What is worm farming?
Compost can be produced using worms. This is known as worm farming. It is also called ‘vermiculture’ or vermicomposting. Usually tiger worms are used for worm farming in NZ, though red worms can also be used.
Worm farming uses the same principles as composting, but it does not generate heat, making it cold composting. Value is added to the materials when they are eaten and excreted by the worms. This produces what is called vermicast, or casts, and worm tea which have high levels of nitrogen, phosphorous and potassium (NPK) compared to ordinary soil. Casts are valuable for plants’ leaf growth, root and stem strength and flower and fruit set.
Additional benefits of worm farms
- Casts and worm-tea are fantastic for plants (always dilute the worm-tea to the colour of weak tea – usually about 1:10).
- Kids enjoy them.
- If you have mostly kitchen waste and live in a home with little or no outdoor space, a worm farm is a good option.
Choose a site which is sheltered from sun, wind and rain. Carports or sheltered porches are ideal. Use a layer of bedding first– eg, hay/ coconut fibre/ shredded cardboard/paper. Bedding should be damp and porous. Add worms – 1000(250g) is fine; 2000 is even better.
Food can then be added. You can cover food scraps with damp newspaper or cardboard to limit flies and odour.
Worms can eat their own weight each day but don’t overfeed at start (eg, for 250g of worms give about 200g of food. Worms need air but not light (worms are photophobic).
Keeping it going
Worms need a moist environment. Check that their surroundings are damp, add water if needed. Add dry leaves or torn up paper products if it is too wet – the working area should be as damp as a wrung out sponge.
Add food scraps regularly, smaller pieces (no larger than 2cm) will be eaten more quickly and prevent odours.
Worms cannot tolerate very hot or cold conditions (10-30° is ok). Small flies or white worms/bugs indicate the worm farm has become too acidic and you should add a sprinkling of lime to neutralise pH. Worms are omnivores and will eat almost anything, but some things are best avoided (keep reading for more information). If worms are overfed, uneaten food will rot.
The worm diet
What worms like
- most fruit and vegetable scraps
- coffee grounds and teabags
- aged horse manure
- dirty paper
- crushed eggshells
- vacuum cleaner dust
What worms don't like
- spicy food, chili, onion, garlic
- meat and milk products
- flour products
- large amounts of cooked food
- garden waste
- shiny paper
- citrus / very acidic food
Harvesting your worm casts
After a few months or when a layer is full, you should harvest the casts. Remove the top layer and take off the bottom layer. This bottom layer contains the casts. It is ready when few worms can be seen. Remove any worm tea from the bottom level. (When using, dilute to the colour of weak tea, usually about 1:10).
When one working layer is full, you can add another layer to your worm farm. Place new layer on top of the old one and then add bedding (paper/ straw/manure) and then add more food scraps. Add food only to the new layer. The worms will migrate slowly to the food layer.
If you have large layers in your plastic bin and you want to harvest casts earlier, you could add a layer of chicken wire instead of a new plastic layer.
For worm farm stockists, refer to the Council's subsidy coupon. Download the compost subsidy coupon (750KB PDF) or call the Council on +64 3 546 0200.
Common worm farming problems
If you are having problems with your worm farm, check out these common issues and solutions.
Problem: rotting food
Too much for population
Problem: Fruit flies or small white bugs and worms around farm
Cover food with damp paper
Add lime to increase pH
Problem: worms climing up sides; worms fat and pale
Add paper products and dry leaves, gently fork holes in the working layer
Too dry or acidic
If worm farm is on legs, place each leg in a container of water
Problem: Food rotting and not eaten
Too much food, wrong food or pieces too big
Add less food, break into small pieces
Problem: No worm tea
Not enough water
Types of worm bins
There are different types of worm bins but most have a number of layers. It is easier to harvest worm casts from bins that have more shallow layers. Bins generally have two to three layers; some bins can have extra layers added to increase capacity. When buying a bin, ask the retailer whether there is any back up if you need advice.
- A tray/layer/stacker system allows for easy removal of worm casts.
- Bins with taps allow the worm tea to be extracted easily.
