Six simple rules for worm farms

Worm farms should be kept cool in summer and warm in winter.
Worm farms should be kept cool in summer and warm in winter.
Vermicast (worm poo) is black gold for your garden, says Ben Elms. Photos supplied.
Vermicast (worm poo) is black gold for your garden, says Ben Elms. Photos supplied.

A healthy worm farm is not rocket science, but it does require a little upkeep, writes Ben Elms.

On my rounds as Dr Compost, I get to talk to people all over the district about the composting they do at home. The number one complaint I hear is the failure of worm farms.

''Where did all my worms go?'', ''My worms just disappeared'', ''I killed all the worms'', ''The only things I'm farming are fat rats and mice'' ... I could go on and on with the quotes but with plenty of beeped-out expletives.

Worm farming isn't highly technical, but worms do require a little care and attention to keep them happy and eating your food scraps.

One of the biggest problems I find is the amount of food scraps getting out of synch with the growth of the worm colony. It goes something like this.

One day you get excited about starting composting. You want to keep food scraps and green waste out of the bin where they smell, and therefore the landfill where they can create methane and contribute to global warming.

You've decided a worm farm is the way to go. So far so good. You acquire a worm farm, either home-made or a store-bought model. The excitement builds and you introduce the worms. By now, you're almost frothing at the mouth.

Yes, worms can be that exciting. Finally, it's time to put your first food scraps in. Yeeha. Every day you take out more food scraps, and add them to the scraps already sitting in your worm farm.

The problem is, our friendly tiger worms are just settling in and they can't cope with the mass of food raining down on them. Tiger worms need time to settle in, increase their numbers and eat their way through the feast you're providing.

Once up and running, say after three months, your worm farm should be full-steam ahead. So in these first few months, hold back on the food.

You could consider using a parallel composting system to complement your worm farm (like Bokashi buckets) or you can just dig the food scraps straight into a trench in your vege garden while the worms play catch-up.

Starting with a good number of tiger worms at the beginning speeds the whole thing up. Half a kilogram of tiger worms is fine, 1kg is better.

Not all worms are equal when it comes to worm farms. We use tiger worms (Eisenia fetida) here in New Zealand. They're different from earthworms as they've adapted to eating decomposing organic materials. You will rarely find them in the soil.

They prefer environments like a compost heap, a rotting straw bale or a pile of horse manure. Earthworms will often find their way to a compost heap but they don't have the same efficiency and effect as tiger worms. Vermicast (worm poo) is black gold for your garden.

You can use it anywhere and plants will love the biological goodness you are giving them. Add it to homemade seed-raising mixes, or use a handful when planting seedlings or as a side dressing for established plants and trees.

Dilute the vermiliquid (worm wee) 10 to one and use as a drench or foliar spray. The results will speak for themselves. Good luck and happy worm farming.

Ben Elms (aka Dr Compost) gives advice and runs workshops as part of the Dr Compost project to encourage home composting and reduce waste. He will be running composting workshops in Wanaka on May 2 and Queenstown on May 3. Visit for more details.

Keep your worms happy

Don't overfeed.

Try strip feeding: place today's food next to yesterday's food and so on. Worms are less active in the cold winter months so feed them less then. Don't feed them citrus, onion peelings, liquids, oils or milk.

Chop up your food scraps.

Worms have small mouths. The more surface area the better. The happiest worms I've seen were fed the juicing pulp from a fresh juicer.

Try a little lime.

Once a month, add a sprinkle of lime to keep the pH in balance.

Little white worms everywhere can mean it's a little too acidic, so add some lime. If there are heaps of them, try adding some white bread then remove the bread and white worms the next day.

Don't fry or freeze your worms.

In summer, shade is good, a sunny spot works in winter. Place your worm farm under a deciduous tree or move them as it gets cold. You can chuck an old blanket or duvet over the farm if you get frosts.

Damp not wet

Keep an eye on moisture levels. The worm farm should be moist but not wet. Hotter times may require a light water sprinkle from time to time. If your worm farm has a perforated lid and is outside, cover it if you live in a rainy area.

Keep pests out

If you get little black midge flies (fruit and vinegar flies), cover the worms with an old damp tea towel or hessian sack. Rats and mice love worm farms, make sure yours is vermin-proof. Set traps if required.

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