There are clear rules for establishing and managing a good worm bed, but there is a lot of flexibility in applying these rules. The first requisite is that the bed be drained well. If the bed is open to the rain and it does not drain well, there is the risk that the worms will drown or will leave after a sustained heavy downpour.
Next, your worms will like some winter warmth and summer cool. You can achieve this if your bed is placed directly on the ground or is more than 300 mm deep preferably both. Your worms will then be able to burrow down to escape the extremes of summer and winter weather. Shallow beds, i.e. less than 300 mm deep, can be shielded from hot summer sun with shade cloth. At a depth of 450 to 600 mm, soil temperature in the temperate zones hardly varies all the year round from 15°C to 18°C.
However, don’t actually dig a pit for a worm bed. My measurements refer only to above-ground depth. A pit would provide good protection from extremes of weather, but it is dangerous. If your beds are in-ground and subjected to such prolonged and heavy rain that the surrounding soil becomes saturated, your pit would also_ Where then can the worms go to escape drowning? If the beds are above ground, while they may
still become wet they can always drain.
The simplest and least costly beds are just a mound on the ground, but they tend to become untidy with poor edge definition and suffer from an unnecessarily high rate of evaporation.
It is better to fit your beds with sides, starting at a height of 150 mm but making the frame in such a way that you can gradually build up to as high as 600 mm by adding sideboards as necessary. You can go higher, perhaps as high as 900 mm, but very deep beds tend to become difficult to care for and the lower levels may become compacted. In any event, there is no benefit or to operate very deep beds. Allow them to go to a height convenient for you to work at.
In constructing the bed, remember that you will want to remove the castings, preferably without the fuss and bother of first having to remove the worms. Construct it so that,-when you reach a height of around 600 mm, you can remove the boards at the base. This will enable you to scrape out the castings at the bottom without disturbing the top or removing the worms.
A good practical size for a worm bed is 2400 minx x 900 mm (8 feet x 3 feet’ and, for a start, 150 mm (6 inches) deep. Timber makes the best sides and any will do, though I think hardwood is best. Treated pine is suitable and the manufacturers of this timber assure me that the cocktail of chemicals used to treat the timber is permanently bonded and will riot affect the worms. (I have used treated pine and found this to be true.) A worm bed of this size and design. is big enough to supply castings for your personal use and is convenient to work with It is not too far to lean across if necessary, so the risk of back strain is minimised. You can keep very close to 100,000 worms in a fully-populated bed of this size, so that it becomes quite a simple matter to calculate the number of worms you have.
Above all, don’t use old wash tubs or corrugated iron for worm beds as the zinc coating will, be deposited in your castings in levels as high as 4000 ppm and, as a result, they will be useless.
A major drawback to laying your beds directly on the ground is that if trees are growing nearby, their roots can enter the bed and establish a thick fibrous mat. The tree will pump water from the bed as fast as you apply it and all this will go on without your knowledge so that, while you may think you are watering your worms well, the watering will in fact be totally inadequate. I have seen tree roots travel over 30 metres to get themselves into a worm bud. If there is a potential problem from nearby trees, you can avoid it by laying down weed mat or a sheet of builder’s polythene to cover the bed base. However, you should do this only if you are sure it is necessary. If it is, then the bed must either be on a slope, or you must shape a slope into the bottom by first laying sand under the polythene. Do not take the polythene lip the sides of the bed as this will form a swimming pool and worms do not like swimming. They will eventually leave or drown. If you were deliberately to maintain beds of this design, the feed on the bottom would quickly turn anaerobic, develop a Soul odour and either kill the worms or drive them out. (Such a system is recommended in one particular American book. It doesn’t work as a customer of mine has learned, to his great cost.)
An excellent bed for growing fishing worms is a lidless box elevated above the ground, or the type illustrated. When we use this method, we simply stand the bed on bricks, The drainage is efficient and, because the beds are off the ground and separated from each other, the fat worms cannot migrate.
If you aim to become a commercial producer of castings, then you will need to adopt a different design, incorporating much larger beds so arranged that you can access them with a front-end loader.