Compost bays on the allotment

Build at least two wooden bays of about a cubic metre each, on bare earth, and turn the heap from one into the other. Expect compost in six months to two years.

An allotment makes a lot of green waste. Turn it into compost and you've got free mulch for next year, which matters if you're going no-dig.

Bays or bins?

A compact plastic bin is fine for a small garden. On an allotment, the RHS suggests a large wooden bay, such as one built from pallets.

Size matters. Bins smaller than about 1 cubic metre are generally less efficient than bigger ones. A bay roughly 1m wide, 1m deep and 1m high is a good target.

Two bays or three?

Keen composters often run several bins in a row, so each one holds compost at a different stage. On a plot, that usually looks like this:

• Two bays: fill one while the other finishes. When the first is full, turn it into the second and start again.
• Three bays: one filling, one rotting down, one ready to use.

If you're short of space, two bays are plenty to start with. You can add a third later.

Where to put them

• On bare earth. Standing the bay on soil lets worms and other soil life in and lets it drain. If it has to go on a hard surface, put a few spadefuls of soil in the bottom first.
• Near where the waste comes from, and where you can get a wheelbarrow in.
• Where your site allows. Check before you build. Some councils need permission for structures. Bolton, for example, asks for written permission before sheds and similar go up. Ask whether compost bays count on your site.

Filling and turning

Mix soft green waste with dry brown material, and don't let any one thing dominate, especially grass clippings. Compost needs air and moisture to work. Our greens and browns guide goes through the mix in detail.

Turn the heap several times a year if you can. If that's too much, fork through or stir it every few months. Moving it from one bay to the next is the easy way to turn it.

Be patient. Compost takes between six months and two years to be ready.

What to keep out

Some plot waste spreads disease if you compost it at home:

• Blight-infected potato and tomato material. The RHS says it should go to council green-waste collection or be burned, because blight's resting spores can survive home composting.
• Brassica roots with clubroot. Clubroot spores can stay in soil for up to 20 years, and you don't want to spread them on to clean beds.
• Onions, garlic or leeks with white rot. It spreads in contaminated soil, and its resting bodies last at least 15 years.

If your site doesn't allow bonfires and has no green-waste collection, ask the committee what other plot-holders do with diseased material.

Using it

Use finished compost as a mulch on beds, or dig it in. It's the backbone of a no-dig plot.

FAQs

How big should an allotment compost bay be?

About a cubic metre or more. The RHS says bins smaller than 1 cubic metre are generally less efficient.

How long does compost take on an allotment?

Between six months and two years, depending on what goes in and how often you turn it.

Can I compost blighted potato leaves?

The RHS says no. Send them to council green waste or burn them, as the spores may survive home composting.

Your next step

Check your site rules, then pick a spot on bare earth near your beds and build the first two bays. Our greens and browns guide covers what to put in them.