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What to feed your worms

Compost worms benefit from a balanced diet. They will eat most normal kitchen fruit and vegetable scraps. Avoid feeding the worms large quantities of meat, citrus, onions and dairy foods. Some processed food also contains preservatives, which discourage the worms from eating it. These foods won’t harm your worms, but they will avoid them and those scraps will break down and rot in the bin. The worms will eat their preferred food first but like to have some variety. The smaller and softer the scraps, the easier it is for the worms to digest and process them into castings.

Compost worms will also eat garden or yard waste, and animal manure. If adding lawn clippings take care to only add a little at a time. Fresh lawn clippings can heat up and cause problems. If you do place animal manure in your bin ensure that the animals have not been treated with anti-worm medication, as it may still be effective in their dung!

It is also not advised to use dog or cat droppings if you intend to use the castings in your food garden, as the animals may have gut parasites, which can potentially infect humans.

How much to feed worms

• Add up to 2.5cm per day
• Uneaten food should not be more than 5cm deep
• Only add more food as it is eaten

It is very important that the hungry bin is not overfed. A fully functioning bin will have up to 3kgs (6.5lbs) of compost worms. They prefer to eat their food as it begins to decompose, but not if it has become slimy and smelly. If the bin is overfed, the food scraps will begin to rot before the worms can eat them. Rotting food scraps not only smell, but also interfere with the lifecycle of the worms and the operation of the bin.

Rotting food is anaerobic – or oxygen deprived. Because worms breathe through their skin, anaerobic conditions prevent the worms from breathing properly, and may cause them to die.

Worms can eat roughly their own body weight in food a day, so make sure that you only add about the same volume of food each day as there are worms. Start by feeding the worms a small amount of food each day. Each time you feed the bin, check that uneaten food is not accumulating. You could chop up large food scraps into small pieces – the smaller and softer the scraps, the easier it is for the worms to digest and process them into castings.

Slowly increase the amount you feed the worms as the population multiplies. The worms will breed and increase in numbers to match the food supply. Building up a full population of worms (about 3kgs) can take up to six months.

Remember the hungry bin is not the same as a rubbish bin. A garbage truck does not magically empty it every week! The worms cannot eat the food as fast as it is possible for you to put it in, especially if the population is small when you start. It is better to underfeed your worms than overfeed them.

A good rule of thumb is that uneaten food should be no more than 5cm deep. You can check this by digging through the top layer of the bin and checking how deep the uneaten food is. In a healthy bin finished castings should be present 5-10cm (2-4in) below the top layer.  You should also be able to see a mixture of adult and juvenile worms, indicating that the worms are breeding.  If uneaten food is building up, simply stop putting new food into the bin until the worms have eaten the food present.

Approximately 20cm (8in) below the surface the food should have been completely converted into worm castings. Finished castings look like high quality compost and have very little smell.

Worm eggs should also be present in the castings immediately below the food layer; signifying conditions are ideal for breeding. The worms need to be able to lay their eggs in fresh castings immediately below the food they are eating. If the bin is overfed and a layer of rotting food has formed, the juvenile worms will be unable to move upwards through the rotting layer to the fresh food when they hatch, resulting in the population declining.

To remedy a build-up of rotting scraps, you may need to gently fork a small amount of fibrous material into the top food layer. In extreme cases the rotting food will need to be removed completely and the bin restarted, as rotten food can take a long time to break down in the bin.