Many gardeners are curious about vermicomposting but are unsure about how to start. To explain what you need to know to make a simple worm bin, my returning guest this week is Rhonda Sherman, one of the foremost experts on vermicomposting and the author of “The Worm Farmer’s Handbook.”
Rhonda is an extension specialist and the director of the Compost Learning Lab at North Carolina State University in Raleigh. She organizes the annual NC State Vermiculture Conference, which draws participants from around the globe, and travels the country and farther afield to present workshops on vermicomposting and consult with farmers, businesses and institutions.
If you missed last week’s episode, you will benefit from going back and listening to it before diving into this episode. Last week, Rhonda explained the benefits of vermicompost, including why it makes such a valuable soil amendment. This week, Rhonda will share the key facts to know and the steps to get started vermicomposting.
The Four Biggest Missteps of Home Vermicomposters
Overfeeding — Your worms won’t stick to a feeding schedule. You have to watch how much they are consuming and dial it back if their activity has slowed down. Ideally, you won’t give them more food until they have consumed what you gave them to eat at the prior feeding. If you keep adding more food, the worms will seek out the freshest inputs before consuming the oldest inputs, and those inputs will rot anaerobically.
Rhonda recommends having a backyard composting bin in addition to a worm bin so they have someplace else to put fruit and vegetable scraps.
Too much moisture in the bin — A worm bin should never be watered. This can create anaerobic conditions, which will really stink up the bin. The trick is to moisten the bedding before it goes into the bin, rather than adding water to the bin itself.
Failing to recognize you’re practicing earthworm husbandry — It’s so important to care for these animals and think of them as animals that you have to keep alive and thriving. You have to have the right conditions for them.
Failing to understand you need the proper species of earthworm — Most people think all worms are alike, and they’re not. The earthworms used in vermicomposting systems are epigeic, meaning they live in composting organic materials — not soil.
Making a Vermicomposting Bin
There are plenty of vermicomposting systems and products available for purchase, but Rhonda recommends new vermicomposters make their own. It’s unnecessary to spend hundreds of dollars on a worm bin, she says, when it’s easy to make one out of an opaque plastic tote.
A 14-gallon plastic tote with holes drilled into it (in specific places) is all that’s necessary to get started, and it costs less than $10. Many home vermicomposters keep their worm bins in their basement, but Rhonda has known people who keep theirs in their master bedrooms closet or who have a lovely coffee table that doubles as a worm bin.
First, make plenty of holes in the top inch of the sides of the bin, using the smallest drill bit you have. And never put holes in the lid, because keeping light out and moisture in is important. The worms need 80% moisture, especially in the top four inches of the bedding inside the bin. Rhonda says some worm bin manufacturers must not understand the needs of worms because they put holes in the lid for air, but keeping the moisture in is the most important thing to do. Those holes on the sides of the bin, nearest the top, will suffice to provide oxygen.
You will also need about six quarter-inch holes in the bottom of the bin so excess liquid can drain out. The bin should sit on a tray or an extra lid to catch all of the liquid, though Rhonda notes that if the moisture in the bin is managed correctly, there won’t be any excess liquid.
Leachate Vs. Worm Tea
Rhonda calls excess liquid from worm bins “stinky, mystery liquid.” It’s leachate, and it’s stinky because it’s anaerobic, meaning it contains microbes that proliferated in the absence of air. It is NOT the same as worm tea, which is beneficial for plants. This stinky leachate could contain salts, acids and pathogens that are bad for your plants.
When I was new to vermicomposting, I saved some leachate and diluted it 10:1 with water. I poured that mixture into the pots of some azalea plants I was growing that were struggling. By the next day, I noticed an improvement.
Rhonda says there are vermicomposters who likewise have success using leachate on their plants so they purposely add excess water to their worm bins to get more of it. This is bad for the worms and the environmental conditions they require to thrive, and it is also risky for your plants. She says if that worm bin contained spinach contaminated with E. coli, for example, that leachate applied to your garden will contain E. coli.
Actual worm tea is an extract of worm castings, made in a brewing system.
The Right Temperature for Worm Bins
The earthworm species that Rhonda recommends for worm bins do best in temperatures between 60 and 80 degrees. They will consume the most food, produce the most babies and make the most castings in this range. They can tolerate temperatures in a wider range but their activity will slow down.
Humidity plays a part as well. In California, where there is low humidity, the worms may really like 95-degree weather. But where Rhonda is in North Carolina, there is high humidity, and 95 degrees is too hot for her worms. So be conscious that your local conditions must be taken into account.
Rhonda’s worms live in an unheated and uncooled worm barn on a university property. Her worms have survived when the heat has reached 100 degrees and also made it through three days of 10-degree weather, even after the top three inches of the worm bin formed ice. In fact, ice is a good insulator, so commercial vermicomposters who expect freezing temperatures will mist the tops of their bins to form that ice layer.
