Dig a trench or hole that is between 300 and 500 millimetres deep, and place all of your kitchen scraps in it. You can add meat, dog manure and oily waste – just about anything. Cover the organic material with the soil, wait four weeks for it to rot down, and then plant over the top of it. The plant roots will soon be colonising the nutrient-rich zone of decayed waste and humus.
Left to Right: Trench composting is easy and labour saving. After covering the organic material and allowing it to rot down for about four weeks, you can plant straight over the top of the trench.
HANDY COMPOSTING TIP
Do not use coloured magazines in compost. The ink that is used to print the magazines contains zinc- and copper-based colouring agents, which, while harmless to humans, will result in the accumulation of excess copper and zinc in urban soils – which can be bad for plants.
In wet conditions or in heavy clay subsoils, conditions in your trench compost can become anaerobic. This does not stop the decay of the organic material or create bad odours, since the material is buried deeply, but it will prevent roots from colonising the decaying waste. Add a mixture of coarse particles, such as chopped straw, to ensure better aeration. Also, depending on the size of the trench, a covering such as a sheet of corrugated iron will help stop large vermin digging up the trench while initial decay occurs.
WORMS AND VERMICOMPOSTING
Worm farming is a very fast and efficient way of processing high-nutrient organic materials, such as kitchen scraps, that are regularly generated in urban areas around the world. Feedstock can be added to a worm farm on a daily basis if necessary, in contrast to ‘hot’ composting systems that start with a large ‘batch’ or volume of material, which usually cannot be added to once the composting process has commenced.
The worm population found within a vermicomposting system will ebb and flow in accordance with the amount of food available to it. If feed levels are gradually increased over a period of weeks, the population is able to expand reasonably rapidly.
Above-ground worm farming is also the perfect way to generate substantial quantities of liquid organic fertiliser, which can be used to liquid feed the urban farm in a sustainable way. The digestion process in the worm’s gut produces vermicast, which includes a lot of soluble nutrients and beneficial organic matter. The nutrients can be leached out, or the vermicast can be used to make a ‘tea’. Depending on the feedstock, a worm farm will usually produce a fertiliser that contains all the essential nutrients for plant growth in the right balance to replace those removed when we harvest our various food crops.
Worm farms can be used to generate worm ‘wee’, which is a perfect liquid feed for your crops.
In addition, as food moves through the gut of an earthworm, a complex range of beneficial microbes is added to it. Consequently, it has been claimed that if you use fresh worm liquid on your garden, it has the added benefit of acting as a probiotic for your soil as well. Whether the microbes in fresh worm liquid are any better than the vast microflora produced in conventional composting systems is open to debate until more research has been done on the subject. We prefer to think that the positive results obtained from using vermicast and worm-liquid preparations are due to the soluble nutrients and soluble organic compounds found within them as much as to the beneficial microbes that they add to soil.
CASE STUDY:
TOM’S COMPOST
The Mature Semi-thermal Compost table shows the make-up of mature compost from a ‘semi-thermal’ system producing only slight warming. The producer (Simon’s dad, Tom) has two plastic bins with lids but no bottoms, so both bins connect to the soil. One is actively composting a feedstock comprising dry and fresh leaves, mixed kitchen scraps, eggshells and lawn clippings, while the other contains more mature material that is colonised by worms, so it’s part worm compost as well. Tom doesn’t turn the mature material, as the healthy earthworm population does that job for him.
MATURE SEMI-THERMAL COMPOST
PLANT NUTRIENT ELEMENT TOM’S COMPOST
Nitrogen 2.28 per cent
Phosphorus 0.31 per cent
Potassium 1.61 per cent
Calcium 2.58 per cent
Magnesium 0.32 per cent
Sulphur 0.25 per cent
Iron 1580 mg/kg
Manganese 88 mg/kg
Zinc 245 mg/kg
Copper 45 mg/kg
Boron 30 mg/kg
The compost is very well balanced, although it has a relatively high level of calcium thanks to the eggshells. The NPK ratio is just about perfect. Zinc levels are higher than normal because Tom’s yard has been contaminated with zinc, which has probably found its way into the lawn clippings. This is not a problem, as zinc is not harmful to the health of humans or the worms – and his fig and mandarin trees don’t seem to mind it either!
Advantages of worm farming
One of the great benefits of the organic and liquid fertilisers produced from a worm farm is that the nutrient balance tends to be well matched to the needs of the food crops in the urban farm (assuming you’re feeding your worms the full range of food scraps from your kitchen). Essentially, you are returning the appropriate balance of nutrients back into your soil because you are feeding your worms scraps from the fruits and vegetables that were (mostly) grown in that soil to begin with, thus recycling the nutrients.
In larger, more commercially oriented urban farms, worm farming can be used to recycle the trimmings from the harvesting sheds, but in order to replace all the nutrients lost during the process of harvesting, it will usually be necessary to obtain additional organic feedstock from the farm and elsewhere. This could be manures, vegetable scraps from markets and retail outlets, and high-carbon sources such as wastepaper and sawdust, provided they are not contaminated.
