The Basics of Worm Composting

What is worm composting?

Many people turn to worm composting (or vermicomposting) as a way to keep everyday kitchen waste out of the trash. Even if you don’t have a garden, composting is an admirable step toward a no-waste lifestyle, and using a worm composting system is one of the easiest ways to start. But for gardeners, worm “castings” (really just a nice word for worm poo) provide an amazing soil amendment for backyard plots.

How does worm composting work? There’s no polite way to put this: worms eat food material as it starts to decay, then excrete some of the most nutrient-rich, garden-ready compost you can get. You can keep a worm composting bin in your kitchen, pantry, garage, or even a classroom, as long as it’s a relatively controllable climate. The small size and self-contained design of a worm compost bin makes this system perfect for people who live in apartments or otherwise don’t have a lot of outdoor space.

While the prospect of starting a vermicompost operation in your home can feel complicated, we’ve laid out all the basics (and then some fun frills) to make this enviro-endeavor as simple as possible. The good news is that you’ve got your worm community started, they’re very low maintenance.

Getting Started with Worm Composting

Supplies for Worm Composting

You will need:

• Containers
• Worms
• Bedding material (“brown” compost ingredients)
• Food scraps (“green” compost ingredients)

There are two options for your worm compost container: building your own bin system or buying one.

Make Your Own Vermicompost Bin System

Creating your own worm composter is inexpensive but takes a bit of set-up effort. Use two or three shallow plastic bins or wooden boxes with removable lids. Make sure your containers are opaque; worms don’t like light and clear bins will lose temperature and moisture. 

You’ll be arranging a stack of at least two containers with a way for worms to travel between bins—simply drilling a grid of holes across the bottom of the bin for the worms to use as passageways will do the trick. You can also make the bin completely “bottomless” and place a mesh or wire screen at the bottom.

Drill a series of holes near the top of each bin as well, on the sides, for air flow. Place the seal-able top of the topmost container. (Don’t make any holes in the lids.)

Elevate your bin system off the ground with bricks—the moisture run-off from you compost will drain out the bottom bin, providing “compost tea,” nutrient-rich liquid that’s perfect for watering your garden. Place another bin’s lid underneath the entire stack as a “catch tray” for your compost tea.

Pre-made Vermicomposting Bins

Buying a snazzy pre-built container from a local store or online is super quick and easy, and often much more fashionable than a DIY worm bin system. The market is flush with brightly colored and easy-to-use designs to choose from (so you can match your compost bin to your kitchen aesthetics—fashion and function!).

One-Bin System

It’s possible to make a worm composting system with only one container, but things get significantly trickier when it’s time to harvest. “One-bin” explains it all: this method simply uses a single container, with layers of compost and bedding, as the worms’ environment. A plastic bucket with a lid will work just fine. 

Just be ready to sift through the finished compost to pick out worms!

Read on below to understand how to harvest your finished worm castings. 

Best Worms for Vermicomposting

You might be surprised to learn that “red wriggler” isn’t just a cute nickname for any worm, but a specific type of worm—the kind that you want for your compost system! When provided with the right food and living conditions, one pound of red wiggler worms can digest up 50–100% of their weight in kitchen scraps every single day.

Buy worms at a local gardening store, online, or even at a local bait shop (red wrigglers are typical fishing bait). Red wrigglers thrive in moderate climates, are happy living close together, and don’t burrow very deeply, so they are ideal for keeping in your indoor compost bin.

If you buy online (or at some stores), your worms will likely arrive in a protective cocoon that you can add directly to the compost bin. Eggs will hatch in one or two months and mature in about 10 weeks. Be sure to keep their bedding moist and warm while they hatch, and don’t feed them too much until you see them growing and wriggling. 

Within a few weeks of getting settled, the worms will mate, lay eggs, and begin to multiply. In fact, you’ll notice after a few months that you might have too many worms in your bin. Time to teach your neighbors how to set up a vermicompost bin… or go fishing!

Remember that worms are small, and while they can eat a lot, their mouths are tiny, so their bites are tiny, too. Be sure to crush up egg shells, tear up any brown waste (paper towels, etc.), and break down other large additions to the bin so that the worms can eat them before they start rotting.

Ideal Conditions for Worm Composting

Moisture and temperature will be your two biggest concerns for keeping happy worms.  

The compost should remain moist, about the feel of a damp (not soggy) sponge. If your compost is too dry, the worms will dehydrate. If it’s too wet, the ingredients could rot and smell. 

A room at 55º to 75º Fahrenheit is a worm’s happy place. Remember that your wrigglers will create their own heat as they eat and digest, so the compost bin will become warmer than the room temperature—and that’s good!

