The DIY Worm Farm: How to Make a Worm Bin

Want to learn how to vermicompost? Start your DIY worm farm by sourcing your worms and building a worm bin for your little wriggling composters.

Worms eat kitchen scraps and create worm castings, which are a valuable soil amendment and plant tonic. Though castings are often called fertilizer, they’re actually not very high in nitrogen, but they are full of plant-supporting nutrients.

Sprinkle castings on potted plants and over garden beds. A little goes a long way. A handful can go into the bottom of a planting hole to get a plant off to a good start. Unlike nitrogen-rich fertilizers, worm castings won’t burn the plant’s roots. They can also be mixed with potting soil, in concentrations of up to 20 percent castings, to make an extra-rich growing medium.

Here’s what you should know before you start: A worm bin is a supplement to a compost pile, not a replacement for one. Worms don’t consume indiscriminately the way a compost pile does, and they can only eat so much at a time. But, as we said above, castings are a fantastic resource, so it’s well worth keeping both a worm bin and a compost bin. That said, a worm bin makes a fine green-waste disposal system for an apartment dweller. If you don’t have yard trimmings to worry about, worms can handle a good deal of your day-to-day food waste — such as coffee grounds, wilted lettuce, stale bread and so on — and give you castings in return that you can apply to container plants.

Worm bins are best kept indoors. Worms thrive in temperatures between 50 and 75 degrees Fahrenheit, and those conditions are usually found in the cool parts of a house instead of outdoors. During hot summers, worms dig down deep to keep cool. They can’t do that in a worm bin, which will heat up to ambient summer temperatures. In winter, freezing cold will kill them, too. Of course, it all depends on your climate and situation. If you have cold winters and mild summers, the worms could spend the summer outdoors and the winter indoors. Or in the opposite situation, they could come in for hot summers and stay out for mild winters. You can also take steps to keep the bin’s temperatures reasonable, such as insulating it. Just remember that when temperatures are extreme, worms are unhappy.

Sourcing Your Worms

While you can buy worms from online suppliers, it’s more fun to get them from a friend who keeps worms or to hunt them in your own garden. Worms from a friend are truly local and already well-adapted to life in a worm bin. In addition, they’ve not undergone travel stress. Mail-order worms are understandably freaked out on arrival (as freaked out as worms can be) and will often try to escape from the bin their first few nights before they’ve calmed down.

It’s most satisfying to hunt worms in your garden. The worms you want aren’t the big, fat night crawlers; they’re the smaller red or purplish worms that live close to the surface of the soil, usually in leaf litter or in cool compost. They are most populous in spring and fall and can be hard to find in summer and winter. Make a trap for them by burying something tasty in your garden beds or in an area rich with leaf litter. Worms adore squash. It draws them like a magnet. You could also use leftover oatmeal or wet bread. Bury these offerings about an inch under the soil or leaf litter and come back in about three days. More than likely, you’ll find some worms bellied up to the bar. Scoop them up and take them to their new home.

Worms are hermaphrodites, so they’re not picky about mates. They breed at a rate that puts rabbits to shame. If you’re willing to be patient, you only need to hunt up about a cup of them to get started. If you buy them, you’ll buy a full pound — that’s usually the minimum amount on offer. Whichever way you go, it all works. More worms eat more scraps and make more castings. If you start with lots of worms, the bin will be productive faster. If you start with only a handful of worms, they’ll start breeding as soon as they settle into their new home, and you’ll be up to speed in a couple of months.

Which Worm Is Which?

Red worms (Lubricous rubellas) are the worms you most often find in leaf litter and garden beds, but they also hang out in compost piles. Compost worms (Eugenia fetid) are about the same size and can be red, too, but they also come in purple and tiger-striped varieties. These are true compost worms whose preferred habitats are compost and manure piles. Eugenia fetid is the type sold for worm bins, but Lubricous rubellas adapt to life in the bin very well.

Make a Worm Bin

Although you can buy or build elaborate multilevel worm composting systems, we’ve come to believe less is more when it comes to worms. A simple container is all you really need.

Preparation: 1 hour

Supplies:

Power drill or a sharp nail and a hammer
Rectangular plastic storage bin with a lid, any size
Newspaper and cardboard
2 cups ordinary soil, any type
Red worms (Lubricous rubellas) or compost worms (Eugenia fetid)

Instructions:

Using the drill or the sharp nail and a hammer (the latter is much more difficult — use a drill if you can), create two rows of ventilation holes around the top edge of the bin, starting beneath the lid. Space the holes about 3 or 4 inches apart. The exact size of the holes doesn’t matter much, but they should be 1/4 inch or less in diameter. To make sure the bin doesn’t leak and can be kept anywhere, don’t put any holes in the bottom of the container. Lack of bottom drainage means you’ll have to be vigilant to make sure the contents don’t get too soggy, because there’s nowhere for water to go.