With proper insulation, worms can survive outdoors in the wintertime in a region as cool as New England, Rhonda says. And even if the adults die, worm cocoons persist through the winter and hatch once conditions are right.
Citrus in Worm Bins
Citrus fruits — lemons, lines, oranges, clementines, grapefruit, citron, kumquat and more — contain citric acid, which is a problem for worm bins when there is too much of it.
If you have a small worm bin, you never want to add citrus, so just toss it in your regular compost instead. If you have a very large worm bin, like Rhonda’s four-foot-by-eight-foot bin, some citrus won’t be an issue. “But if you have a small 14-gallon bin, the citrus just overwhelms the system,” she says. “It adds too much acidity, it throws the pH off balance, and it could really muck up your system.”
Do Both, Not One or the Other
Compost improves tilth and porosity of soil, adds nutrients and increases microbial activity among many other benefits. Vermicast complements regular compost and supercharges it. Vermicast is like salt added to your favorite dish. It’s the enhancer that makes it better, though a little goes a long way.
Choosing and Wetting Bedding Material
To maintain the property moisture level in a worm bin, it’s important to include stable organic material. This is the bedding that the worms live in. Shredded newspaper, office paper or cardboard are all popular bedding options. Leaves can work, but they tend to carry fly eggs that will hatch, which will certainly be a problem if your worm bin is kept indoors.
Keep in mind that soil is not appropriate bedding material for a worm bin. The worm species that are appropriate for worm bins don’t live in soil in the wild — they live in decaying organic material.
An easy way to get started is to fill the 14-gallon bin halfway with wet shredded paper. Rhonda says to start by soaking the paper in a bucket of water for 10 minutes before adding it to the bin so it gets wet all the way through — not just on the surface. Pull the paper apart, then place it in the bin.
You should never add water to your worm bin. You should only add wet bedding material.
It is important to remember that peat is naturally acidic, so lime must be added to adjust the pH. Peat is popular bedding for commercial worm growers — businesses that are raising worms for sale rather than producing vermicast for sale. Peat moss is falling out of favor with many gardeners because harvesting peat is not a sustainable practice and it creates carbon emissions.
Coir is a byproduct of coconut farming, and it’s imported to the United States, so coir too has a carbon footprint. It just makes more sense to use free materials that you already have around, such as used paper.
For more experienced vermicomposters working on a larger scale, finished compost and aged composted manure make good bedding. They must be aged because immature compost or uncomposted manure will heat up as it decomposes, and that would be bad news for the worms.
The Best Worms for Vermicomposting Bins
Out of 9,000 species of earthworms, scientists have determined that just seven are suitable for vermicomposting. In the United States and around the world, the preferred earthworm is Eisenia fetida, commonly known by the names red wiggler, tiger worm, redworm and manure worm.
Eisenia fetida eat a good amount and reproduce well, Rhonda says, and they have a better temperament for vermicomposting. “You’re putting them in a confined space, and you want them to stay there,” she says, “and so it’s really important to get just Eisenia fetida. Try not to have other species mixed in because they probably won’t get along.”
Some species of earthworms are “flighty,” and will find their way out of confinement. “It’s like the grass is greener,” Rhonda says. “They want to leave that bin and go somewhere else.”
How Many Worms to Start With
To set up a worm bin, start with no less than a pound of red wigglers, Rhonda advises. “Don’t cut corners and get less than that,” she says. If you start with fewer worms, you will be more likely to overfeed them.
One pound of red wigglers is about 1,000 worms. Buy them from a professional worm grower instead of trying to find them yourself. If you just grab the worms you find on your driveway after a rain, you’ll end up with a variety of species, none of which are likely to be red wigglers. It’s important that you know what you are getting and what’s going into your worm bin.
Rhonda also advises against getting worms from a bait shop. You may pay $150 for a pound of red wigglers at a bait shop rather than around $50 from a worm grower.
Worms from a worm grower will come in a bag or a box. Gently empty the worms into a worm bin half full of moist bedding. You can then leave the bag on top of the bedding and come back the next day; the worms will leave the dry bag for the moist bedding. If you try to pull the worms off the bag yourself, you may end up squishing them because they are very fragile.
When the worms arrive, they won’t be hungry immediately. They need time to get acclimated to their new bedding after experiencing disturbing vibrations while they were shipped on a plane and truck.
To ensure the worms don’t try to get out of the bin because they are still “freaked out” by their journey, Rhonda says, keep the bin in a lit room for a few days until they settle down. They will stop trying to get out and will stay in the dark bin because they hate light.
Keep a three-pronged garden tool on hand to pull back some bedding and create a hole, put the worms’ food in it, and cover up the food with bedding. Rhonda says if you don’t cover the food you will regret it because you will get fruit flies.
What to Feed Vermicomposting Worms
Just like with a regular compost bin, don’t put meat, fat, grease, bones, fish and dairy products into a worm bin. They can attract carnivorous animals and really stink while they decompose. Not to mention the pathogens those ingredients may carry.
