usable. The roots of perennial weeds, such as docks, thistles and ground elder, must be dried and killed before composting them; alternatively, they should be burnt or put in the garden waste recycling bin.

Rhubarb leaves are often said to be bad for a compost heap, but they are perfectly safe in what might be called domestic quantities. It is when large amounts are put in over the course of weeks that trouble might arise. There’s nothing mysterious about them except that they contain an extraordinarily large amount of oxalic acid.

Anything which gives rise to acidic conditions is bad because decomposition occurs best in a neutral or alkaline environment.

Plants infested or infected by pests and diseases are also frowned upon by many gardeners but most are destroyed either by the heat generated in the heap or by the very fad that they are in a hostile environment for a considerable time. Some are best avoided, though. These are the soil-borne ones and the victims of such things as club root disease, cabbage root fly and carrot fly should not be put in a compost heap.

Lawn mowings are perfectly suitable for composting — in fact they often form the backbone of the heap in summer. However, they are much better if mixed with other and coarser things first. In a thick layer, they are apt to lie cold and soggy after the initial heat generation.

Another point to bear in mind about mowings concerns those that come from a lawn that has been treated with a selective weedkiller. If the treatment took place from April to the end of July, the mowings can be added to the compost heap and it will be quite safe to use the compost in the autumn. If, though, the treatment was after July, then it is safer to leave the compost until the spring just in case it still contains traces of the weedkiller. This is worth mentioning because many gardeners beg, borrow or steal raw material for their compost heaps with little knowledge of its history.

On the subject of lawn weedkillers, it used to be quite common practice to grow tomatoes in partially decomposed straw bales. This is still fine in principle but it must only be done if you can be sure that the corn crop from which the straw came was not treated with a hormone-type weedkiller before it was harvested; these contain the same chemicals as lawn weedkillers. Tomatoes are particularly sensitive to these weedkillers and will be damaged by them if applied in your compost.

To return to composting; the greater variety there is in a heap, the better the resulting compost will be. A mixture of firm and soft materials will give good results.

Having looked at the sort of things that can and cannot be put in the compost heap, it would be helpful to know how compost is formed so that the knowledge can be used to your advantage. The decomposition of waste vegetation is carried out by beneficial micro-organisms, which need air (oxygen) and moisture to survive and operate efficiently. The amount of air and moisture required, whilst not being critical, is important, in that too much air will lead to the raw materials drying out whilst too little will encourage the wrong type of microbe.

Too much moisture will force out a lot of the air and thereby reduce the microbe population. At the same time, it will discourage the build-up of heat within the heap. Too little moisture will cause the whole process to grind to a halt.

A good supply of nitrogen is also essential as this forms an important part of the diet of the micro-organisms. Whilst a certain amount is provided by the plants’ remains, the whole composting process is greatly speeded up if extra is added. Nitrogen used for this purpose is referred to as an ‘activator’ or ‘accelerator’ and there is one particular proprietary product, Garotta, which is available in all gardening retailers.

Given a correctly built heap made with the right material, decomposition will occur by itself; the use of an accelerator simply hastens the process and makes it more complete. This speeding up may not seem particularly important but it means that more heat is generated during decomposition and this is vital if weed seeds and other undesirables in the heap are to be destroyed.

The word ‘heap’ keeps cropping up in relation to composting and this is certainly the traditional way of making compost. However, there are heaps and there are heaps, and an untidy heap is an abomination, whether it be large or small.

Anything that looks like a pile of garden rubbish thrown into a corner is likely to produce correspondingly awful compost, as well as creating a general air of slovenliness. Before we start making compost,therefore,there are several questions that have to be answered concerning the type of heap, or other container,that is going to be most convenient for us. Firstly, how much raw material is likely to be available? Secondly, how much compost is going to be needed? And finally, is the compost going to be required all at once or as a steady supply throughout the year?

If there is only a small amount of raw material or the need for compost is strictly limited, then a small heap or, better still, a ready-made composting bin, is usually the answer.

On the other hand, if waste vegetation is plentiful and all the compost that can be produced is used, then one or more large heaps would be more sensible. This would also be the best system where compost is only needed once a year for, say, digging in during the autumn.

