When you grow your own food, compost is always at a premium. Because it is rat-proof, a simple tyre stack worm composting bin allows you to compost even things you couldn’t put in a regular composter because of the risk of attracting vermin; bread, rice, meat, fish, dairy, and anything that has been cooked. In the winter, even raw food scraps may tempt rats to move in, leaving you no option but to throw good organic material away: if you’d rather not, a worm bin may be for you.
One note of caution: old tyres may be free, but using them in your plot cannot be considered organic. Zinc and other chemicals have been shown to leach out of ‘crumbed’ tyre rubber and, although the risks for whole tyres are thought to be much lower, those leachate chemicals will still be there in tiny amounts. If the thought of that worries you, this design isn’t for you. That said, a simple five-tyre worm bin is entirely free to make, and will eat all the bits of food waste that can’t go on a regular compost heap. So, here’s what you need:
- A large paving slab (or use pre-existing hard standing). Freecycle is always full of them.
- Five used car tyres. Any local tyre dealership will be amazed you want them.
- Some stiff wire, such as an old coat hanger.
- A bin lid, or similar. This is the tricky bit – keep your eyes open.
First, choose a level spot that will have some shade in the hottest part of a summer’s day. Unless you modify the design to collect the nutritious liquor the worms produce, then this will run into the surrounding soil – so it makes sense to place your bin in the shade of a deciduous tree.
Make the base
Put down a hard base such as a paving slab. This provides a rodent-proof bottom for the bin, and so needs to be big enough to make contact with the bottom tyre all the way round. Make sure that the slab is approximately level so that the bin does not lean, but allow a little slope for drainage.
Prepare the tyres
Pack the rims of the tyres loosely with “brown” composting material. This provides a low-nitrogen, high-oxygen bedding area for worms that are not feeding. You can use dead leaves, hay or straw, dipped in water and then allowed to drain. Alternatively if you’re re-building an existing bin you can use some compost from the old one. In these photos I used spoiled straw, simply because I had some to hand.
Build the stack
Put one of the tyres in the middle of the base to form the bottom of the stack, and load it with starter. This is a bucketful of material already rich in local composting worms, and there’s no need to pack it down as the action of the worms will do this for you. There are firms around who will sell you hugely expensive “starting packs” of worms or worm cocoons, but there is nothing magical about them and you do not get many; far better to ask a friend or neighbour for a bucketful of compost that’s just at the finishing off stage, when there are plenty of worms in evidence anyway. These worms are native to your area, and appear like magic when there’s work to be done.
Place the tyres in a stack, making sure it is properly upright. There’s no special reason for the stack being five tyres high, other than it makes it a convenient height for most people; you could just as easily use six. However, this won’t make the bin work any faster – that is governed by the number of worms, surface area, temperature and what you feed it with. You can always make a second bin!
Secure the top
Add a lid to the top, and secure it. An old bin lid is ideal for this since it has a handle to loop an old bit of bungee cord through, but whatever you use make sure that it is big enough to shed water away from the middle in a rainstorm. The lid needs to be secure to stop rats from pushing it aside, but a couple of bricks and a piece of board work just fine. The bungee is hooked into two U-shaped pieces of strong wire which are pushed between the tyres, but you could just run a bit of bamboo through the middle of the bin and tie a length of baling twine from one side to the other. And that’s it, you’re done.
A bin like this is fairly robust and the worms will put up with a lot – there’s no need to coddle it the way you would a smaller worm bin. Having said that, don’t add too much food at once (a two inch layer would be as much as the worms can cope with) and don’t put much citrus peel in because the worms hate it. Top the food off with a few handfuls of finished compost or topsoil. When you see worms roaming about on the surface, they’re ready to be fed again.
When the bin is eventually full, take the top tyre off carefully and keep it, and the compost in it, on a sheet of plastic while you empty all the rest of the compost from the other tyres. It should essentially be finished but may benefit from a bit of a rest, and should then be treated as a fertiliser for top-dressing or soil amendment, rather than as a growing medium: it’s just too rich to use neat. Finally, use the top tyre and the compost that was in it as your new bottom tyre and starter, and rebuild the rest of the bin.