Composting myths exposed

Along with old wives tales and gardening folklore, there are many myths about the right and wrong way to compost. Here we set the picture straight!

There should be holes in the sides of 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.

A compost bin is a hot bed for breeding slugs that will then eat my lettuces and courgettes

Slugs and snails are the number one enemy of many gardeners and some people believe the compost bin is a hothouse for slug and snail reproductive activity, creating massive populations that will invade the garden and devour the precious plants. Slugs and snails are decomposer organisms that help break down the organic matter in the compost bin so the bin acts as a great feeding ground for them. There is no guarantee that the slugs and snails will not be tempted to other areas of your garden, but the compost heap provides them with an ideal habitat they have no reason to leave as they have a constant food source and are protected from predators - they keep moving up the bin to get to the fresh material, and eventually die of old age. Some slugs live only on rotting organic matter and so will have no desire to leave the compost bin in search of living greens. Some people worry that when they spread the finished compost, they will spread around slug eggs; however, it is likely these will be predated on in the compost bin or will decompose as they become compressed within the heap.

If you do have slug problems, the most effective way to control them is to encourage natural predators such as hedgehogs that love to hibernate under compost heaps or piles of woody prunings left to decompose, so do encourage people not to have too tidy a garden and certainly not to get rid of their compost container!

Finally, on no account should slug pellets or other molluscides/insecticides be used in compost, as they will kill the benefical organisms that carry out the composting process.

A compost bin/heap MUST be built in layers

It's not true that compost must be built up in layers - 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.

I should 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 have to have more than one compost bin

Whether or not you need more than one compost bin will obviously depend to some extent on the amount of waste you are producing and also on how enthusiastic a composter you are.

Many keen gardeners have at least three compost bins so that they have one bin they are adding to on a regular basis with fresh material, one full bin that is being left to compost, and one bin of matured compost that they are using as and when required. Having more than one bin helps if you want to create a 'hot' heap - filling the bin all in one go with a good mixture of material will provide a sufficient volume of material for high temperatures to be created. Going through this the hot phase of composting that means weed seeds and pathogens are more likely to be killed and compost is produced more quickly than 'cool' composting. However, this is not a practical option for many householders, especially if they do not have a large garden or do not produce much garden waste, and great compost can be produced with only one compost bin that is added to gradually.

Depending on the size of the bin and amount of material that is put into it, it may well be that the material at the bottom of a compost bin is ready for use while there is still room to add new material at the top. If the compost is brown, smells earthly sweet and you can no longer recognise the materials you put in, then it is ready. This material can be removed through the hatch at the bottom if it is large enough. Alternatively, you can take the bin off completely, find a new location for it, and place the undecomposed material from the heap you have exposed back into the bin. The decomposed material could then be used on the garden, or left covered up in a small heap to mature for longer if necessary.

I can't put many grass cuttings in my compost bin

Some grass in a compost bin is good because grass is an activator and will speed up the breakdown of organic materials. In contrast, adding large quantities of grass can result in a smelly, slimy mass. Many householders find that their garden waste is restricted to grass cuttings and that it is difficult to properly balance this with other materials. One option is 'grass-boarding' where thin layers of grass are layered between torn up cardboard. The result can be excellent compost, which is weed-free and does not contain large particles or lumps of material.

If grass-boarding is not an option, there are some other uses for grass cuttings:

  • As mulch - this works better if you put newspaper around your plants first, and then cover with a layer of grass cuttings; this can then be replenished each time you cut the lawn
  • An addition to leaf mould - if you made leaf mould in the autumn then you can mix equal volumes of grass to the leaves throughout the following summer. This will speed up the breakdown of the leaves and increase the nutrient content
  • Leave it on your lawn - this will add nutrients to the soil, and provided you mow regularly thatching should not occur. It is possible to buy mulching mowers, which are specifically designed for this purpose

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