If, though, compost is going to be wanted for various jobs throughout the year, it would be wiser to have a number of bins or small heaps with compost maturing on a sort of production line.

Where it has been decided that bins are inappropriate, the question arises as to what is the best way of containing a heap so that it looks tidy and operates effectively. The heap should be as near round or square as is convenient, to encourage the quickest and most even decomposition. The width should be not much more than 4-5ft (1.2-1 .5m) but the length can be up to about 6ft (1.8m). The width is the important measurement because, with a wider heap, air will have difficulty in penetrating to the centre. For the same reason, 3-4ft (0.9-1 .2m) would be about the maximum desirable height.

The ideal site for such a heap would be in the angle of a fence or wall, where two sides are already provided. In this case it is better to put a sheet of tin or something similar against the fence or wall to prevent its deterioration or the bridging of any dampcourse. The other two sides can be made of corrugated iron with holes driven through, or planks nailed I cm apart to upright supports.

Wood is generally considered superior to corrugated iron, not only because it looks better but also because it provides better insulation against the cold in winter.

If you decide to have a bin as opposed to a heap there are several models to choose from, or you can even make your own. Bins which incorporate perforated polythene sheeting or which are made of more substantial plastic, wood or even bricks all have the advantage of retaining heat and moisture quite well in spite of the small volume.

The one proviso is that the bin should have atop, as this will not only keep the heat and moisture in but will also prevent too much rain getting in. Nor is the necessity for a top confined to bins; traditional heaps also operate far better when covered.

The size of compost bins varies but they’re somewhat bigger than a large dustbin. Their shape, material and effectiveness are about as variable as their price.

Unfortunately, the high price of some models has deterred many newcomers to gardening from even setting foot on the composting ladder; they assume that all other aspects of the job are equally as expensive. This is absolutely wrong and the makers of highly priced but poor bins are doing neither themselves nor the gardeners any good at all. I have to include most rotating bins here; they’re far too expensive for what benefits they may have.

If you fancy having a go at making your own bin, very good results can be had from old dustbins with the bottoms knocked out and some holes punched in the side; and the original lid makes an excellent cover.

Another approach is to make a wire netting cylinder 3-4ft (0.9-1 .2m) high and not less than about 30in (75cm) across. This is supported by canes woven through the netting and a bottomless dustbin bag is placed inside to enclose the compost. It looks a bit Heath Robinson, or rough and ready, but works admirably and costs very little. Heaps and bins smaller than this are not a good idea, as insufficient heat is generated and retained.

Having set the scene, the time has come to start composting. Most gardens produce a range of useful materials and, for the best results, these should be mixed together, building the heap up in layers.

If an accelerator is being used, this should be added every 6in (15cm) or so.

Try to mix dry and wet materials together so that the moisture content is reasonably even. If anything is really dry, it should be thoroughly soaked before it is added to the heap.

A careful firming of the heap or bin is needed when fairly woody materials are in use in order to exclude large air pockets. If the heap appears to be drying out in the summer, it is perfectly in order to wet it so that activity is maintained. This should not be overdone, or excessive cooling may take place.

In the past, and before the days of effective accelerators, it was common practice to build up a compost heap in the course of one year, turn it inside-out and upsidedown and leave it for another year. This ensured that it was completely and evenly rotted and in a fit state to use. If an accelerator and a good heap or bin are used, this is not usually needed.

When a heap or bin is complete and has been properly made, cover it and leave it to decompose. This will start very quickly. The time taken for compost to become sufficiently decomposed and usable will vary enormously. The biggest variables are the nature of the raw materials and the time of year.

If soft material is being composted in the summer, it can be fully decomposed in about two months. On the other hand, chopped up prunings put on in the late autumn are unlikely to be fit for at least six months or even a year.

One of the slowest materials to decompose is autumn leaves. In reasonable amounts, these can be mixed in with the other vegetation to be composted but, if there are a lot, it is best to deal with them on their own, and the addition of an activator is a great help. Also, make sure it stays moist.

The formation of good leafmould usually takes at least a year but this will vary with the type of leaves. Beech and oak are two of the quickest to rot down but plane, sycamore and horse chestnut take a lot longer because of their thick veins and stalks.

