Worm farming at home
Notes prepared by Kat Lavers, May 2024
Worm farming is a great way to reduce your household waste and produce a high quality organic fertiliser that will keep your soil and plants healthy and productive. They’re fun for kids too!
Setting up a worm farm
- Position your worm farm in an area that is cool with full shade in summer, but ideally has some warmth and sun in winter, with convenient access from your kitchen. Under a deciduous tree is often a great spot.
- Add bedding material from your kit, or a 10cm layer of compost or soil. Keep this layer very moist.
- Add at least 1000 compost worms, ideally per person in your household for a faster start. Empty the worms on the surface and they should quickly burrow out of sight if they are in good condition.
- Start by feeding very small amounts of food, waiting until it is almost gone. Under good conditions your worms can double their population every few months, but it usually takes 6 months for a home worm farm to process large amounts of food waste. Note that households producing lots of food waste may need more than one worm farm.
Keeping your worms happy
Food
Worms will eat most fruit and veg scraps, tea leaves and coffee grounds. Eggshells, avocado skins and pips are fine too, but they take longer to break down and may be present in the finished castings. Citrus, onions, garlic, meat, bread, dairy, fatty and salty foods should be avoided, but experienced worm farmers can add small quantities to a well-established worm farm.
Add food to surface of bedding in thin layers (<3cm). Start by feeding a small handful of food and note how long it takes for the worms to eat it. Build up slowly and aim for food to be processed within a few days. Smaller pieces will break down faster. Worms will eat roughly their bodyweight in a week, but remember that if you are starting with 1000 worms this is only around 250g!
Worms need a balanced diet, so along with your nitrogen-rich food scraps you should also regularly add handfuls of carbon-rich materials such as moist shredded paper, cardboard, straw or autumn leaves. Placing these on top of your food scraps will reduce odour and deter flies.
Temperature
The bedding in your worm farm (ie. the material the worms are living in) must remain between 0-35ºC or your worms will die. Worms are most effective at decomposing your food scraps when their bedding temperature is between 15-25ºC, so keep your worm farm in a cool area with full shade in summer, but winter sun is useful to keep them
Moisture
Worms prefer very moist conditions – around 70-90% moisture, which is a few drips of liquid when you squeeze a handful of bedding. Worms will try to leave or die if their bedding becomes too dry. Often the moisture in your kitchen scraps is enough, but you may need to moisten dry materials like paper or leaves. Also make sure your worm farm can drain properly.
Air
Worms need to breathe just like we do. Over time the bedding and castings in your worm farm may become dense and compacted, which can also inhibit breakdown of food scraps and become smelly. Occasionally fluffing up the bedding with a trowel, garden fork or compost screw will keep your worms happy and productive.
Protection
Birds and rodents love a juicy worm snack, so a tight lid is important. A damp woollen blanket, folded newspaper or hessian sack will keep the surface humid and dark, and encourage your worms to feed on your food scraps.
Troubleshooting
| What you notice.. | ..and what to do |
|---|---|
| Foul smells | A smelly worm farm indicates overfeeding, unsuitable food, lack of oxygen and/or lack of carbon materials. Remove uneaten food, aerate bedding, add carbon-rich materials such as shredded paper, cardboard, straw or autumn leaves. A light sprinkle of garden lime, dolomite or wood ash watered in can help too. Stop feeding until smells disappear. |
| Vinegar flies (tiny flies hovering around the worm farm) | Vinegar flies indicate overfeeding or feeding too much of the wrong foods. Act fast as they can quickly build up populations. Follow actions for ‘Foul smells’ above. Stop feeding until vinegar flies disappear. A damp hessian sack, woollen blanket or whole newspaper laid on surface of bedding helps too. Make a vinegar fly trap by mixing ¼ cup apple cider vinegar, ¼ cup water and 2 drops dishwashing liquid in jars and positioning in and around worm farm. |
| Worms not eating scraps fast enough | Check that you are adding the right foods, and moisture and temperature of bedding is correct. You can speed up your worm farm by starting with more worms (ideally 1000 per person in household), chopping large scraps into smaller pieces and keeping a damp hessian sack, woollen blanket or newspaper on the surface. Be patient when starting as it can take around 6 months for populations to build up. |
| Worms massing in large clumps on surface | Usually indicates overheating – especially during heatwaves but also possible if food scraps are heating up. Act fast or your worms may die. Remove food, aerate bedding to release heat, water if bedding is dry, and place a frozen container of water on the surface. Always keep your worm farm in a cool area with full shade during summer. Larger, in-ground or insulated worm farms are more resilient in hot weather. |
| Small white worms | Despite internet rumours these are actually baby compost worms. They usually appear in largest numbers in spring and autumn, and are a sign of good conditions in your worm farm. |
| Ants nesting in worm farm | Ants are not necessarily a problem but can indicate that your worm farm is too dry – check moisture of bedding. They may also be attracted to sweet or protein-rich foods. |
| Beetles, mites, slugs, slaters etc | Don’t worry about other critters – diversity is a good thing! All these creatures have important roles to play in decomposition. |
| Worms are escaping! Eek! | Check that food, temperature, moisture and oxygen are correct. It is normal for worms to hang out on the lid and go exploring during wet weather. |
Harvesting and using worm farm products
After a couple of months you should notice a build up of dark brown castings (worm poo). Many commercial worm farms have layers that (at least in theory) allow you to separate worms from castings as they migrate into a new layer looking for food. You can also feed worms on one side for a while and harvest from the other, harvest from the bottom where there are fewer worms, or empty worms and bedding into pile in the sun and scrape away the surface gradually as they move away from light. To use castings you can:
- Mix castings into top few inches of moist soil and mulch well in hot weather to keep beneficial microbes alive.
- Dilute leachate from your worm farm (worm juice/tea) or mix a handful of castings in a watering can until the colour is like weak tea and water your plants.
Worms will regulate their population according to size of the farm and available food, so you can also harvest worms to give away or feed animals when they are well established.