Setting Up a Worm Composter

Once you’ve decided which container type works best for your home, fill the bottom bin half-full with slightly moistened bedding material (“brown” compost materials like ripped up paper towels, black-and-white newspaper, etc). Sprinkle some coffee grounds or a little sand on top—the worms need “grit” to digest. Place the worms on top of all of this. Cover the bin and let it sit for a week before adding any kitchen scraps as the worms get comfortable.

In one week, add a few small handfuls of kitchen scraps (chopped into small chunks), then cover with a sprinkle of additional moist bedding material. Wait several days for the worms to start snacking—adding too much food right away is a sure-fire way to get a rotting, stinky bin. 

Place another bin on top of the foundation bin with the same bedding structure. Worms will crawl into the top-most bin, looking for new food.

Making Worm Compost 

Maintenance and Harvesting Worm Castings

Finished fluffy, nutrient-rich compost material will accumulate at the bottom of the bin as worms work their way upward to find more food. Remember, red wrigglers aren’t deep burrowers, so you should expect to find some near the top layer of your compost. If you don’t see them there, they’re still working through the bin underneath.

Harvesting your finished vermicompost is simple with a multi-bin system. Just remove the bottom bin from the stack, transferring the finished compost directly to your garden. The worms’ current home will now become the bottom of the stack. Place the newly emptied bin on the top of the stack and build fresh bedding as described above. You can do this with three bins or two.

Start adding scraps to the top bin, and soon your worms will wriggle their way up, leaving a new container of vermicompost material in the bottom bin. When you see the worms in the top bin, it’s time to rotate again.

There may be accumulation of compost tea run-off every few days, depending on what kind of food you put in your bin. You can water this healthy liquid right onto your houseplants or outdoor garden. Many store-bought bins have a spigot for gathering compost tea.

One-bin Casting Harvesting

One-bin harvesting is a bit more complicated—be ready to get your hands dirty. It’s often called “sifting” since you’ll be separating the finished compost from the in-progress stuff. 

To isolate the finished worm castings, feed your worms heavily on one side of the bin and wait a few days. The worms will congregate on one side so you can move the bedding from the opposite side to gathering the compost underneath.

There will likely still be a few worms and some un-eaten organic material mixed in with the finished castings. Use a sifting device like a colander, screen, or slotted spoon to sort the good stuff (which will be fluffy, dark brown-black, and nice-smelling) from the worms and leftover pieces of kitchen scraps. Throw the worms and remaining food pieces back into the bin.

Moisture in Vermicompost Bins

It’s essential to keep your vermicompost bin at the perfect moisture level. 

If the bin is too moist, you may see liquid buildup on the sides of the bin, or compost will appear muddy. A too-moist bin can also lead to rotting food and, as a result, unpleasant smells emanating from your compost. Not to mention it may drown your worms! 

To fix an overly moist bin:

• Add dry bedding material like shredded paper or cardboard at the corners.
• Move your bin to a sunnier spot.
• Move the more lush soil from the corners into the center of the bin.

If your bin is too dry, your worms could die. To fix a dry bin, you can:

• Add pureed veggies.
• Add more moisture-rich foods like cooked rice.
• Add moist bedding material to the middle of the bin.
• Spritz water on top.

Pro tip: Don’t use water treated with softener—the salt will kill the worms.

Temperature in Worm Compost Bins

There isn’t too much you can do about overheating except move your bin to a cool place, away from direct sunlight. This is usually only an issue in hot summer months. Think: a pantry, closet,  garage, or basement. A too-hot bin can start stinking!

If you live in a cold climate, winter time might make your bin too cold, especially if you don’t have central heating. Worms will get sluggish and stop eating if they get too chilly. See tips below in Troubleshooting for fixes for a cold climate. 

Worm Food

Like any compost pile, your vermicompost bin needs the right mix of “green” (nitrogen-rich) and “brown” (carbon-rich) materials. Worms also need “grit” to digest. 

The difference between outdoor-kept composters and your indoor worm bin is right under your nose. If it smells when you cut or cook it, it will make your worm bin smell. Save the super-stinky foods (onions, garlic, etc.) for your outdoor compost bin.

Many of your average kitchen scraps will make perfect green nitrogen materials, and you’ll sparsely add some brown materials like paper, fibers, and dry leaves for carbon. 

