Second Prize for a Biological Garbage Disposal Unit

In Autumn 2000 I wrote an article for Organic Gardener magazine about worm towers. For years I thought the idea had sunk without a trace. When our daughter moved to a little flat in Brisbane we helped her build a garden with them. It worked so well that it crossed my mind occasionally, I wonder why that idea never caught on?  Maybe I should write about it again in Witches Kitchen.  Then a couple of years ago a worm farmer popped up at our Farmer’s Market selling worm towers and I was so excited to see the concept in production with someone else. In the last little while I keep seeing examples of them everywhere.

This is the article as it was originally published (complete with my dodgily drawn bmp image).  It worked brilliantly, built just like this, for our daughter’s little garden at a Brisbane unit block.

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Remember those electric garbage disposal units that they used to put in sinks in the Dark Ages of ecological awareness?  They were obscene – noisy, dangerous, and wasteful – but they did have their attractions.  There are moments when you could almost be forgiven for thinking they weren’t such a bad idea.

Like when you come home after dark and the kitchen scrap bucket is chock-a-block and moving, and there are a couple of container gardens in the fridge.  Or when the neighbour’s dog decides to excavate last week’s spaghetti from your compost pile.  Or when the health inspector spots a very fat brown rat heading in the direction of the compost bins.

Compost is wonderful stuff, but, especially in urban situations, it has its drawbacks. It takes so much work to make that you practically have to grow lettuces made of gold to justify its labour cost. And it is often difficult to get hold of enough ingredients all at once, especially animal manure or high carbon ingredients like hay.

Kitchen scraps on their own do not make good compost. The thermophyllic bacteria that are responsible for real compost like more carbon in their diet.  They like a situation that is drier and has more air, and they need a cubic metre or more all at once to conserve enough heat to breed well.

What people mostly call compost is really a slowly rotting pile that loses much of its nitrogen to the air in the form of a nasty smelling gas, and feeds noxious critters along with good ones like worms and slaters. The only place for it is the far end of the garden, which is why fantasies of a whirring thing in the sink arise when you are confronted with a full scrap bucket on a cold, dark night.

My nomination for first prize for biological waste disposal units is a well designed moveable chook pen, or “chook tractor”. It will take any kind of kitchen waste, including prawn heads, cooking oil and chop bones.  It takes very little work.  It doesn’t breed smells, flies or vermin.  It produces chickens to cuddle, or to eat, eggs, scared insects, and fertilizer, and it puts the fertilizer right where you want it.  It’s a hard act to follow.

But before I get too lyrical, there are situations where a chook tractor is not the answer.  If you go away frequently, if you have a very small garden where space is at a premium, or if you have a rampant neighbourhood dog pack, for instance.  In these situations, red manure or tiger worms are a close contender.

This design is for a waste disposal unit that uses worms to automatically fertilize the highest priority garden beds – the small “green pick” beds close to the house.  It satisfies the permaculture principle of serving at least three different purposes:  It disposes of kitchen scraps without work, smells, flies or rats.  It turns them into fertilizer and it puts the fertilizer where you need it.  And it breeds the worms right in your garden beds, where they will improve soil structure and aeration with their worm holes.

This design lends itself very well to adaption, substituting recycled or locally available materials and scaling it up or down.  So the first instruction is to read the instructions and think about how you can change them to suit your own needs and resources.

The closest site to your kitchen door where you have around ten square metres that has some kind of soil (it doen’t have to be good soil) and gets at least a little bit of sun is the spot for this project. Proximity is the most important criterion.  On a cold, dark, preferably rainy night, take the kitchen scrap bucket and see how far you enjoy going with it. That’s your site.

Lay out six small garden beds about 1.4 metres in diameter, edging them with old bricks or something similar.  Cover the paths between them with cardboard to smother weeds, and then with something nice to walk on like sawdust or wood chips.

Next you will need a six metre length of 225mm plastic stormwater pipe, available from any big hardware, plumbing, or recycled building materials centre.  Cut it into six one-metre lengths (a hacksaw or a power saw with a metal cutting disc is the tool) and drill a lot of large holes in the bottom 40 cm of each length.

In the middle of each bed, dig a hole and bury a pipe up to the 40 cm mark, so that it stands 60 cm out of the ground.  Put a shovel full of soil back into it so that on the inside it is filled to within about 20cm of ground level.  The holes that you drilled should start just below ground level.  You should be able to reach the pipe easily from outside the bed.  If not, make the beds a little smaller, or make them a bit kidney shaped.

Put an upturned plant pot or an icecream container over the top of each pipe as a lid.  Water the area well, put a good handfull of worms on the ground next to each pipe, and cover them and the rest of the area inside the edging with a thick layer of mulch.  You can buy red manure or tiger worms from most garden centres or by mail order.  A couple of thousand is a good starting population for this project.

Empty your kitchen scrap bucket into each pipe in turn.  It should be literally a 30 second job.

Red manure worms will eat most things.  You may need to build up a population before you try them on prawn heads though.  And while the odd citrus peel is fine, if you juice oranges for breakfast every morning, they will boycott munching their way through that quantity.  They like a dietry supplement of calcium, so keep a bag of lime in the kitchen cupboard and add a couple of desertspoons full to each bucket of scraps.

Once the population builds up a bit, the worms will take only a few days to demolish a small bucket of scraps, so the level inside the pipes should never rise much above ground level. If you have a big household, or you have other sources of kitchen waste, you may want to either use more pipes, or something bigger, like pickle barrels.

These beds are perfect for the annual herbs like parsley, dill, coriander and basil, and the salad greens like leaf lettuce, rocket, celery, kale, and endive. They are expensive and difficult to buy really fresh, so they are the highest priority for growing.  They are best picked right when you are ready to use them, so they need to be as close as possible to the house.  And they benefit from the high levels of nitrogen in these beds.

Adding one or two taller plants to each bed improves the aesthetics and disguises the pipes.  Cherry tomatoes, perennial capsicums, chillies, eggplants, and broccoli or flowers like dahlias, zinnias, cosmos or snapdragons are all suitable.