One alternative to a compost heap is a worm bin. This is a small-scale composting system that employs worms to digest food and plant materials. A nutrient-rich material is produced that contains decomposed organic matter, bedding and worm castings (manure), which will enrich your garden. Worm composting is also called vermicomposting.
A worm bin uses tiger worms to convert kitchen vegetable waste into highly nutritious liquid and solid plant foods.
Tiger worms are able to tolerate a range of temperatures from 0 - 35 degrees C and will eat almost all organic household waste including cooked and raw vegetable and fruit scraps, paper, cardboard, tea bags, coffee grounds, egg shells, hair and even contents from your vacuum cleaner bag.
Since tiger worms do not have teeth, they must wait until the natural action of soil fungi and bacteria have partially broken down the food material to a usable form. Tiger worms are not keen on citrus or onion skins, but will eventually eat these.
Vegetables and fruits contain around 80% water, so is not normally necessary to add water to your worm bin.
As the worms eat the food, liquid is released into the bin and this gradually filters into the bottom collecting-tank.
This is the liquid-vermicast or leachate and is a highly nutritious plant food. It MUST be diluted 10:1 before you water it onto your garden. It is very safe to use on delicate houseplants too.
When your bin is working near its maximum capacity you should get around a litre of this leachate per week. It keeps very well and has no offensive odour.
As the worms digest the food they will begin to form a dark rich compost called vermicast in the base of the bin.
This is also a very nutritious plant food; it is very stable and safe to add to seedlings, houseplants and your general garden.
Use a wooden, plastic or metal container: some suggestions are an old bathtub, wooden box or plastic bin. Commercially made worm bins are also available from some garden centres and the Warehouse.
The bin should be about 20 - 40cm deep, 40cm wide and 40 - 60cm long. Shallow bins allow better air-flow, and since worms live near the surface, deep bins are not required.
Good drainage is essential: drill 8 - 12 holes, 1cm diameter, in the bottom of the bin for drainage and air circulation. Raise the bin on bricks or wooden blocks. Place a tray underneath the bin to catch liquid - this is an excellent plant food, dilute 1 part to 10 parts water.
A worm box can be set into the ground, without a bottom. This will still need a lid with aeration gaps. The worms will stay below the area of feeding. The holes in the lid should be small (1 - 2mm) in diameter and sufficient to provide aeration but avoid problems with flies. An old window flyscreen makes an excellent first lid. Another lid is also needed to keep out the rain and sun.
The worm bin should be placed in a convenient position away from the full afternoon sun and with some protection from heavy frosts in the winter.
Use moist shredded paper, peat, straw, aged manure or mature compost. Don’t use sawdust or chicken manure.
Loosely fill three quarters of the container with moist bedding. Add 1 or 2 handfuls of coarse sand or topsoil to provide grit needed by worms to grind food.
Two species or worms are especially suited to composting; these are tiger and red worms (also known as red wigglers or manure worms).
The worms can be brought from worm farmers, some garden centres or collected from other compost heaps, horse stables or manure heaps.
Add to your bin 250gms (500 worms) to 1kg (2,000 worms). Add some vegetable scraps. Be aware that it will be some days until bacterial activity has made these scraps suitable for the worms to eat. Next, cover the worms with a piece of wet carpet cut to the size of the bin, wet cardboard or wet sheets of newspaper
The worm population should double every 40 days until the optimum population is reached.
Now replace the lid on your worm farm and let the worms do their job. They are sensitive to the light and will burrow down if the lid is removed.
Feed sparingly until your population of worms has built up. As the worms begin to multiply you may see the eggs in the bedding material. They are about the size of a match head; coloured dull yellowish-brown and each egg will contain approximately 4 worms.
Worms will eat anything organic but have preferences. It is easier to mention their dislikes: they will leave citrus and onion skins to last.
Food such as tea bags, coffee grounds, tissue paper, even human hair, can be added. Untreated wood ash and egg shells will help to regulate the pH (acidity level). As a general rule never add more than 10% of the food supply as one type of scrap material.
The smaller the food particles, the faster it can be ingested by the worms. Worms ingest food only after soil fungi and bacteria have started decomposition. It takes approximately 2 weeks for the fresh food to become available to the worms.
Meat, fish and dairy foods have the potential for smells. Moist crushed paper should be added regularly to aid aeration.
Lawn clippings are high in fibre and produce heat if fed directly - this can kill the worms. However this material can be composted first and added when the heating process has stopped, if insufficient food scraps are available.
Feeding levels are in direct relationship to the weight of the worms in the bin. Worms can eat up to their own weight in food per day.
Over many months, vermi-cast will reach the top of the worm bin. It is dark brown and soil-like. You will need to harvest the compost and replace with new bedding to keep the worm environment healthy. Otherwise worm castings will build up to a level that is unhealthy for the worms.
At this point you could add a second working bin on top of the first bin. The food in the lower tray must be able to touch the food in the second tray, so the worms can make their way across into the new bin. Begin to add scraps to the top working bin. The worms will begin to feed in the top bin and once this bin is approximately three quarters full of vermi-cast, most of the worms will have moved up into it.
The bottom bin can now be removed and harvested for your garden.
Alternatively, if you don’t want to add another bin, remove and keep aside the top 15cm of material (this is where the worms are). Harvest the worm compost beneath then add extra bedding to replace the harvested compost.
Worm castings can also be harvested by flushing 1 litre of water through the top bin six weeks after you have set up the worm bin. Do this every two weeks. The worm castings are water-soluble and can be collected in the leachate.
