How to Make a Simple Worm Bin from Free Materials

When you grow your own food, compost is always at a premium. Moisture retention, planting, mulching, seed compost, top dressing - you can never have enough of the stuff, and if you're like me you try to compost as much of your kitchen waste as you can. However, there are food items that you can't put in a regular compost bin 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.

Last year I made up a simple five-tyre worm bin which was entirely free to make, and it's eaten all the food waste from our family of four very successfully (with a little help from the chickens). Yesterday I broke the bin down to empty it, and split the active vermicompost (worm compost) to make two new bins, which will cope more easily while conditions are cold and will give me a little spare capacity in the summer. So, here's what you do.

Materials list:
Large paving slab (or use pre-existing hardstanding). Freecycle is always full of them.
Five used car tyres. Any local tyre dealership will be amazed you want them.
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.

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.

Pack the rims of the tyres loosely with "brown" composting material.

The packing provides a low-nitrogen, high-oxygen bedding area for worms that are not feeding. You can use dead leaves, hay or unbleached shredded paper, which has been dipped in water and allowed to drain. In the photo below I have used spoiled straw, simply because I had some to hand. Put the largest tyre in the middle of the base to form the bottom of the bin.

Load the bottom tyre 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 coccoons, 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.

Use your smallest tyre at the top, if you have one. 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!

Add the 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 bungy 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 bungy is hooked into two U-shaped pieces of strong wire which are pushed between the tyres, but I could just as easily have run a bit of bamboo through the middle of the bin and tied a length of baling twine from one side to the other.

And that's it, you're done.

A caveat; concerns have been raised about the possibility of toxins including selenium and volatile organics leaching out of tyre rubber, and this is something that you might want to consider. However, so far as I have been able to make out the problems with tyre rubber are associated with disposal, and through the creation of rubber dust when driving; the actual tyres themselves are pretty inert even when exposed to ultra violet light. A project to study the feasibility of tyre-chip field leach systems in New York State found that

• Leaching under conditions operative in leach fields does not contribute concentrations of semi volatile or volatile organic compounds that are of concern for groundwater protection.

• Leaching under conditions operative in leach fields’ results in higher metal concentrations. Of the metals measured in the leachate, iron and manganese were found in the highest concentrations. Although elevated over that measured for stone, the concentration of both iron and manganese were typically below secondary water standards.

This leads me onto the subject of where I stand on the whole notion of organic food production, something I'll cover in a later article.

Coming up - using your worm bin!

*One easy way to do this might be to dig out a shallow trench at the lowest edge of the base slab, and place a length of guttering topped with chicken wire (to keep out leaves and debris) into it. This could then run into a buried jam jar, and provided the gutter and exposed sections of the slab were screened from rainwater by leaning pieces of board, the worm liquor would collect in the jar. I will be trialling this in the Hollow as soon as time allows.

Obligatory cat picture!