This Entry was updated 30/11/09.

The days have long since passed when it was considered eccentric to understand the intricacies of a garden compost heap. Now we are all armed with an understanding of recycling and the harm that the waste that ends up in landfill sites has caused our countryside; composting has come of age. Although many local councils will take away materials to be composted centrally, and will collect these materials from your kerbside, there is still a need to understand how a home composter can be beneficial. Often, compost heaps are poorly understood, and may be ineffective. This entry is intended to simplify the process.

What is Compost?

Garden compost is material that has been broken down by decomposition into something that can be spread onto the soil, or dug into it, that will be of benefit to the structure of the soil, or the plants that are growing into it. It can be produced from garden weeds, clippings, vegetable kitchen waste and various other organic* materials. Materials are placed either into a heap, or compost container where they rot down, eventually becoming brown and crumbly. It should be noted that the term 'decomposing' here refers to the presence of helpful organisms or microbes, which do not cause smelly, putrefying processes, but rather similar to general decay, for instance leaving an apple too long in the fruit bowl where it will become dry, brown and shrivelled, rather than say leaving a lettuce in a plastic bag at the bottom of the salad drawer where it will become smelly and gooey.

How is Compost Made?

Layers of waste materials are assembled over a few weeks and left to break down. During this time, which may be weeks or months depending on the time of year, the effect of the decomposition process will cause the heap (or pile) to heat up. This will mean that weed seeds¹ and some pests may be destroyed in the process. The layers should be of various different types of vegetation, grass clippings alone will not make good compost. There should be a distinct layer of one type of materiel, such as general garden weeds, and then subsequent layers of different things such as vegetable peelings, crumbled eggshells, horse manure, small amounts of newspaper or brown cardboard*, sawdust and waste from pet animals such as rabbits and hamsters.

A good tip, to prevent a long walk to your compost heap each time you have a few kitchen vegetable scraps to add, is to keep a small covered container somewhere handy. This will reduce the number of trips down the garden path in the dark and rain.

If there are a lot of fallen leaves, these may be placed into a pile of their own, and left for 12 months where they will produce a marvellous substance called leaf mould. Best to pop into a black bin liner and poke a few holes in. Less messy!

Hedge clippings may be used, as long as they are fairly small sized, but if they contain a lot of woody material, the results may need to be kept for a longer while to allow for complete breaking down. If you have access to a shredder, this will help the materials to break down more quickly, and small amounts of the clippings can be added to the heap in layers interspersed with other stuff².

It may help your compost heap if you can add some form of nitrogenous fertiliser or a product known as compost accelerator, which has a concentration of nutrients and micro-organisms to speed up the natural process of decay.

Your compost heap will become colonised by many different living organisms, both microbial and larger animals. The bugs and creatures that you may find living there, such as woodlice, slugs will be beneficial, munching away on the decaying greenstuff, and themselves becoming part of a food chain for the local bird population, and if you are extremely lucky, slow worms and hedgehogs.

A Bin or a Heap?

There are many purpose-built compost bins for sale, and these are often available from local authorities at subsidised prices. Bins come in all sorts of designs and materials, often being tub-shaped, with a top close fitting lid and a removable side near the base. Other forms are wooden, either made of interlocking slats, or solid sided. Whatever form the composter takes, it should have a top covering, to prevent the heap from becoming too sodden with rainwater, or conversely, becoming completely dried out.

If space allows, and your purse means that you don't have a lot of money to spend on the materials for a purpose-made compost bin, then it is possible to construct a simple heap directly onto the soil surface. Build layers, commencing with a fair amount of free-draining woody-stemmed material. To be effective, the heap will have to have dimensions of at least one metre in diameter and will require a covering of something fairly sturdy, to protect it from the worst of the elements. Old carpet offcuts, placed upside down, can be used. Due to the nature of this type of compost heap, it will be beneficial to turn the contents over once or twice, so as to allow the parts at the edges a chance to decompose. The central portions will be found to have decayed more quickly.