Vermicomposting worms like a variety of fruit and vegetable scraps, and also coffee grounds. Adding nothing but banana peels or nothing but coffee grounds won’t work. Though coffee grounds are a favorite of vermicomposting worms, too much will make the worm bin too acidic and too wet.
You don’t need to get hung up on providing a balanced meal to your worms, but you want a nice variety, Rhonda says.
The worms may beeline to certain types of food and ignore other types of food. For example, they love melons (just water and sugar) and lettuce (which breaks down easily) but hard broccoli stalks (which even humans struggle to chew up) will sit in the bin for a long time.
Chopping the inputs into small pieces will create more surface area, making it easier for the worms to consume them.
The worms will eat the paper and cardboard bedding as well, so you can go on vacation and not have to worry about hiring a worm-sitter to feed them. Black ink and colored ink on modern newsprint and cardboard are vegetable based and safe for worms, but avoid glossy paper, which contains clay or a polymer to give it its sheen.
Monitoring a Worm Bin
Check your worm bin every day — if you can — to identify and address any issues before they get out of control.
The first thing to look for when opening a bin is worms, though you actually don’t want to see any. If the worms are wriggling down deep in their bedding, those are happy worms. And a few worms on top of the bedding that dive down once exposed to light are no concern either. But worms that are on the sides or the lid are of the bin are a sign of a problem.
Rhonda says to count up the worms on the lid and sides, and if there are fewer then six, things are going fine. But if it’s more than six worms, it could mean the bin is too wet, too dry or the wrong temperature. It could also be the case that the worms were overfed and now the rotting food is releasing gas that makes the bin an inhospitable environment.
A ball of worms above the bedding is a sure sign that there is a problem, according to Rhonda. To troubleshoot, check out Rhonda’s paper “Worms Can Recycle Your Garbage.” It identifies common problems and the solutions.
Worm bins rarely get moldy, but it can happen, especially if old moldy bread or another moldy input was added to the bin. Rhonda recommends running the moldy bread through water from the kitchen faucet — don’t soak it — and then put it into the worm bin. This should prevent a mold issue in the in.
If you have an intense mold allergy, be careful not to ever add moldy foods to the worm bin. A moldy bin will release mold spores into the air when opened.
How to Harvest Castings from a Worm Bin
In a single-bin vermicomposting system, the castings accumulate at the bottom of the bin. The castings appear soil-like, and they don’t smell. Once there are several inches of castings in the bin — this can take four to six months from when you got started — it’s time to harvest.
What you don’t want to do is turn or stir up the contents of the bin. You want to maintain separate layers, with the castings on the bottom and the bedding on top.
If you have a multi-tray worm bin system, the castings will accumulate in a separate tray.
Light separation is a harvesting method that’s based on earthworms’ aversion to light. Put down a plastic tarp or old shower curtain outdoors on a sunny day or indoors under a bright light, and dump the bin’s contents on it. The castings will now be at the top of the pile, and the bedding will be at the bottom. The worms will head for the bottom and into the bedding, away from the light. Put the castings in a separate container, and fill the worm bin halfway with moistened bedding material. Then return the old bedding and any stray worms to the bin.
Horizontal harvesting doesn’t require handling worms. It works by visually dividing the bin in half vertically, and only adding food to one side of the bin for at least three weeks. The worms will gradually migrate to that side, attracted to the fresh food. When you notice that most of the worms are absent from the side that hasn’t been fed, you can harvest the vermicast underneath the bedding on that side. Once the vermicast is harvested from one side, reverse the process. Fill up the side where the worms were absent with new moist bedding, and begin adding food to that side only.
Vertical harvesting is for worm bins with multiple stacked trays. It starts by adding worms and food in the bottom tray with bedding. When the vermicast builds up there, add a tray to the top with bedding and only feed in that tray. The worms will migrate to the upper tray where the food is. Once the worms have migrated out of the bottom bin, the castings can be harvested and that bin can be moved to the top.
How Worm Bins Maintain Populations
In a successful worm bin, the worms will maintain and even grow their population. If you have excess worms, you can start a new worm bin or give them to someone else who wants to start a bin. But don’t add the worms to your garden or lawn because they don’t live in soil and won’t survive.
Vermicomposting worms living in a confined space, particularly in larger worm bin systems, will adjust their population to its space rather than over-reproduce. So having an excess of worms is rarely an issue.
I hope you enjoyed my conversation with Rhonda Sherman. If you haven’t listened yet, you can do so now by scrolling to the top of the page and clicking the Play icon in the green bar under the page title.
Do you practice vermicomposting? Let us know in the comments below.
Links & Resources
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“Vermiculture Technology: Earthworms, Organic Wastes, and Environmental Management” edited by Clive A. Edwards, Norman Q. Arancon and Rhonda Sherman
“Tea Time in the Tropics” by Norman Arancon and Theodore Radovich (free PDF)
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