Faced with continued store closures and shortages, and anxiety about going shopping, some people have been growing a sourdough starter in their kitchen. As a gardener, in the same spirit, I decided to start up a new redworm compost bin. I’m glad I did so, since the redworms are happily eating away at a portion of our household’s food scraps, though the process has also been a reminder of the patience required to depend on nature to do its work rather than being a consumer who can drive out and buy what you need after somebody else provided the patience. I will tell you how to create and tend your own bin to make worm casting compost, though you will have to provide the patience.
To start the bin, you will need: ½ to 1 pound of redworms (a special kind of earthworm, of the species Eisenia fetida), a container, a handful of soil, some bedding, water, and food scraps. The worms will eat the bedding along with the scraps, producing a batch of compost every 2-3 months. The redworm compost can be added to your soil or to potting mix where you plan to grow vegetables or flowers. It’s a good soil amendment and a high-quality fertilizer.
A worm bin can be kept indoors, with a drip pan beneath to catch extra liquid (which is also good fertilizer), or it can be put outdoors in a shady spot. If winter temperatures drop below 40, move the bin to a shed or garage, but in milder parts of the Bay Area it can stay outside all winter.
Start by learning if you have a friend with a worm compost bin who will share some worms with you when they next renew their bin. Redworms are also available from several online sources, which may also sell them as red wrigglers or composting worms, at a cost of $25-50 for a pound. (These are not, by the way, regular garden earthworms, but a smaller species that thrives in a compost bin, but would die out in garden soil.)
As a container, one can purchase complicated, several-tiered bins, but all you really need is a shallow (10 to 16-inch deep) box with a lid and a few drainage holes in the bottom. Because I was committed to using, as much as possible, what I already had, I repurposed a large plastic storage bin by drilling a few holes (only ¼ inch, so rodents can’t enter). If you have the wood and tools, you can make a wooden bin. One common plan requires a single 4 x 8 foot panel of ½ inch plywood, as shown on this information sheet from Washington State University: http://whatcom.wsu.edu/ag/compost/wormbins.htm. Or you can make a smaller one from a half sheet of plywood using this plan from the Alameda county StopWaste web site: http://www.stopwaste.org/at-home/home-gardening/all-about-compost/backyard-composting/build-or-buy-a-compost-bin/two-person. In either case, a prop stick is handy to keep the box open while you work in it. A wooden box keeps best if you can paint it inside and out with food grade mineral oil, but this step can be skipped or postponed.
Next, add bedding. Good options include newspapers or brown cardboard torn or cut into strips, dry leaves, hardwood sawdust, or straw (but not glossy paper). Fill the bin about ¾ full of bedding, then moisten it to wet but not dripping, using a spray bottle or sprinkling can and fluffing it to moisten throughout. Mix in a handful of soil, which the worms use in their gullets.
Tuck the worms under the bedding surface and add just a few kitchen scraps. Eventually the worms can process about a pound of scraps a week for each square foot of surface area, but they can only eat a little for the first few weeks, so don’t overfeed them. They can eat vegetable and fruit trimmings and peels, crushed eggshells, tea bags (minus the staple), coffee grounds, and small amounts of rice or torn up bread. Avoid oily foods, meats, or dairy products. Cover the bedding surface with a piece of plastic sheeting to keep in moisture and reduce the chance of fruit fly infestations. Remoisten lightly if the top of the bedding is dry—check especially in warm weather.
When you see the process is near completion, move the contents to one half of the box and add fresh, moist bedding to the other half. Put new kitchen scraps only in the fresh bedding. Most of the redworms will migrate to it in a few weeks, and then you can harvest the finished compost. (If you put little piles of it in bright light, any remaining redworms will hide in the centers of the piles, where you can find them and move them to the fresh bedding.)