Redworms need to breathe oxygen, but in deep containers bedding can
pack down and become airless, temporarily preventing the worms from
eating the bottom material. This might not be so serious because you
will stir up the box from time to time when adding new food. But
anaerobic decomposition smells bad. If aerobic conditions are
maintained, the odor from a worm box is very slight and not
particularly objectionable. I notice the box's odor only when I am
adding new garbage and get my nose up close while stirring the
material. A shallow box will be better aerated because it exposes
much more surface area. Worm bins should be from eight to twelve
inches deep.
I constructed my own box out of some old plywood. A top is not
needed because the worms will not crawl out. In fact, when worm
composting is done outdoors in shallow pits, few redworms exit the
bottom by entering the soil because there is little there for them
to eat. Because air flow is vital, numerous holes between 1/4 and
1/2 inch in diameter should be made in the bottom and the box must
then have small legs or cleats about 1/2 to 3/4 of an inch thick to
hold it up enough to let air flow beneath. Having a drip-catcher--a
large cookie tray works well--is essential. Worms can also be kept
in plastic containers (like dish pans) with holes punched in the
bottom. As this book is being written, one mail-order garden supply
company even sells a tidy-looking 19" by 24" by about 12" deep green
plastic vermicomposting bin with drip pan, lid, and an initial
supply of worms and bedding. If worm composting becomes more
popular, others will follow suit.
Unless you are very strong do not construct a box larger than 2 x 4
feet because they will need to be lifted from time to time. Wooden
boxes should last three or four years. If built of plywood, use an
exterior grade to prevent delamination. It is not advisable to make
containers from rot-resistant redwood or cedar because the natural
oils that prevent rotting also may be toxic to worms. Sealed with
polyurethane, epoxy, or other non-toxic waterproofing material, worm
boxes should last quite a bit longer.
How big a box or how many boxes do you need? Each cubic foot of worm
box can process about one pound of kitchen garbage each week.
Naturally, some weeks more garbage will go into the box than others.
The worms will adjust to such changes. You can estimate box size by
a weekly average amount of garbage over a three month time span. My
own home-garden-supplied kitchen feeds two "vegetableatarian"
adults. Being year-round gardeners, our kitchen discards a lot of
trimmings that would never leave a supermarket and we throw out as
"old," salad greens that are still fresher than most people buy in
the store. I'd say our 2-1/2 gallon compost bucket is dumped twice a
week in winter and three times in summer. From May through September
while the garden is "on," a single, 2 foot x 4 foot by 12 inch tall
(8 cubic foot) box is not enough for us.