What could be better than compost? Vermicompost! That is, compost made by worms. If you have little space for a compost pile or don’t want to spend money on a tumbler, you can easily build a bin for composting — all year round — that fits nicely in a closet or basement. And the smell of rotting organic matter? If you take a little time to manage the system right, it’s odorless.
To make worm compost, your worms need a place to live and do their work — somewhere damp, dark and not too cold. Dozens of commercial and do-it-yourself options are available. But here’s a simple, inexpensive method. Start with two 18-gallon plastic totes. Drill multiple 3/8-inch holes in the sides of one tote. These holes should be near the top of the tote sides, 4 to 6 inches from the top to allow air to flow through the bin so that the worms’ environment doesn’t become too humid.
Drill several 1/8-inch holes in the bottom of the same tote to allow excess water to drain out. Some worm wranglers choose to use only one tote without holes in the bottom, but this requires more careful management of the system. Usually, nothing should leak out these holes.
Before placing the tote with holes in the other tote, place some spacers in the bottom tote so the two totes don’t fit together tightly. These spacers may be short 2-by-4's or several small, repurposed plastic containers. After you’ve put the tote with holes on top of the spacers in the other tote, you’re ready to fill your worm bin.
Fill the Worm Bin
Worms cannot live by vegetable trimmings alone — they need bedding to create the best environment for them. Shredded newspapers, torn-up corrugated cardboard and leaves make wonderful bedding. Black-and-white newspaper pages on dull paper work better than the shiny pages with color. Corrugated cardboard offers ready-made tunnels for the worms, and it holds moisture well. Dip shredded bedding in water and wring out excess moisture. Sprinkle a handful of dirt in the bedding to provide grit for the worms’ digestive systems.
Compost worms do best in moderate temperatures — about 55 to 75 degrees Fahrenheit. They can tolerate slightly cooler temperatures, but a frost will kill them. They also continue to feed and reproduce at warmer temperatures (slightly above 80 degrees), but they may be harmed or die at temperatures above 85 degrees. Depending on your environment, you can move the bins to a shady spot outside during part of the year.
You’ve created a perfect habitat for compost worms (Eisenia fetida), not just any worms. Earthworms dug up from your garden or night crawlers from the lawn simply won’t create compost in this type of system. Red wigglers are the best type of worms for composting. They’re also called manure worms and quickly turn rotting organic matter into compost.
A pound of worms (about 1,000 mature worms) or more will live comfortably in an 18-gallon tote with 8 inches or more of bedding and vegetable scraps, but you can start with fewer worms and they’ll multiply — just feed them less. If the environment is right, you can plan on the worm population doubling about every 6 months.
Feeding the Worms
Worms love mushy foods, such as banana peels and cooked pumpkin. You can soften vegetable scraps by freezing and thawing them or chopping them in a food processor. The worms will eat larger, coarser scraps, such as lettuce leaves or broccoli stems, but the process takes much longer. In addition to vegetable and fruit scraps, you can feed some coffee grounds, tea leaves and crushed egg shells. Avoid feeding the worms things that you wouldn’t put in a compost pile — meat, dairy products, salt and oils. The worms will slowly process citrus peels and trimmings from onions and related plants, but it’s best to feed small quantities of these things and only occasionally.
Start slowly, feeding the worms a cup or two of trimmings each day or every other day. Increase the amount until the worms can’t eat the food in a few days. One common rule is that worms can process up to half their weight in compost each day when they’re acclimated and comfortable.
Put food in the bin several days before you add the worms. This allows the food to begin decomposing. Worms don’t really eat the vegetable and fruit trimmings you feed them; they eat the fungi and bacteria that grow as rotten food.
Worms eat the bedding as well as the food, so you’ll need to add bedding, too. In most cases, dampening the bedding before adding it to the bin is best. But if your system is too wet, some dry bedding can absorb extra moisture and help rebalance the humidity. If the system is too dry, dampen several sheets of newspaper or a single sheet of cardboard and lay it over the top of the bedding to keep it damp.
Harvesting & Using the Compost
Compost worms hate a few things: light, vibration and water (standing water, not dampness). If the bin becomes wet, the worms will climb up the sides. They’ll also start trying to escape if the bin is shaken, such as when it’s near a washing machine that causes the floor to vibrate. Light drives the worms down, and you can use this to harvest compost.
