How to build a worm farm to help your garden and the environment

Caring for critters does take a bit of commitment but, as a starter pet, worms are pretty low maintenance.

They don't need walking, they only need feeding once a week or so, and instead of having to pick up their poo, you'll be able to use it to fertilise your garden.

It's also a great way to teach children about natural recycling, and to reduce the amount of rubbish going in your bin.

You can buy a purpose-built worm farm from nurseries or you can make your own — extra brownie points for using recycled materials that would otherwise go to waste, such as when Costa from Gardening Australia made one in an old bath.

But first up, it's important to earmark a protected, shady spot to place your worm farm so they are at a constant temperature, because they will literally cook if exposed to full sun.

What you'll need to build a worm farm:

• Three polystyrene fruit boxes plus one lid (pick ones that are the same size so you can stack them; at least one needs to have no holes in the bottom)
• Newspaper
• Shade cloth offcut (large enough to cover the bottom box)
• Some mushroom compost or coconut coir
• Compost worms such as tiger worms (Eisenia fetida) or, in warmer climates, Indian blues (Perionyx excavates) (do NOT use earthworms)

Method for starting a worm farm:

Whether you're using a purpose-built kit or making your own, the set-up is the same.

Stack three boxes on top of each other; the top two are feeder boxes where the worms will live and these need holes in the base, while the bottom container forms the reservoir for the liquid worm "tea", so needs to be waterproof.

It helps to have a tap on the bottom container so you can drain this off later, but if you're using a polystyrene box you can simply make a hole in one corner and put a bucket underneath, or plug the hole with a cork to control when you drain the liquid off. (This is liquid gold, so don't discard it; see uses below.)

The worms start off in the middle container.

Place the shade cloth over the bottom reservoir box to stop the worms falling through and drowning. Put the first feeder box on top and line it with a couple of sheets of newspaper plus some bedding material such as cow manure, sawdust or coconut fibre. Then add the worms!

You can buy a box of worms from your local hardware store or perhaps start off with just a handful from a friend's worm farm, but make sure you use composting worms that live on the soil's surface, not earthworms that live deeper into the soil.

Spread them out over the bedding and cover with damp newspaper or damp hessian. A polystyrene lid is a good idea too.

Let them settle in for a week or so before you begin feeding them. Keep an eye on their appetite as they grow and breed; if you find there is still a lot of food left a week after feeding them, you've given them too much, and if it's all gone in two or three days they need more!

The number one trap new worm farmers fall into is overfeeding, so check them often until you get a feel for your worms' needs.

As the middle section slowly fills with castings (worm poo), the worms will want to move up. This is when you need to set up the second feeder box for them to move into; entice them up with some fresh food and allow two to three days for them all to follow.

You can then remove the first box, which is full of worm castings, and use this on the garden. The "top" box now becomes the middle level and the emptied first box can go on top. Keep switching them over as this process continues.

Feeding your worms

Under ideal conditions, compost worms can eat their body weight in food every day, but overfeeding will result in a rancid, smelly mess, so wait for at least half of their last "feed" to disappear before adding another thin layer, and make sure to include an equal amount of ripped-up, non-shiny paper or moist egg cartons with it; this helps keep the system aerated and gives the worms a balanced diet.

There are a few foods to avoid, including anything acidic (citrus, pineapple, garlic and onions), oils, spicy foods, and food that will smell when it starts to go off, such as dairy products, fish and meat.

What worms DO love is pre-chopped food, slightly aged food (especially when it's strong, such as coffee grounds), and ground-up egg shells, which aids the worms' digestion.

Worm farm maintenance

In dry weather you may need to water your worms — the bedding should be damp but not soaking wet, like a squeezed-out sponge.

The temperature of the worm farm should ideally stay between 12°C and 28°C. Polystyrene boxes help regulate the heat, but your worms may still need an old blanket over them on frosty nights, and a moist hessian sack over them or an ice block wrapped in newspaper to keep them cool on hot days.

If you need to go on holidays for a week or two, give your worms a good covering of old straw (if it's been used for animal bedding then even better) to provide food and shelter while you're away.

After about three months you should have some castings to harvest.

Using your worm gold

Both the worm poo (worm castings) and worm "tea" are great for gardens.

The worm tea is an excellent organic fertiliser, but is best watered down first; mix one part tea to 10 parts water. Use it to feed pot plants or your veggie patch. If the liquid smells bad, it could contain bad bacteria and juices from the food, so pour it through the system again.

The worm poo is a great soil conditioner and slow-release fertiliser. Add a small amount to potting mix and garden beds, or water it down to make a liquid feed. To do this, add enough water to make a slurry then put a couple of handfuls of slurry in a bucket and fill it with water.

This mix can be used anywhere on garden beds and lawns, where it will help increase your plants' drought tolerance and will also make more nutrients available to them.

Fun worm facts:

• There are three main types of earthworms: ones that live on the surface and eat decomposing organic matter; soil-eating ones that form horizontal burrows in the top 10-30cm of the soil; and ones that create permanent deep vertical borrows and visit the surface to find leaves and other plant food.
• Australia has 650 known species of native earthworm (but potentially 1,000 unknown species) and about 80 introduced species, including most garden earthworms. Some Australian worms live in deserts and others can be found in trees; however, many cannot survive the changes to the soil made by clearing vegetation and adding fertilisers. You often need a microscope to spot the difference between worm species.

• Earthworms die if cut in half but some worm species can regrow lost segments.
• Worms need to stay moist; if they dry out they will die, but they can drown easily too.
• Earthworms take about a year to grow to full size and can live up to eight years.
• Worms breath through their skin, they have a brain and five hearts. They don't have eyes but they can sense light and will try to bury deeper into the soil to avoid it.
• Worms are hermaphrodites; they have both male and female reproductive organs.
• Most worms are pink, although the bright yellow canary flatworm can be seen on forest floors in Victoria and Tasmania, and big blue earthworms up to 2m long are found in Far North Queensland.
• Some tropical Australian worms leave trails that are bioluminescent — they glow in the dark.
• Worms can get worms; many carry parasites.
• The giant Gippsland worm is one of the longest worm species in world. It can grow up to 3m long and measure 2cm in diameter! However, it is listed as endangered because farming has reduced its habitat.
• Industrial worm farms are used in the USA to process scraps in hospitals, prisons and shopping centres. Researchers in the Pondicherry University in India found worms were effective in removing heavy metals including lead, zinc, copper, cadmium and manganese from rubbish.