Is it true that a compost bin/heap MUST be built in layers?

No, it isn't true; however let's take a moment to consider why. It is not uncommon for gardening literature to state that a compost heap should be built up in layers, and many keen gardeners will insist that this is the correct way to build a heap. The basis for this advice is mainly to help the gardener attain the correct balance of 'greens' and 'browns', which is important in any compost bin, but especially so if you are trying to achieve a hot heap, which so many gardening books recommend. If you are aiming to put an equal amount of greens and browns in your heap, then the addition of material in equally sized layers of alternating green and brown material acts as a handy rule of thumb to ensure the correct balance is achieved. Building a heap in this way over just a few days will almost certainly result in a 'hot heap'.

In reality, the waste arisings of the average household may not be produced in sufficient quantities to allow layering to be carried out. This does not need to be a problem. Instead of using layers to measure equal volumes of greens and browns, why not just balance each bucket of kitchen waste with a bucket of cardboard or straw for example. In fact, because the bacteria in the compost need both greens and browns to prosper, the closer together these two types of material are, the better.

One other thing to bear in mind is that a layer of twigs or branches at the bottom of a compost bin or heap can be a great way of helping to achieve a vertical flow of air through the material.

Do I have to turn the contents of my bin regularly?

As with the conventional wisdom regarding layering, this technique has its roots in the large compost piles traditionally associated with keen gardeners or large gardens. It involves literally turning the whole heap over in order to open air spaces in the material and to reduce compaction. This can be quite discouraging to people who either do not have the physical capability to lift large volumes of material, or do not wish to spend a lot of time composting.

Air is essential for the survival of the microbes that degrade organic waste and help to turn it into compost. Although turning the heap is the best method to ensure there is sufficient air, there are a number of easier methods. The first is to mix the material around in the bin using a garden fork or compost aerator. The second is to use a broom handle to poke holes in the material creating air channels. However, easier still is to ensure there is a good mix of materials in the bin that will help to create air pockets amongst the material. Materials that are particularly good for this purpose are those that provide structure in a heap, such as corrugated cardboard, egg boxes, the cardboard centres of loo rolls or kitchen rolls, scrunched-up paper, or a jumble of twigs and small branches.

I don't have anywhere to put my compost bin – what can I do?

This can be an awkward question that requires you to find out more about this questioner's situation. They may perceive there is nowhere to place a bin because they believe it will take up more room than it actually does, or that it must go in an out-of-the way corner, or perhaps because there is a limited area of soil available to stand the bin on. Therefore it is necessary to find out more about the composition of the garden – is it mainly lawn, concrete or very small?

The Garden Organic demonstration gardens show that in the case of a small garden, the compost bin does not have to be overt and it can be beautified; for example, with a screening of plants or through decoration by children. There are also compost bins available that are designed to be aesthetically pleasing, such as the 'Beehive' bin. If location within the garden is a problem, the questioner should be reminded that compost bin in the middle of the garden is more easily accessible than one at the end and is therefore more likely to be used.

Gardens that are predominantly concrete or stone present their own problems. Placing a compost bin directly onto concrete will produce compost eventually, but the composting process may be slowed down. This can be partly solved by placing some mature compost or soil in the bin. Another issue is that of liquid leaking from the bin as the organic material decomposes, which can stain a patio or other hard surface. To avoid this problem, emphasise the importance of a well-balanced mixture of greens and browns, with perhaps a few more browns than in the conventional situation to maintain the compost mixture slightly drier than is normally recommended. You could also suggest placing wood chips or layers of newspaper under and around the compost bin to soak up any liquid that does leak from it.

In some situations, particularly where there is only a small paved backyard that does not generate any green waste, it may be sensible to suggest the questioner uses a wormery rather than a compost bin. These tend to be smaller than compost bins and the worms can be fed on kitchen waste scraps and newspaper only. The resulting compost and liquid fertiliser can be used for containers and houseplants.

Should I use liquid compost activators?

There are two types of liquid compost activators sold in plastic containers at DIY stores and garden centres. One type contains a concentrated solution of readily-available nitrogen, and the other a solution of microorganisms and enzymes. Some people swear by liquid compost activators while others notice little effect. In a well-balanced compost bin these elements will already be present and proprietary activators should not be necessary; however, they may aid the composting process where the contents of the compost bin cannot be balanced, for example, where only a single type of material is being composted, or where materials are very slow to decompose such as woody prunings.

You could recommend some high-nitrogen compounds that can be produced at home for no cost and that will work very effectively as compost activators. Fresh grass clippings are high in nitrogen, as are nettle leaves, comfrey leaves and coffee grounds and these can all be added straight to the compost bin. If desired these materials could also be steeped in water to obtain a liquid activator, but advise caution regarding over-wetting the heap. The most readily available compost activator is human urine. It is high in nitrogen and trace minerals and has been traditionally added to compost heaps for centuries.

Can I empty the vacuum cleaner contents into my compost bin?

As most household dust is comprised of human skin particles, most of it will decompose. However, the synthetic fibres found in many modern carpets will not decompose and will be present in the finished compost. The biggest problem is that vacuum cleaner dust is very dry and may soak up moisture from the compost bin, disturbing the balance. So the answer is yes, but if possible soak the vacuum dust well first if it is being added to the bin in large quantities.

Should I drill air holes in my compost bin?

Composting is an aerobic process, which means air is vital to ensure effective decomposition. The presence of air in the bin is much more dependent on the structure and mix of materials in the bin than the presence of air holes. Therefore, drilling holes should not be necessary as long as the structure allows air flow, for example through the use of scrunched up paper and cardboard, or twigs and prunings. If the materials mixture is too compact, holes in the bin will not be sufficient to facilitate airflow to the centre of the bin where composting activity is often at its highest and thus requiring more oxygen. Additionally, lots of air holes in the sides of the bin may let out valuable moisture as well as letting in air.

What can I do about flies in my compost bin?

The flies you get in a compost bin are very small fruit flies that live on fruit and vegetable waste in the bin, rather than large bluebottle type flies (which are only attracted by meat, fish and dairy which must not be put in a compost bin). To reduce the number of fruit flies present in the bin, you could recommend keeping a small bucket of soil beside it and sprinkling some over every time fresh material is added so that it is covered. Alternatively, spread a couple of sheets of newspaper or a flat packed cardboard box over the top of the pile, again so that the fresh material is not immediately on top of the bin.