When a batch of compost is nearly complete, stop feeding the worms until they’ve eaten almost everything in the bin. Then, dump the compost and worms in a heap and put a light over it. After allowing the worms a few minutes to start moving downward, start scraping off the compost. As the worms are exposed to the light, they keep crawling down until you’ve scraped all the compost off the pile and only worms remain. Refill the bin with fresh bedding, half the worms (assuming they’ve had time to double their population) and some food.
With the other half of the worms, you can start a second bin, go fishing or feed the chickens. You can also sell them or give them away, of course. Online worm sellers charge about $30 per pound.
The composition of worm compost can vary by what you feed the worms. Joan Nusbaum, master gardener and vermicompost hobbyist from Colorado, fed her worms only bananas from fall until spring one year. She then had the compost tested at the Colorado State University soils lab and the results were as she expected — the potassium content was very high. Nusbaum says, “While the worms are not extremely picky about what they eat, offering a variety of foods will result in more balanced nutrients for your plants.”
Vermicompost can be higher in nitrogen, phosphorus and potassium than typical garden compost. But it usually contains more salts, too, so it’s best not to use too much at one time.
Avoiding (Or Solving) Problems
Fruit flies are probably the most common problem with worm compost bins — not for the worms, but for humans. The flies seem to be especially prevalent in the summer if you keep the bin outdoors, but are more annoying when the bin is inside your house. To avoid developing an infestation, don’t overfeed and keep fruit trimmings well buried under bedding.
If you develop a fruit-fly problem in spite of your best efforts, stop feeding the worms for 2 to 3 weeks and fill the bin to the top with bedding. During the weeks you’re not feeding, the bedding will settle, but you don’t need to add more to keep the bin filled. The bedding creates a barrier to keep the flies from the rotting fruit where they lay their eggs.
If the bin starts to smell like manure, it’s too wet. Add more bedding and reduce the amount you’re feeding. The vegetable and fruit trimmings you feed the worms add significant moisture to the environment. In some cases, a white mold may develop on the top of the bedding. You can remove this or turn it into the bedding. It doesn’t really hurt the worms.
Make it Yourself
(Corresponding pictures in slideshow at the top of the page)
Step 1: Build a simple worm bin with two 18-gallon plastic totes. Drill multiple 3/8 inch holes in the sides of one tote, near the top, to allow air to flow through the bin so that the worms’ environment doesn’t become too humid.
Step 2: Worms need bedding to create the best environment for them. Shredded newspapers, torn-up corrugated cardboard and leaves make wonderful bedding.
Step 3: Worms eat the bedding as well as the food, so you’ll need to add bedding, too. In most cases, dampening the bedding before adding it to the bin is best.
Step 4: Worms hate water, so if the bin becomes wet, the worms will climb up the sides. They’ll also start trying to escape if the bin is shaken, such as when it’s near a washing machine that causes the floor to vibrate.
Step 5: Light drives worms down, so use this principle when harvesting the compost: Dump the compost and worms in a heap and put a light over it. Allow the worms a few minutes to start moving downward; then start scraping off the compost.
Tea made from vermicompost can be used as liquid fertilizer. Some gardeners use the tea as a foliar spray to give plants an extra boost or to fight fungal diseases — though this isn’t scientifically proven. Use caution if spraying compost tea on food crops. The tea may contain microbes that cause illness if ingested.
Leachate, the liquid that may leak out the bottom of your worm bin, is not that same as compost tea. It’s closer to manure tea. The microbes are different and may harm plants.
Dozens of recipes for compost tea exist, but most suggest aerating the tea as you brew it to maintain and grow the aerobic microbes. As you brew the tea, it shouldn’t smell like manure (anaerobic). Here’s a basic method:
Start with well water or, if your water is chlorinated, allow the chlorine to evaporate for a day or two before starting the tea. Start your aerator. An aquarium pump usually works fine. Add a cup to several cups of vermicompost, either in a bag of loosely woven cloth (cheesecloth) or without a bag. You can also add a tablespoon or so of a simple sugar source, such as molasses, to increase the number of microbes in the tea. Be aware that if pathogens exist in the compost, sugar will also increase their growth. Let this brew for 24 to 48 hours, then strain. Some people add kelp, alfalfa pellets or other ingredients to give the tea an extra boost of minerals or nitrogen.
Use the tea immediately after brewing. If you wait, the aerobic microbes will start suffocating.
Troy Griepentrog has gardened in North Dakota, Minnesota, Kansas, and Colorado. Each of his gardens has included some sort of experiment.