Worm composting is an efficient method of turning kitchen waste and small amounts of garden waste into nutrient-rich compost and a concentrated liquid fertiliser. However, it is not a substitute for conventional composting.
Timing All year round
What is a wormery?
A ‘worm bin’ or ‘wormery’ usually consists of at least two compartments; a lower collection sump for the liquid and an upper composting area where the kitchen waste goes in and the worms actively work. However, single compartment wormeries can be also used.
The worms used for composting are known by various names; brandling, manure, red or tiger worms. These include the species Eisenia foetida, E. andreii and Dendrabaena veneta. Composting worms live in decaying organic matter, whereas earthworms are soil dwellers. They are smaller and darker red than the common earthworm, Lumbricus terrestris, which is unsuitable for using in worm composting.
Starting a wormery
A wormery is relatively easy to establish though a few points need to be considered.
- Worms are most active in warm moist conditions, ideally between 18-25ºC (64-77ºF)
- Their activity noticeably declines below 10ºC (50ºF) and above 30ºC (86ºF)
- A wormery should be kept in a shed or a sheltered area of the garden where it gets neither too cold in the winter nor too hot in the summer
- If thinking about keeping wormeries in the kitchen, utility room or on the balcony, consider that when neglected they can sometimes produce odours
- Composting worms prefer a pH of between 6.5-7.0, and well-ventilated conditions to live in
- They will not tolerate extreme acidity and dislike being waterlogged because this restricts their supply of air
Using your wormery:
- In the bottom, place an 8cm (3¼in) layer of moist ‘bedding material’ such as old compost or coir if it is provided by the supplier. This creates a humid layer in which the worms can burrow and begin to digest their food
- Add the composting worms
- Cover with no more than 8-10cm (3¼-4in) layer of kitchen waste
- Leave for about one week to allow the worms time to settle into their new environment
Feeding the worms (adding waste):
For best results, add small amounts of waste often to the wormery.
- Chop the waste into smaller pieces so it can be eaten faster
- Place the food on the top of the compost
- Alternatively, bury the food within the compost to create feeding pockets
- If the waste is not being eaten, feeding should be stopped for a few days until the worms start to work through the top layer of the composting material
- Avoid adding more waste than the worms can cope with
What to compost
Worms enjoy a varied diet eating any decaying organic matter. You can put in;
- Any raw vegetables, except for onions, shallots, leeks and garlic that are best used in small amounts or cooked first
- Any cooked vegetables
- All fruit, except citrus peel, which needs to be limited or preferably cooked before adding
- Tea bags, eggshells, coffee grounds and small amounts of bread
- Limited amounts of newspaper, shredded office paper and cardboard, but not glossy magazines
- Small amounts of garden waste such as annual weeds, leaves and other soft green material
Remember: Fruit and vegetable scraps that contain seeds can be included but the seeds may germinate in the wormery.
What to avoid:
- Dairy products, fat, grease, meat, fish and bones as these are likely to attract unwanted pests and flies
- Larger quantities of tough leaves and woodier material as it will slow the system down
If there is a lot of garden waste, which could overload the wormery, it is often best to have an ordinary compost heap as well.
Organic waste usually has a high moisture content. If the lid is kept on, dry conditions are unlikely to occur. Add water only if the wormery appears dry.
An established wormery can be left without the addition of food for up to four weeks. However, the liquid may accumulate which needs to be drained off to avoid waterlogging.
Occasionally fork the compost over gently with a hand fork to check that the worms are present and healthy.
Ways to increase the rate of composting:
- Aim to provide and maintain the desired temperature especially during the winter months
- Add extra worms (see below for suppliers) to the existing population
- Avoid overloading the wormery with waste
- Wormeries with a greater surface area will also work faster
- Using worm compost and liquid
Emptying the wormery:
Wormeries are usually emptied when they are full; this takes about 8 to 12 months. You must separate the worms before using the compost.
The worms tend to congregate in the area just below the top layer of food waste. Simply remove the top 20cm (8in) layer and use it to restart the wormery again.
Alternatively, if the weather is warm and dry, spread the contents of the wormery thinly over a polythene sheet. Cover the centre of the compost with layer of wet newspaper. As the compost dries, the worms will move towards the cool, moist compost under the newspaper from where they can be collected. Once emptied, and the worms separated, the wormery can be filled with a new layer of bedding, the worms returned.
Many wormeries use stacking trays for the worms to work up through. The finished compost is in the bottom tray and can be removed. The tray is then emptied and returned to the top of the stack. This makes sorting the worms unnecessary.
Worm compost and liquid – how to use:
The worm compost can be used as a general soil conditioner or as a constituent of homemade growing media. It is generally rich in nitrogen and potassium.
The liquid drained from wormeries can be used as a liquid fertilizer on garden plants after diluting with water at a rate of 1 part liquid to 10 parts water. Its nutrient composition will vary.
Some wastes have strong odours, which can attract flies (termed fruit flies) that are harmless, but can be a nuisance. This problem can be avoided by burying the new waste in the decomposed material or covering it with a layer of damp newspaper. Do not use chemicals to control the flies as it could harm the worms.
If too much waste is added for the worms to cope with then the wormery may start to smell. This could also attract flies and possibly vermin. Remove and dispose of excess or undigested food. Wait until the worms start digesting the top layer of food before adding further waste.
Another reason for the wormery producing unpleasant odour is if it becomes too wet. Drain off excess liquid and add some shredded paper or card to absorb excess moisture and increase air circulation. Check if the worms are alive. Dead worms can be a problem especially when left unattended e.g. during holiday breaks. Make sure that the wormery has drainage holes.
If you improve drainage but the smell persists, the conditions may have become slightly too acid for the worms. To correct this, apply a small dressing of calcified seaweed or calcium carbonate (garden lime, ground chalk or ground limestone).
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