What does home vermicomposting involve? Acme Worm Farm’s wormkeeper, Tom French provides some answers. Click here to send us your home vermicomposting questions. Be sure you also read our article on Commercial Vermiculture.
The Worm Bin
Your worms don’t need to be in a box, but it makes it easier to keep them in a herd. The best materials are wood or plastic. Metal gives off poisons as it reacts with the moisture and acids in the bedding. The bin should be at least eight inches deep, preferably 12-16 inches, and should be wider than it is deep. A good working size is two feet by three feet by one foot deep. Drain holes are needed in the bottom to insure that the bedding doesn’t become saturated with water. They also help increase airflow through the bedding. If you are using a plastic tub, drill a 1/4 inch hole every 3 inches both directions. You won’t need any screen to keep the worms in. If there is something wrong with the bedding, they will find another way out, or even crawl through the screen if they have to. Put something under each end or corner of the tub so air can get to the bottom. DO NOT USE THE PLASTIC LID. Cover the bedding with a piece of burlap or cardboard. If you use cardboard, cut it so there is a 1/2 inch space all the way around for air to enter. An even better option is to stretch a piece of burlap over a wood frame, and set it on top of the bin. You can go one step further, and keep the burlap moist by sprinkling water on it. The worms will like the humid atmosphere as they crawl around on top of their food at night.
Although plastic tubs will work, and are commonly used, worms like wood better. One advantage of wood is that it breathes. As moisture wicks through the wood, air is drawn into the bedding. Either drill a 1/4 inch hole every 3 inches both directions on the bottom, or drill a 1-inch hole for every square foot. If you go with 1-inch holes, staple a little piece of plastic window screen over each hole.
The bin pictured is made with 2×12″ sides and a 3/4″ plywood bottom. You can build the same bin for a fraction of the cost by using 1/2″ plywood for both the sides and bottom, and it will last for about three years. Half inch OSB is even cheaper, and works just as good. If you use plywood or OSB, you will need 2x2s or 2x4s to fasten the bottom to the sides. The strongest design would have the 2x2s fastened along the bottom of the sides under the plywood floor. 2x4s work good for the legs. Use screws designed to resist corrosion. All of these materials can be had for free from scrap piles at construction sites.
The Worm Bedding
It is extremely important to have some compost in the initial bedding. This cannot be stressed enough. Aged manure makes great compost. If you want, you can lighten it up a little by adding some peat moss or coconut fiber (up to half by volume). It’s a good idea to soak the peat moss or coconut fiber in an excess of water and then squeeze the water out to reduce the acidity. The bedding should be almost soggy. A few drops of water should come out of a handful when squeezed. If ordering worms through the mail, make sure the bin is ready before the worms arrive. There is no way of knowing how long they will live in their packaging after they arrive. It might be a few days or a few minutes. Start with about six inches of bedding. When the worms arrive, dump the worms, and the bedding they were packed in, in the center of the bin. After the worms crawl in, spread out the pile of bedding, and feed the little guys right away.
Feeding Your Worms
Ideally, kitchen scraps should be partially composted before going in the worm bin, but this is not always feasible, and not really necessary. Do not put any meat or dairy products in the bin. No hot spices, and absolutely no salt. Fruit and veggie scraps should be cut into 1/2 inch strips. This allows more aeration than dicing or blending. If you are using a large bin like the one below though, there is no need to cut up your worm food, or to mix with fiber. Mix the scraps you cut up with your other suitable worm food like coffee grounds and tea bags, and add about 30% shredded paper, or brown leaves, straw, gain chaff, hardwood shavings, ripped-up coffee filters and napkins, or some other high carbon material that will aid in aeration. Because the carbon will speed up decomposition, it could cause the bin to heat up if overfed.
Try to develop a feel for the right amount of fiber, and the right amount of food at the right time. Put an inch or two of this mixture on top of the bedding. Always wait to feed the worms until they have eaten a good portion of their last feeding. In the meantime, your excess veggie-fiber mixture can be allowed to age for a while, or put in the freezer. Freezing will break the cell walls, speeding up decomposition. Allow this mixture to reach room temperature before feeding to the worms unless the bedding happens to need cooling. Compost type earthworms need lots of calcium. Allow your eggshells to dry, then run them over with a rolling pin, and sprinkle on the worm food every time you feed the worms. If you don’t eat eggs, ground up oyster shells will work, and will also supply the needed trace elements. Taste the oyster shells to make sure they aren’t salty. A good supplement recipe is eggshells or agricultural lime or just oyster shells.
Compost worms are a low maintenance form of livestock. They don’t need to be milked twice a day, they are not susceptible to disease, and they won’t keep you awake at night. They do, however, need to be kept somewhat happy or they will crawl away while you’re sleeping.
The ideal temperature for Eisenia fetida is 72-75 degrees Fahrenheit. Reproduction and food consumption drop rapidly at temps below 60. They will survive the cold as long as they don’t freeze. If they do freeze though, most of the cocoons usually survive to hatch in the spring. They can survive temperatures up to 90 degrees for short periods of time, but it really stresses them. This of course is the bedding temperature, which is slow to change. Unless you have a small bin sitting in the sun, the temperature will be the same day and night. Decomposition of organic matter, and the activity of the worms, can help raise the bedding temperature during the winter. The flip side of this though, is that large worm beds can become warmer than the average air temperature in the summer. If you live in an area with very hot summers, you might need to keep the bin inside your house. Otherwise, you will need to use some tricks to keep the bin cool.
One way to help ease this situation is to feed the worms compost. It might also be necessary to ration their food. Keeping the bedding on the wet side will slow down the temperature rise from decomposition. Keeping the bin in a well ventilated area will help. Putting frozen food in the bin with the lid on will help. You can also put frozen water bottles in the bedding.
At ideal moisture, there will be very little or no liquid coming out the bottom of the bin. If excess liquid comes out, it won’t affect the worms that much, but can make the castings less valuable. It’s better for the worms for the bedding to be too wet than too dry, but over-wet conditions are more favorable to pests like flies and mites. Try to maintain the moisture at a level that leachate just barely wants to come out the bottom but doesn’t. It’s better to water more often, and less at a time. If you are feeding mostly high moisture foods like lettuce and melon, you might not need to water at all. Eisenia fetida can tolerate a wide range of moisture, and the only problems will usually be a decreased appetite in an overly dry bin. Use lukewarm water except when the bedding needs to be cooled. Do not use chlorinated water or water from a water softener. An inexpensive charcoal filter will remove chlorine.
When the bin is full, it is time to remove the worm castings. There will be castings throughout the bin, but the highest percentage will be on the bottom, and most of the worms will be near the top. If you take off the top four inches of bedding, you will have removed most of the worms, but it’s best to go down 6-8 inches if you want to recover most of the cocoons. A manure fork is best to remove the material off the top, but a garden fork will also work. Dig the worms out fast enough that they don’t crawl down before you’re done. The material you remove with the worms will fluff up to about 1-3/4 times the volume it was in the bin. Because the worm population will have at least doubled by the time the bin filled up, you can put the worms and bedding back in two bins the same size, or one larger bin, or give some to a friend.