Successful vermicompost uses a mixture of fine as well as open and coarse particles to keep the mass well aerated.
There are two distinct types of worm farms – above-ground and in-ground – but above-ground systems usually best serve urban farms. Above-ground worm farms are ideal where you want to extract high-quality liquid organic fertiliser for everyday use on the urban farm. In addition, the system will also generate significant quantities of solid fertiliser in the form of worm castings, but this occurs less regularly than the production of liquid fertiliser.
Above-ground systems are also better suited to larger commercial enterprises, where a constant and significant demand for fertiliser occurs. Again, these worm farms will usually require the addition of off-farm wastes to make up volume requirements.
Depending on the feedstock, a worm farm will usually produce a fertiliser that contains all the essential nutrients for plant growth in the right balance.
This clever proprietary worm farm is a hanging fabric bag with an opening at the bottom from which liquid and solids are collected.
Left to Right: Fresh food scraps are regularly added to the surface of this vertical above-ground worm farm.Pouring water over worm farms is necessary, especially for small systems that can dry out quickly. Any excess water can be collected as nutrient-rich leachate.
Operating worm farms
There are many different factors that must be dealt with when running a worm farm, including the amount of air and water in the farm, the ammonia and nitrogen levels, and achieving the correct temperature for optimum results.
Balance of air and water In our opinion, this factor is arguably the most important consideration for worm farms, as worms are particularly sensitive to drying out so they need a constantly moist environment, but also one that provides plenty of oxygen so they can breathe. There needs to be a range of particle sizes within the body of your worm farm; the larger ones hold the air for worm respiration, and the smaller ones hold the moisture that worms need to keep their skin damp.
If you have very wet vegetable scraps, add them to the worm farm along with dry material such as shredded paper, sawdust or dryish grass clippings – this will help reduce the moisture content and prov
ide aeration. Too much moisture in the form of waterlogging will drive the worms out of the worm farm; if such conditions develop, regularly add coarse organic materials, such as chopped straw or shredded cardboard, to the worm farm to provide the large particle size that creates extra air spaces.
Unpleasant odours emanating from your worm farm are always a sign of waterlogged, anaerobic conditions developing, which in turn leads to the production of gases such as methane and hydrogen sulphide (rotten-egg gas) that are toxic to worms. You will also often find pockets of the worm farm harbouring white maggot-like creatures that are displacing the worms – these are soldier fly larvae, and they thrive in very wet conditions. A good worm farm provides a refuge for worms to escape toxic conditions, such as a chamber or ledge above the composting mass, out of the sun and exposed to fresh air.
Ammonia and nitrogen The first product of decaying protein is ammonia, which is also the form of nitrogen excreted by birds. So, having too much meat and manure from carnivores (including poultry) in your worm farm will risk the generation of ammonia gas – which is toxic to worms. High-carbon products such as straw, paper and sawdust will absorb ammonia – so if you smell this gas coming from your worm farm, adding these products will help.
Some people say that you shouldn’t put meat in worm farms. However, provided you don’t add too much – and you also include some dryish high-carbon material to absorb the ammonia – this should not be a problem.
Temperature level Like humans, worms prefer to operate in moderate temperatures of 20–30°C. Worms generate their own heat, as do the composting microbes that unavoidably share the substrate with your worms. In summer, the worm farm can get too hot – when exposed to the sun at this time of year, the dark surface of a worm farm can quickly get up to 50°C by midday. To avoid this, insulate your chamber from the sun. You can also add water to the worm farm, increase the ventilation or make a smaller mass so that heat can’t accumulate. Again, always provide a refuge so that worms can escape the heat if necessary.
Cold slows the whole vermicomposting process, so insulation also helps here. Styrofoam (expanded polystyrene) is an excellent and readily available insulator. With windrow worm farming, it is always best to have a plastic cover on hand to preserve heat in winter, to exclude heat in summer and to prevent too much rain from waterlogging the windrows during the year.
TYPES OF WORM FARMS
Regardless of the size of your urban farm, there is a worm farm to suit your needs. Above-ground systems are the most popular, as they allow you to spread the nutrient-rich compost wherever you like around the garden, but in-ground systems are low-maintenance options that many people find very useful.
On-ground windrows
The simplest method of worm farming for larger enterprises is creating a windrow, where a long, tent-shaped pile is progressively built on a clean, weed-free surface of soil or something porous, such as polyethylene weed mat or shade cloth. The pile should not be so high that it starts thermally composting – making it 300–500 millimetres high and twice as wide usually works. One of the advantages of a well-constructed windrow, however, is that worms can move around to find a temperature that suits them.
As the vermicompost matures, worms will naturally head towards any new food waste that is added to the pile, but when harvesting the mature material it is often necessary to move worms to the vermicompost in progress. This can be done by scooping some or all of the worm castings from the windrow, and piling the material on a tarpaulin or plastic sheet that is in the sun. The worms don’t like light, so they will head down into the dark, cool, moist castings below. The top layer of castings can then be removed and used as fertiliser, and the rest of the castings with the worms can be returned to the windrow.
