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.