- Some bins stand on legs which can be easier to proof against pests (legs can stand in bowls of water if need be)
- Some bins are made from recycled plastic and made locally
- Sizes vary and costs vary between $20 and $200
- Worms and food scraps are added to the top working tray which generally has a vented lid
- More levels can be added once the first working tray has filled with worm casts
- A three-tray system allows for easy removal of worm casts with minimal loss of worms
- Size, price and functionality vary a lot, so ask questions and think carefully before you buy!
Make your own worm bin
You can easily make a worm bin out of large buckets, polystyrene trays or an old bath. If you use a bath, remove the plug. If you want to, you could build a frame to allow the bath to sit securely at waist height.
Bricks, posts or blocks may be used for elevation, and for stability, ie, 100-150mm height (allowing room for the liquid collection container placed beneath plug outlet).
The plug outlet end must be no less than a 5 degree fall to the lowest point to achieve adequate drainage. Roofing such as ply or corrugated iron will be needed to shed water and provide protection from summer sun. Place into the base of the bath 1.5m of 65mm perforated drainage pipe with two layers of old stockings. This seals the ends and covers the perforations which stops the pipe blocking.
Add pumice sand or scoria to a depth of 75mm then place shade cloth, doubled over and cut to fit, on top of filtering layer.
A free-draining fibrous matured compost is ideal given that it is not going to produce heat. Dampened shredded corrugated cardboard and lunch paper give increased air availability and reduce the risk of bedding material heating up. You need to water well and leave at least two
days. Then check for temperatures over 25 degrees. If there are any unpleasant odours, apply two handfuls of garden lime and mix in.
Only apply old lawn clippings. Fresh clippings heat up and cook the worms. For quick results, 500g-1kg (2000-4000 worms) should be enough for your worm farm to cope with 400gms to 800gms of mixed food waste each day. This volume will increase as the worms multiply. Spread worms on to bedding and spread food scraps in one area and rotate feed sites.
As the bath fills use garden fork and loosen bedding; this increases air circulation and reduces bedding compaction.
To remove the casts, once the worm farm is full (after nine to 18 months), place a plastic sheet or large container next to the bath, and using a garden fork remove the top half of the worms’ bedding. This is undigested food and is where the majority of worms will be. Place this to one side and remove all casts.
Rinse the drainage layer thoroughly catching all liquid. Replace the contents that were put aside and commence the feeding, forking, watering process when required. Your bath worm farm will ultimately digest about 1-2 litres of mixed organic waste a day.
Question and answers
How many worms do you need to start a worm bin?
1,000 is ok, but bin takes some time to get going; 2,000 worms (500g) will get a worm bin working much more quickly and efficiently.
What food can and can’t go into a worm bin?
Worms like a diet of fruit and vegetables with 30% of their diet being carbon. (Carbon material can be provided in the form of scrunched up envelopes, handee towels, tissues, shredded paper; any paper that’s not shiney and coloured or has a plastic film coating is ok). Worms don’t like citrus, bread, meat, onions, garlic, excess kiwifruit or large amounts of grass, leaves.
What do I do if there are lots of fruit flies?
Add a decent sprinkling of lime and wait a day or two. If you stiil have flies in your bin, add more lime and carbon material (eg, paper or dried leaves).
Do I need to lime my worm bin?
A small handful of lime or gypsum once a month helps to keep the food sweet.
What do I do if I go on holiday?
Add to the bin as follows.
- 1 – 2 weeks, empty out your fridge of any fruit and vegetables
- 2 – 3 weeks, dried grass or coconut fibre from garden centre or worm grower
- 4+ weeks, coconut fibre block from garden centre or worm grower
How much do I dilute the worm ‘tea’?
Worm tea is very high in nitrogen and needs to be watered down to about 1:10, or so it’s the colour of weak tea. The liquid is so rich that it can be harmful if not diluted.
What can I do with the worm casts?
Worms casts can be mixed with potting mix, seed raising mix and compost (about 20% casts to 80% mix), and is the perfect medium into which to plant seedlings, plants and trees. Casts do not have to be diluted for use in the garden, but make sure they are tilled into the soil. For best results, add compost and mulch as soil cover.
If you would like more information on this or other forms of composting, download the handy Create Your Own Eden 'how to' guide for composting, worm farms, and Bokashi from the Create Your Own Eden website, or call Council on +64 3 546 0200 for a copy.