The ultimate in garden compost-making comes when you have the space for a double-bayed, purpose-built wooden bin. This allows the gardener to fill up one side of the contraption, and when the first side is full, begin to fill up the second bay. When the compost has rotted down sufficiently, the gardener may begin to shovel it onto nearby flower and vegetable beds, and any matter that hasn't decayed sufficiently can be easily incorporated into the heap that is still being constructed.

If you have the muscle power to turn the contents of any heap it will allow fresh air to circulate and this will speed the process of aerobic decay. Having more than one container will make this task easier.

Benefits of Making your own Compost

Methane is one of the greenhouse gases that is produced from landfill sites; if you compost your own garden and vegetable waste you will not be adding to the amount of greenhouse gas your household produces.

There should be less need for garden peat to be used as a soil conditioner. Peat is still being removed from peat bogs throughout the world, and this destroys a natural habitat that has taken many hundreds of thousands of years to form. Peat bogs are also being found to be beneficial as a carbon sink. So as well as being environmentally friendly, making your own compost should be a money saving enterprise.

Soil conditioners are used to improve the condition of the soil - in sandy soils they add humus back to the ground. This keeps in moisture around the plant roots and is useful when conditions become dry during periods of low rainfall. In clay soils, additional humus helps to keep the soil structure 'open' thus allowing plant roots to penetrate more easily. The common earthworm depends on a diet of humus in the soil, and the earthworm is one of the most beneficial of garden creatures, munching through tonnes of soil and converting it into a rich friable wormcast, with the nutrients becoming available for absorption by the plant roots.

Good quality home-made garden compost can be spread directly onto the top of the soil in the early autumn. This will provide a simple mulch which can protect some plants from the winter cold. It can also prevent weed seedlings from germinating, by obscuring daylight from them. During the summer, the mulching* effects can help prevent the soil from losing too much moisture, thus cutting down on watering requirements.

Problem Solving

It can be very disappointing to go to a lot of trouble buying a compost bin, filling it up over various months only to discover that at the end of the expected time period, that the 'compost' hasn't appeared as anticipated. Often people will give up at this point and continue to believe that composting is not worth the trouble.

A common finding is that the compost has not broken down and this may be because:

• The heap is too small, and has not had a chance to heat up. If you are limited by the size of the compost bin you have bought, try tipping it out onto a plastic sheet, and use different materials rebuild it in new layers. Then give it another 6 months!

• You haven't added enough stuff in the first place. Keep adding new layers at the top, as the previous layers collapse. If your compost heap is too small, it will never heat up enough to decompose quickly. The optimum size is no less than one cubic metre. Don't forget that as the material disintegrates, it will take up less space, so check your bin frequently and add more to the contents frequently.

• You need to add something to speed the rate of decay, such as a sprinkling of soil between layers of green matter. Those wriggly red earthworms Eisenia foetida may enjoy being added too - as long as they have access to somewhere damp and cool at the bottom of the heap. You may find these under piles of damp leaves, under flower pots or other decaying matter. You may also have a friend or neighbour who keeps a wormery who might be persuaded to give you a few.

The end product is Dry, Dusty and Brown often with a lot of large pieces of woody material remaining. In this case the heap has had too much of one type of material, such as hedge clippings and not enough softer wetter stuff such as potato peel. Remember to vary the layers as you add them. If you have a surplus of one type of material, keep it to one side until you have accumulated some of the other types. Allotment holders will often grow a particular type of plant that they can cut as required and add to their heaps in layers, such as the herb comfrey.

Portions of the heap are Soggy and Putrefying. This can be a case of misunderstanding what is going on inside a compost heap and is caused by too much wet matter and too little air. If you have made a sandwich of wet grass clippings between thick layers of newspaper for instance, the grass will rot, becoming slimy and disgusting. And smelly. Make sure that air can reach all parts of the heap, as the organisms that are breaking it down require oxygen to do so. If this has happened, use your garden fork to break up the contents and add some drier stuff to your heap. If you add newspaper, use it in moderation and scrunch it up.