Here are our recommendations to concoct a delicious menu for your worms:

DO Feed your worms: 

• Food scraps (including roots, stems, leaves, cores, husks, seeds, skins…use your imagination!) 
• Crushed egg shells
• Natural unbleached yarn, twine, and string 
• Non-glossy paper products (cardboard boxes, black-and-white newspapers, mail, etc.)
• Tea leaves and bags (remove the staple!)
• Coffee grounds
• Dead plants, grass clippings, and dry leaves (make sure they don’t have diseases and have not been sprayed with pesticides)
• Non-treated wood products like sawdust and shavings
• Feathers and hair (human, cat, dog, etc.)
• Dryer lint

DO NOT put these in your worm bin:

• Citrus peels and juice (citrus makes the soil too acidic)
• Onions and garlic
• Fats, grease, butter, or oils 
• Meat or bones
• Plastics and plastic coated paper (like glossy magazines)
• Produce stickers
• Bread or yeast products
• Coal ash
• Salt, pepper, and other spices
• Milk or other dairy products
• Cat or dog feces (or any other kind of animal waste)
• Diseased or infested plants
• Treated wood products

Because worms can’t digest all kitchen scraps, many people keep both a worm composter and an outdoor compost system.

Troubleshooting Worm Composting Problems

A stinky bin is an indication that something’s not quite right in your vermicompost. The only smell your compost should have is the nice, earthy aroma of soil.

You may have one of these problems:

• Not enough worms: If you don’t have a critical mass of worms populating your bin, they won’t be able to digest your waste fast enough before it rots. You can add more worms, or simply slow down the feeding until your current worms reproduce and more hungry wrigglers are hatched.

• Too much food: Similarly to the issue above, you might simply be adding more food than the worms can eat. Cut down on feeding. Remember that your worms can digest 50–100% of their weight per day. Depending on the size of the bin, that’s only a couple pounds of food.

• Too moist: If your compost looks soggy, more like mud than fluffy soil, it’s too wet. The best fix for this is to add some brown material like paper or dry leaves. Add these around the corners of the bin to target where moisture collects.

• Too cold: Worms will slow down and even stop eating if they get chilly. If you notice that your kitchen scraps aren’t getting broken down (or that your worms don’t move much when you open the bin lid), try relocating your bin to a sunnier spot. Especially if you keep your home cool or your worm bin is outside, you can add cooked rice (slightly cooled) to the bottom of your work bin for food and heat. You can also shine a bright (non-LED) lamp on your worm bin to keep it warm.

Worms Escaping from Composting Bin

Worms may try to flee their bin if they don’t like the climate—if it’s too dry, wet, cold, or they don’t have enough food or oxygen. Make sure you are providing your worms with the right living conditions and there aren’t too many in the bin. Also check that your aeration holes aren’t getting clogged up, so your worms can breathe.

Remember that red wrigglers don’t like light, so another fix for escaping worms is to shine a light on the bin. They’ll stay inside, away from the brightness.

Infestation in Your Worm Compost Bin

Yes, other organisms will live with your worms. Most of the time they are friendly and won’t even be noticeable—including other bugs. But some other insects can cause a nuisance, like fruit flies and ants. 

To keep pests out and worms happy, be sure the moisture level is perfect—fruit flies are attracted to rotting food and too-moist conditions. If you continue to get infestations, try freezing scraps for 24 hours before you add them to the bin. 

And beware of centipedes, who may eat worms. If you see centipedes in your vermicompost bin, be sure to relocate them outdoors. 

Can you leave worm compost bins for extended periods?

Going on vacation? No need to hire a worm-sitter. Worms can last three to five weeks on their own as long as conditions are right. If the weather is cold, make sure the compost bin is in a slightly sunny spot for warmth (or add cooked rice as described above), add a little extra food, and have a great trip!

Alternatively, if the weather will be cool when you are away, you can simply let the room temperature fall below 55º, and the worms will go into a mini-hibernation-type state, waiting for you to return. Stop feeding your worms about a week before you leave so that there is no uneaten food rotting in the bin.

Just don’t let your worms get too cold—the can freeze to death! 

Advantages of Worm Composting

• Nature’s paper shredder: Instead of lugging your private documents and bills to the office store for shredded, cut up your papers and feed them to your worms. Identity theft doesn’t stand a chance again a worm’s appetite.
• Fun for kids: Kids love to watch the worms do their work, and classroom teachers can use vermicomposting as a valuable lesson in related ecosystems, responsibility, decomposition, and life cycles.
• Fishing bait: Red wrigglers are classic fish food! 
• Outdoor compost addition: You can also add worms to outdoor composting systems like a bin or pile to speed along your bigger compost operations.
• Apartment pets: Can’t keep a dog or cat in your home because it’s against your lease? Let worms be your companions. They’re soft too. Kinda