Home Composting 101: Worm Farming

This week is Compost Week. So in this three-part blog series, we’re digging into sustainable, garden-loving ways to deal with food and plant waste at home or in your workplace. 

After starting with Bokashi, we’re taking a look at worm farming, before we investigate home composting. While each method has its pros and cons, there’s sure to be a method that suits the people, available space and waste output in your household.

In a worm farm, tiger worms or red worms live on a mix of food scraps, garden waste, and paper products. (Read on for the optimum mixture.) In return, the worms produce soil-like worm castings and worm tea, which is a great liquid fertiliser when diluted at least 1:10 with water. Both are great for feeding your garden.

There are many brands of worm farm available in New Zealand, but they all fall into two basic categories: ‘stacked’ and ‘continuous flow’. A stacked worm farm consists of stacked frames (usually two) that you fill with food, and a sump below with a tap to catch and pour off the liquid that drains down from the stacked frames.

A continuous flow model doesn’t have layers, but uses gravity, and the fact that you only feed from the top, to keep the worms in the right place. This type tends to hold a bigger volume of worm castings and food. It also has a tap and a release at the bottom to let you access the worm tea and castings.

Whatever type you’re using, a worm farm will thrive (and not smell) with the right balance of ‘greens’ and ‘browns’. Greens are full of nitrogen, and green matter is usually soft and fresh, like salad leaves, for example. Their high nitrogen content means they will rot, putrefy and become quite smelly if they are not balanced out with some browns, which are mainly carbon. Browns tend to be brown, dry and brittle, and rather than rotting quickly, they take a much longer time to break down in a worm farm.

The best balance to feed your worms

70% greens: most fruit and vege scraps, eggshells, tea bags, coffee grounds, vacuum cleaner dust (from natural fibre carpets), poop from small herbivores like rabbits and Guinea pigs, dry autumn leaves.

30% brown: torn up, wet paper, cardboard and egg cartons, dry ‘browned-off’ grass clippings.

Don’t feed your worms: onions, garlic, chilli, milk products, pasta or bread, cooked food, citrus fruit or peel, oils. Dog or cat poo, if you want to use your worm castings/tea on a garden that is used for growing food, or if they have been wormed in the last few months.  (A very small amount of meat is ok in a large, thriving population of worms, but they don’t like fat.)

Winning with your worm farm

  • The best site is cool, shady and sheltered – try your worm farm under a carport, on a sheltered porch or under wide eaves
  • Use a layer of bedding – like coconut fibre, shredded paper, hay etc that’s damp and porous to get your worms started.
  • Worms can eat their own weight each day and will breed in response to a healthy environment and a plentiful food supply. Around 2000 worms can munch through half a kilogram of food each day, so slowly build up food levels, and cut up large pieces to make them easier for the worms.
  • Worms hate light but need air – putting a layer of damp wool carpet or blankets, newspaper or cardboard gives them a moist dark environment.


To have a worm farm is to play a ‘long game’. How much food it can process depends on the number of worms. It can be up to a year before your bin is full and you can use a nice pile of worm castings to work into the garden or grow seedlings in. In the meantime though, you will get a plentiful supply of worm tea to use on your garden.

For heaps (pun intended) of great information about choosing a worm farm, getting set up and troubleshooting, visit the Hungry Bin or Compost Collective websites.