Some people recommend adding layers of soil to a heap to provide additional micro-organisms. Although the introduction of soil in the natural course of events, such as on plant roots, is quite in order, the deliberate formation of layers of soil can seriously interfere with the composting process by creating cold layers in which no decomposition occurs at all.

Lawn rakings are another valuable source of material for composting. These are perfectly safe, even if they do contain a high proportion of moss. Although this may not rot down completely, there is no risk of any moss establishing itself in other parts of the garden when the compost is finally used.

If it is anticipated that a particular batch of material is going to be reluctant to break down, the addition of an activator immediately above it normally puts matters right. There are, of course, occasions when a lot of the same material turns up all at once; autumn leaves are a good example. Evergreen leaves and pine needles are best added to the normal mixed compost heap because, on their own, they can take years to rot down. No leaves need be rejected; they all make good compost if treated correctly — it’s just that some take longer to decompose than others. All leaves should have plenty of water when being composted.

Sawdust is tricky stuff, but also very valuable if dealt with properly. Its woody nature makes it an excellent raw material for humus. It does, however, take a long time to break down. In small amounts it can safely be added to the general heap but, if a lot is available, it is best composted separately in much the same way as leaves. The other answer is to build the heap with thoroughly wet sawdust and mix in the activator as the heap is being made.

Small amounts of straw can be mixed with grass mowings and added to the heap. The grass will then make better compost and the straw will break down quicker. Large amounts, however, are best composted alone. There are several ways of doing it, all of which benefit from an activator being included:

  1. By watering the straw and layering it with green and sodden material.
  2. By only watering it.
  3. As in 1, but not watering it and allowing the rain to provide the moisture. This takes the longest of all.

When composting straw, make sure that it is thoroughly loose and always stack it high rather than wide — it decomposes much more quickly.

One of the best ways to decompose straw is to build a sort of stockade of bales and fill up the middle with loose straw. This keeps the heap tidy and allows it to decompose right up to the edges. Tread the whole thing down when completed and give it a thorough soaking.

The retaining wall need not be bales – planks or boards are just as good if held in place with stakes. The advantage of using bales, though, is that, when the composting of one batch is finished, those used for the wall will be half rotted themselves and can be shaken out for the next batch of compost, whilst fresh bales are used for the new walls. As a rough guide, two tons of dry straw will need a heap about 9ft (2.7m) square whilst 6-10 tons will need about 18ft (5.4m) square.

If materials other than straw are included in the heap, spread them out evenly. Tread the heap down as before and give it enough water to soak it thoroughly. A heap can perfectly well be built without walls but it is not as efficient and, of course, the straw does not rot right down to the edges.

In some parts of the country, raw materials like bracken and seaweed are in plentiful supply and these make particularly good compost. Bracken contains a lot of potash and is best treated like straw.

When using seaweed for composting, it should first be allowed to drain to get rid of most of the salt. The best system is then to mix it with straw before composting it. Normally no activator is needed because of the readily available nitrogen it contains.

If a lot of annual weeds are going to be put on a compost heap there is always a danger that any seeds they are carrying will simply be distributed when the finished compost is spread. The obvious way of avoiding this is to ‘harvest’ the weeds before they come into flower but, should this not happen, flowering and seeding weeds should be put in the centre of the heap and then covered with other material to stop them growing and releasing mature seed. The greatest heat is also produced in the middle and it should kill the seeds.

Covering all live weeds is particularly important in the winter when they are apt to stay alive, even when uprooted, in the cool and damp conditions that are found on top of the heap.

Something that falls quite neatly into the category of composting is the use of turf to form the basis of the other kind of compost; seed and potting mixtures for growing plants in. If you are making your own John Innes-type of compost, you will need a good supply of fibrous loam. One of the best sources of this is old grassland. Start by stripping the turves off so that there is about 5cm (2in) of soil below the grass.

Lay the turves on the ground, grass side up, and put the next layer on them grass side down to form a sort of grass sandwich. Carry on building like this until all the turves have gone. If you want to hasten the death of the grass and its decomposition, sprinkle some activator into the middle of each ‘sandwich’.



05. March 2011 by admin
Categories: Compost Making, Soil Cultivation | Tags: | Comments Off on How to Make Garden Compost


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