Windrows are the most common system used by commercial worm farms, as they have the lowest capital and running costs. Such enterprises usually make money from both sales of vermicast (and worm liquid) and from selling the worms themselves as fish bait or as part of worm-farm kits.
Like humans, worms prefer to operate in moderate temperatures of 20–30°C.
Commercial above-ground worm farms
There are many different worm farms available commercially, and each one has pros and cons. Stackable worm farms comprise a series of trays that allow the worms to migrate upwards; as they exhaust the food supply in the lower trays, they move up to reach the fresh food in the higher trays. After a few months, the bottom tray can be emptied of its castings, and any remnant worms are sorted out and put back into the system. The now-empty bottom tray can be rotated in the system to become the new top tray. In our experience with such systems, however, we find that gaps develop because the contents of the trays diminish in volume as the worms feed; this makes it almost impossible for the worms to migrate from a lower tray to the one above.
Invented in New Zealand, hungry bin (www.hungrybin.co.nz) is a worm farm that looks and functions like a giant vermicomposting funnel. It claims to be able to compost up to 2 kilograms of organic material per day; the material is simply placed into the top of the funnel, where the bulk of the worm population lives and feeds. As the material is broken down, it works its way down the funnel, along with any liquid that is produced by the worms. This liquid flows out of the mesh bottom and can be captured; there is a trapdoor to allow the harvesting of the worm castings, which are fully mature and ready to use by the time they reach the bottom of the funnel.
Another interesting above-ground worm farm is the Worm Habitat, manufactured in Queensland by a company called Worms Downunder (www.wormsdownunder.com.au). These units are made from modified wheelie bins, which are the standard rubbish bins given to ratepayers by many Australian councils. The wheelie bin has a mesh base that allows liquid to drain into a chamber below, which can be tapped off. Openings have been added to the side of the wheelie bin to allow the removal of castings from the lower part of the bin as they move down from the active feeding layer at the top of the bin. In addition, this worm farm has three special features:
As part of an initiative by Melbourne Council, restaurants have been encouraged to install above-ground worm farms, such as the hungry bin system.
The unit has wheels, so it is easily moveable.
It can be retrofitted to wheelie bins of various sizes, depending on the amount of waste you are likely to generate.
It is a continuous-flow system that does not require you to move and empty heavy trays of worm castings.
Homemade above-ground worm farms
For a more cost-effective worm farm, why not create your own? Using an old bathtub is one of the best options in our experience, but other large containers will also work. Mount your bathtub worm farm so that it is easy to drain the liquid fertiliser it produces. Food is continually added to the top of the system until the bathtub is full, a process that will generally take a year or more. You can extract castings by digging down into the bathtub, and a very useful strategy is to dig out one end at a time. Carefully sort the castings from the worms, which are returned to the bathtub. As you fill the empty side with food, the worms will migrate from the other side into the food – this makes it easier to then harvest the castings from the remaining half.
Smaller-scale above-ground worm farms can be created from second-hand containers such as polystyrene boxes. Worms are not particularly houseproud, as long as you keep bringing them food and regulating temperature and moisture conditions. You can either create a drainage hole at one end of the box to collect the liquid from your worm farm, or you can make multiple holes in the bottom of the box – as you would for a plant pot – and sit the worm farm under a lemon tree or the like, where the liquid fertiliser can drain into the soil and feed the plants around it.
It is also very feasible to build your own large-scale above-ground worm farm. Timber planks, rainwater tanks, water troughs and a variety of other large farm vessels can all be adapted to worm farming, and it is well worth consulting some of the excellent books available on the su
bject (see the Bibliography).
Collecting liquid fertiliser
Regardless of the type of above-ground worm farm you choose, the greatest benefit will be your ability to easily harvest the liquid fertiliser from it, in contrast to the in-ground worm farm that we will talk about next. All worm farms generate a certain amount of liquid, and the quantity depends on the moisture content of the feedstock as well as the amount of moisture that might find its way into the worm farm from rainfall or by deliberate application. If you are pouring additional water through the system to generate liquid fertiliser, it is important to ensure there is good drainage and high porosity, and to supply a refuge for the worms.
Generally, if no extra moisture is added to the system, a relatively small amount of very concentrated liquid is produced that is about the consistency of strong black coffee – this liquid is usually too high in nutrients to be used undiluted in the garden. Add water until it is about the consistency of weak tea (in other words, you are able to see through it), and you can be sure that the liquid will not burn your plants. This is especially vital for seedlings and new transplants.
Large-scale above-ground worm farms represent a viable and sustainable option for generating high-quality liquid organic fertiliser on urban farms of a more commercial scale, including peri-urban farms located on the edge of cities such as market gardens and cut-flower farms. If you are generating liquid fertiliser from an industrial-scale above-ground worm farm, then a more scientific approach to ensuring the optimum nutrient levels is worthwhile.
Top To Bottom: You can deliberately add an excessive amount of water to your worm farm to create an excellent all-purpose liquid feed. Simply collect the concentrated leachate from the drainage pipe, dilute it with water, and then use it on your plants.
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