Organic gardeners are well aware of the role worms play in healthy soil. In fact their presence or lack there of is a tell tale sign of whether soil is healthy or not. Vermicomposting is the process of using worms to digest organic matter in specially constructed worm bins, where it is processed into a nutrient-rich organic fertilizer and soil conditioner commonly referred to as worm casings, or worm manure. Vermicompost improves soil by improving its physical structure; enriching soil in micro-organisms; adding beneficial plant hormones and enzymes; attracting deep-burrowing earthworms already present in the soil; improving water holding capacity; enhancing germination, plant growth, and crop yield; and improving root growth and structure.
Any worms can be used for this process, but all worms are not created equal. The earthworm species known as red wigglers have been found to be the most efficient for vermicomposting. Each red wiggler can process the equivalent of their body weight daily. Generally it is best to start your worm box by buying a good quantity of red wigglers which are available from many online sources.
Most home vermicomposters construct or buy small-scale systems. Plastic bins have few drawbacks and are readily available, but bins should not be constructed of Styrofoam or metal as these may release toxins or conduct too much heat. If constructing your own container, wood has the advantage of better breathability and lower heat conduction. There are two main types of bins that can be constructed or purchased. Non-continuous bins consist of a single box with small air holes in the sides, a top to shut out light and sometimes a drain tray to collect extra moisture. With a wood bin you may be able to get away without a drainage tray because wood breaths and absorbs excess moisture and condensation does not form as readily on wood as it does on plastic. Continuous bins have more than one chamber stacked either vertically or horizontally. Bins can be separated by a wire screen with holes large enough for worms to migrate from one bin to another.
One advantage continuous bins have is that once the first bin becomes full, bedding and food are added to the second bed and as remaining food is depleted in the first bin the worms will migrate to the second bin in search of food. Opening the lid on the first bin will encourage the worms to migrate in search of darker quarters. Once all the organic matter has been consumed and worms have migrated to the second box you will be left with rich castings to use as compost in the garden. With non-continuous bins harvesting castings is a little more difficult. Once the bin becomes full and organic matter is depleted, the contents can be removed to a sheet of plastic or tarp that will allow it to be spread in a thick layer. The worms will move to the bottom of the castings, moving away from bright light. Do not do this in direct sun or allow the worms to dry out. It will be difficult to separate all of the worms from the castings you remove, but the ones that go with the castings will continue to do good work in the garden. The remaining worms and a small amount of castings will be placed back in the bin on bedding and the process will begin again.
For starting the vermicomposting bin, moist bedding is put into the bin and the worms are added. A handful of food is added and covered with an inch or two of bedding, and new food is not added until most of the previous food has been processed by the worms. Rotate around the corner each time food is added and only add a handful of food at a time. Bedding provides living quarters for the worms and also an additional food source. Bedding can consist of shredded newspaper, sawdust, peat moss, hay, aged manure, dried leaves or a combination of these or other appropriate medium.
Worms used in composting systems prefer temperatures of 55 to 70 degrees Fahrenheit. The temperature of the bedding should not drop below freezing or rise above 89.6 °F. Worm bins that are properly maintained do not smell bad, so it is possible to move them inside the garage, greenhouse or house when needed to maintain proper temperature.
When composting, we are used to maintaining a ratio of brown matter rich in carbon and green matter rich in nitrogen. There is also a ratio preferred by worms and other composting organisms. The material used as bedding consisting of brown matter should make up most of the bin contents. One part green matter (food) should be added to 30 parts bedding.
Suitable food sources for your worms and microorganisms include the following: many kitchen wastes and leftovers; plate scrapings that do not contain meat, rotting fruit or lettuce, moldy bread, and coffee grounds. Green leaves from garden plants are also suitable, but thick stems should not be included. Avoid the following are foods: Citrus peels, banana peals or melon rinds, grass clippings unless you know they have not been sprayed with pesticides, meat, high fat items, bone, high salt foods and spicy foods including onions and garlic. It is best to freeze and thaw raw vegetable or fruit and their peelings before adding to the bin. This kills undesirable fly eggs that will hatch if placed in the bin.
Nick Fraser is a free-lance writer.