The vermi-cast can now be used on the garden (1cm deep), in seedling trays (3 parts compost to 1 part castings) or for your house-plants. It can be used in its solid form, or water may be added to form a thick liquid additive.
Worms may be harvested from your worm bin should you wish to share your tiger worms with another gardener, or start another worm farm of your own. Worms may be harvested after the population stabilises. This has occurred when very few egg capsules (bright yellow ones) are observed, around 3 - 6 months after establishing the worn bin, depending on the temperature.
Be aware that worm compost/vermi-cast is very rich - use sparingly! Use small amounts to:
topdress container plants, add into potting mixes or fertilise soil when planting. Mix 1 part vermi-cast to 4 parts bark, compost, mulch, peat or soil.
The leachate, or “worm-tea” should be diluted 1 part to 10 parts water before watering plants.
Be careful not to add worms to potted plants. Worm bins don’t generate heat like compost heaps, so be aware weed seeds may still germinate.
If you wish to decommission your worm bin, the contents (including the worms) can be put into your compost heap or garden.
Worms will feed at a faster rate once they have adapted to any new food source. Worms will also eat more if their food is mashed, blended or processed.
Controlling temperature to around 24°C will improve the overall performance of your system.
Worms will leave very acidic food such as onions and orange peels until after they have eaten their preferred foods. A handful of garden lime (or crushed oyster shells or ashes from a fire) every few weeks will help to balance the effect of acidic foods.
The regular addition of worm fattener will encourage stronger, fatter worms. Since they consume up to half their own body weight each day, the fatter they are the more wastes they will eat.
Worm-fattening recipe
Chicken layers pellets 50%
Wheat or corn flour 10%
Powdered whole milk/skim milk 10%
Bran or wheat meal 20%
Agricultural lime or dolomite 10%
Mix the ingredients and sprinkle lightly on the food wastes about once a week. After several months you will have fat, tough worms (in ready supply for fishing.)
Not recommended. The worm farm is designed to break down soft organic waste. Slow composting organic wastes such as garden refuse are best dealt with by conventional aerobic composting methods. Click here for information on home composting.
If you worm bin has been recently set up, the worms may be still eating the bedding material. Be aware food scraps first have to decompose before worms can ingest them. This takes about 2 weeks. Nor will the worms consume much until their population increases to optimum, which takes several months.
Food scraps are about 80% water, which is released as the worms break them down. This will tend to stay in the bedding for a long time before eventually draining out. Any dry material such as old manure, newspaper or cardboard should be pre-soaked before being added. It is important to keep a moist sack, carpet or wet newspaper over the freshly added food to encourage the worms to move up to the surface to feed. This will provide a dark damp shelter for them.
Watering your worm farm will enhance the production of liquid fertiliser. If you pour a maximum of 2 litres of water over the covering and scraps each week or two and then place the empty bucket under the open tap, you will have a constant supply of liquid fertiliser. The sudden ‘flood’ will not harm the worms as long as the drainage is good.
Only if you have a thick surface layer of mulch in your garden. Compost worms require moist conditions all year round because they don’t tunnel deep like earthworms to find moisture. If you cannot provide this environment in your garden, don’t introduce compost worms into it.
There are several possibilities:
Bedding could be too dry / wet, too much disturbance by curious fingers, too much light – was the lid left off? Too hot: move to a shadier spot, and do not add green lawn clippings.
The worms can return to the working trays themselves up the ramp, but if you want you can help them.
These are enchytraeids. They are not harmful, but their presence indicates bedding mixture is too acidic. Add a small amount of rock lime / garden lime, wood ash (untreated) or egg shells to raise the pH.
These are vinegar flies. They are particularly fond of pineapple, tomato and other fruits. A small handful of lime and a top cover of plastic or wet carpet underlay will deter them.
Flies shouldn’t be able to get into your worm bin. Should you experience any influx of maggots, they will most likely be the soldier fly or vinegar fly larvae. The soldier fly larvae grow up to 2cm long, starting out white but soon turning dark grey with distinct ribbing bands. Fishermen say they make great bait.
The vinegar fly larvae are small, usually 6mm in length or less. Don’t be too alarmed if they appear. They are actually beneficial to the waste breakdown. If you want to remove them though, do so by liberally applying lime, or placing bread soaked in milk on the surface of the compost. Larvae love bread and should infest it. Remove the bread after 2 - 3 days and dispose of it.
Ants will enter your worm bin, particularly if you have let the bedding become too dry or acidic. Add water to raise the moisture level and add a liberal quantity of garden lime to where the ants are gathering. This should discourage them. If they persist remove them physically and smear some Vaseline around the legs or place each leg in a container of water to isolate the system.
The only smell associated with a well-maintained worm bin is a pleasant rainforest odour. If it has an offensive smell, it is an indication that anaerobic bacteria have built up in the system in uneaten food wastes.
Stop feeding the worms and stir the wastes in the top tray lightly with a garden fork adding garden lime as well. This aerates the organic material and allows worms to move through it more easily. Repeat this aeration procedure regularly to prevent reoccurrence. Start feeding again when all smells are gone.
Leaving an established worm farm for 3 - 4 weeks without constantly adding food is not a problem. Just feed the worms a good quantity of food waste 5 - 10cm deep before you leave. Make sure that you leave the unit in a cool place under cover and leave the tap open with a container under it. Putting well-soaked newspapers on top of the scrap layer will give added protection against the bedding drying out.
For further information contact: Environmental Health, Gisborne District Council, telephone (06) 867 2049.