Recycled crate wormery
A DIY wormery made from recycled crates

If you’ve got a small garden then you might find it difficult to find space for a conventional compost heap. A possible solution is a worm compost bin, which takes up far less space because an army of worms does most of the composting work.

Worm compost bins come in different forms. Some look like small wheelie bins, with taps on the bottom. Other designs use stackable trays, and if you’re handy you can even make your own. The features they all have in common are that they are enclosed to keep the worms in, have air holes so that worms can breathe, and a tap to drain off liquid. A worm bin that lives outside needs a lid to keep excess rain off, but most bins have lids anyway as worms prefer to live in the dark.

The worms used for composting are sometimes called red wigglers. They are a native British species, but they’re not earthworms. They don’t build burrows in the soil, and they love eating organic waste – which is why they are ideal for worm bins. On a good day a composting worm can eat its own bodyweight in waste. It may not sound like much, but even a small packet of worms holds around 1000!

You can buy composting worms in fishing tackle shops (because they’re also used as bait), or mail order. Once you have them you need to settle them into their new home with some suitable bedding. Coir compost is often used, but shredded newspaper is fine too. Make sure the lid is on tightly, to keep the worms in as they explore, and try to avoid the temptation of lifting the lid to check on them too often.

The next day is the time to start feeding your worms. They like eating all kinds of kitchen waste – vegetable peelings, mouldy fruit, cooked fruit and vegetables, tea bags and leaves, coffee grounds and kitchen paper are all fine. Don’t add too much food in one go, as it will rot before the worms can eat it, and start to smell. Over the next few weeks your worm population will gradually increase, and you can start to add more food at a time. Try wrapping food waste in newspaper before you add it to the bin, to help prevent flies. After several months the worm population will be large enough to eat all your kitchen waste, and will then stabilize.

Don’t add meat or dairy products to your worm compost bin, as they smell as they rot down. You also need to avoid anything too acidic – too much onion waste, or citrus peel. You can add eggshells or garden lime to counter the acid and keep the worms happy – they don’t like acidic environments.

A worm compost bin creates a lot of liquid run-off, which can be used as a plant feed. It needs diluting about 10:1 with water before use, so that it’s roughly the colour of weak tea. Every six months or so you will be able to remove a small amount of finished worm compost. It’s highly nutritious stuff, so use it to feed hungry plants or as part of a potting mix for houseplants.

Handy tips:

  • In summer, worm bins can get too hot – put them in the shade, or in the garage/ shed.
  • In winter, worm bins can freeze – bring them inside or insulate them with a breathable material.
  • Worms can drown if the tap clogs up and the liquid level rises, so check it whenever you add waste.

Now what?

There’s plenty more about compost, including how to use it once you’ve made it, in The Peat-Free Diet.