Making a compost bin

A compost bin can be made from a wide range of materials. Whatever you choose must be durable, a good insulator, and allow air and moisture in to help the composting process.

A compost bin is simply a container used to hold compost. It can be made of any durable and rigid material and it helps if it is a good insulator.

Unless you want the bin to blend into part of your garden, your best bet is to use the cheapest materials available. However, the design is important to get the best from your bin.

Size and Shape

It is easier to build a square or rectangular bin.   Before you build a compost, please check the permitted size on the BRAA Regulations. Many of the plastic bins sold for making compost are round. This means they have a smaller surface area than square ones of similar capacity.

If a bin is too small, the outside surfaces of the materials inside will turn into compost very slowly because conditions are not right. The smallest size that will work well is one about one cubic metre. If you need a larger bin, consider building a double or triple version, as shown below.

Having decided on the materials, shape and size of your bin, remember to allow for moisture and air to penetrate.

Successful Composting

If you let your compost dry out or becoming waterlogged, composting will stop. The ideal moisture content is about 50-60 percent.

A cover is useful to keep the rain out by unless you are prepared to water your heap in dry weather, you will need to prevent moisture from escaping as well. A square of old carpet or sacking will help  to retain moisture and heat.

It is best if the bin is open at the bottom and stood on free-draining soil, or the compost at the bottom can become sludgy. You can also start the heap with a layer of twigs of course material to aid drainage. If your bin is open, try and put it somewhere shaded and out of the wind. A good mixture of plant material will contain enough water to keep the composting process going. It may tak some trial and error to balance water loss with the need for aeration.

Design Refinement

A double bin is useful because it makes turning the compost heap much easier – you simply fork it from one compartment to the other, mixing and aerating it. Another way of using double bin is to fill one half while the other is maturing. Id you have space (and the quantity or garden water to fill the bins) you could build a deluxe three-compartment bin – one section being filled, a second maturing ad a third ready for use on the garden. Instead of keeping your compost bin in one place you could consider moving the compost bin each year. Position it on a part of the garden you know is lacking in nutrients or where you want to out a special plant. The soil will then benefit from the seepage of water and nutrients ad the increased worm activity. Next year, move it to a new site.

When constructing a bin, consider how it will be emptied. You don’t want to demolish it to get the compost out and you may want to remove it and turn it to increase the aeration. So make the bin with a removable side.

Soil Contract

Contact with the soil is important to allow worms and insects to enter the compost during the final stages. It also helps with drainage. For this reason, some of the compost material should touch the soil, or be fairly close to it. Standing a bin on concrete is not a good idea.


Most gardeners do not have enough compostable material to fill a bin completely to one go. It is a good idea to keep suitable waste dry, for example in plastic bags, until you have enough to make a layer at least 15cm deep. If you add material in large quantities, you will have a chance to mix different materials effectively.

Compost Activators

these are worth using only when you have loads of tough waste and not enough soft stuff, like grass clippings, to mix it with. Activators contain nitrogen which helps boost decomposition. Try sprinkling dried blood, sulphate of ammonia fertilisers or a thin layer of fresh manure. It’s also worth ‘inoculating’ a new heap with compost from an old one as this will introduce the micro-organisms responsible for decomposition.

Turning the compost

Air is essential for efficient composting. if you use a slatted wooden bin or wire cage, air will find its way into the compost but it may dry out the materials near the sides and the compost will cool down. Rapid composting at the centre of the heap soon uses most of the available oxygen, too.

The best way of aerating compost is to provide ventilation from below – as the bin heats up air will be drawn through by a chimney draught effect. A gap or aeration layer at the base will prevent the bottom of the bin becoming waterlogged by allowing excess moisture to drain away.

For faster results, experts recommend turning the pile of compost at least once a week. Your reward for this effort can be compost within a couple of months in the summer. However, a lot can be achieved by turning the compost just once after about ix weeks. This makes sure all the material is composted evenly.

When is it ready?

If you intend to dig the compost into your soil, it’s usually best to wait until the compost is well rotted and you are able to identify any of the original ingredients. It should be dark and crumbly and have a pleasant ‘earthy’ smell.

Compost used as a mulch doesn’t need to be quite so well rotted, although it will look far more attractive if it is.

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