Items such as orange skins and eggshells are still entirely whole, whilst other stuff has broken down. In the case of orange peel, it is often the fact that the skin has been treated with fungicide and wax, which will prevent the fruit from decaying in the shops. Just throw it back into the base of the next heap - or send orange peel to the local authority's anaerobic digester*. Eggshells are very useful in garden compost, as they provide lime (calcium carbonate) but they break down very slowly when used whole. Crumble them up before adding.

Invasive weeds are still alive and growing happily. This happens if you add a great heap of similar material in one layer, when it has a lot of damp soil clinging to its roots. Clumps of couch grass, dandelion roots, creeping buttercup etc will carry on growing in adverse conditions unless you ensure that you:

• Prevent any light from reaching these plants by completely covering the heap at the top and the sides. Offcuts of weed-repressing fabric can come in handy here.

• Leave these types of weeds root side upwards on a path or similar to dry off, and then add to the heap in stages, when they are assumed to be dead.

• Place these thugs of the weed kingdom near the centre of the heap, where they will likely get the benefit of the highest heat treatment.

Don't forget that composting works faster when the temperatures are higher - so allow a few months in the summer. If you start a heap in the Spring, you may well be using the compost in the Autumn. If you then start a new heap in the Autumn, it may not be ready until at least the following midsummer, but will provide a useful habitat for many garden friends over the winter months.

Keep your compost warm! Place the container, if you are using one, in a sheltered corner. If it is a heap or open bin, make sure it has adequate protection from the elements at both the top and the sides.

Don't expect every scrap of compost to be smooth and crumbly. Often there will be larger woody stems and so on that will need to be returned to start off your next compost heap. These will provide a good source of beneficial organisms and speed up your next attempt. If you need very smooth compost in order to spread in a visible part of your flower borders, invest in a large garden sieve, to produce the required consistency.

To Add or Not to Add

Yes:

Weeds, garden waste, surplus fruits, vegetables, dead flowers, kitchen vegetable waste (uncooked), eggshells, small amounts of hair (for instance if you cut your own family's hair), vegetarian pet waste (sawdust and cage contents), horse manure, the contents of your vacuum cleaner (occasionally!), small amounts of newspaper (for instance if you wrap your vegetable peelings in one or two sheets), small amounts of brown cardboard*.

No:

Plastic or other man-made materials, glass, metal, dog or cat waste*, cooked foods (as there is a likelihood that rats or other vermin will infest your heap), meat or bones (these will definitely smell and attract unwanted creatures). You should also avoid adding certain diseased materials, unless you are sure your heap will heat up sufficiently to destroy the plant viruses and bacteria; diseased prunings from fruit trees* are an example of this. Do not add a vast amount of seed heads from weed plants, unless you can be sure to bring the heap up to a high temperature. They may survive the composting treatment and germinate in your newly dug vegetable rows and make your life harder.

Possibly not

A lot of traditional advice suggests adding human urine to compost heaps. Urine may be of some benefit to compost making as the urea it contains will break down and help increase the level of available nitrogen in the finished product. Having a higher level of available nitrogen will also increase the speed by which the compost forms. However, unless your heap is located in a private, unobserved location, away from other 'conveniences', it is a lot of bother to go to for not a great deal of improvement. And carrying such substances down your garden path is really not worth the effort. Then again, in an emergency, or in moderation, urine will not actively harm the heap. Too much, or too often, and it will smell.

Finally

Compost is good for your soil, your plants, your garden and the environment. However, it is not actually a garden fertiliser, although it has been made from plant materials. For plants to grow healthily they require particular levels of substances such as nitrogen. Garden compost, due to the way in which it has been produced, does not contain significantly high levels of nitrogen. You will still need to fertilise your garden, preferably with environmentally friendly products, such as pelleted, dried free-range chicken manure.

But why 'Zen' you may still be asking... well the answer lies in the fact that you will be connecting with the cycle of life in your own backyard. The springing of life from the soil, and the eventual death and decay of all this once living matter. Returning this once more to the ground and standing back and becoming aware of this process repeating again and again - the very basic building blocks of life.