Shred newspaper into fine strips. Use plain newspaper, not shiny inserts, which may contain harmful dyes, and not office paper, which has been bleached. If you have a paper shredder, run the newspaper through that, because the finer the paper shreds, the better. Otherwise, rip the paper into strips. While you’re at it, rip up some plain corrugated cardboard, too, if you have it. It must be bare cardboard, not paper coated, because again, that paper may contain bleaches or inks. It’s easier to rip up cardboard that has been soaked in water first. Worms really like corrugated cardboard — they snuggle up in the channels, so tear it into worm-size chunks roughly 4 inches square.

Wet the newspaper strips by placing them in a bowl or bucket and drizzling water over them and stirring until they’re all equally damp. Add the shreds to the worm bin by the handful, squeezing them first to make sure they’re damp, not sodden. The ideal consistency is that of a wrung-out sponge. You don’t ever want to have standing water in the worm bin.

After you’ve added about 4 to 6 inches of newspaper to the bin, add the cardboard pieces and about 2 cups of soil. The soil adds grit to the mix, which helps with the worm’s digestion. Toss it all together to mix it. Add the worms. Put a little paper over them right away, because they don’t like the light.

Feeding Worms

Theoretically, worms can eat their weight in food scraps each day, but in practice, the amount they eat is highly variable. One factor is newness. A new bin doesn’t eat nearly as much as an established bin, no matter how many worms you start with. It may take a few months for a bin to hit its stride and become an eating machine. In the meantime, don’t overfeed. If you add more food than the worms can handle, it will lead to bad smells and possible invasions by undesirable insects.

Start off with just a cup of scraps on the first day. See “What to Feed Worms,” below, for suggestions. Bury the scraps in one corner of the bin and cover it with about an inch of newspaper. The worms will find the food. After a couple of days, add another cup of scraps in another corner. Proceed cautiously, even if you have lots of worms, because they may not want to eat much at first. Develop an intuition for what is enough and what is too much. While it’s important to feed them plenty if you want them to breed, don’t worry much about them going hungry. If they get hungry between feedings, they’ll eat the newspaper. Eventually, they’ll eat everything in the bin. All of the newspaper, cardboard and food scraps will be reduced to black gold: worm castings.

What to Feed Worms

Worms aren’t hamsters. They don’t rush to nibble your fresh offerings. Instead, they work in concert with fungi and bacteria to break down rotten food. If it’s not rotting, they’re not interested. That’s why it usually takes a couple of days before they approach new food. Overall, they prefer soft food, such as oatmeal and squash, to hard food, such as carrots. Of course, even carrots will rot eventually, and the worms will get to them then. Don’t put large chunks of food in a worm bin. Take a moment to rip or cut food scraps into small pieces to speed decomposition.

Worms don’t eat vegetable seeds. Nature designed seeds so that they don’t break down easily. More often than not, the seeds will end up mixed in with the castings and thus could sprout wherever you spread the castings. If this concerns you, separate out seeds before you give food to the worms. Send seeds to the compost pile instead.

Worms like to eat:

Coffee grounds and tea leaves
Crushed eggshells
Dry cornmeal, just a sprinkle, as a treat
Fruit of all sorts, except citrus
Lettuce
Oatmeal and other cooked grains
Squash
Wet bread and bready things like cooked pasta

Worms will eat:

Just about any chopped vegetable matter, fresh or cooked
Newspaper and uncoated cardboard
Rabbit droppings

Don’t feed worms:

Citrus of any sort (It’s antimicrobial.)
Dairy (Traces are OK.)
Meat
Oil
Salty or processed food
Sugar (Traces are OK.)
Vinegar

Maintaining the Worm Bin

Put the bin in a safe, quiet place out of direct sunlight, otherwise the sun will shine through the plastic walls and irritate the worms. Wherever you stow the bin, be sure the temperatures are moderate. Keep the lid on tight if you have dogs in the house — canines don’t have discriminating palates. Our dog once nosed off the lid on our worm bin and ate half of the contents before we stopped him. We don’t know whether he was more interested in the worms or the rotten food, but he swallowed it all. If your bin is outside, lock down the lid with a bungee cord to keep raccoons and skunks and other insectivores out at night. And heaven help you if a wandering chicken ever came across your open worm bin!

Aim to keep the contents of the bin always at that magic consistency: moist as a wrung-out sponge. In the first few weeks, you may have to use a spray bottle to mist the paper to keep it from drying out. Worm castings hold water, so when they appear, the bin will stay wet on its own. Your challenge then becomes keeping it dry enough. It’s important that it stay a damp, airy environment. If it seems to be getting soggy and dense, mix in a few handfuls of dry shredded newspaper to dry it out and fluff it up. If lots of worms are hanging out on the sides or lid of the bin — or trying to wiggle out the air holes — it’s definitely too wet.

Note: Keeping the lid on the bin keeps out the light and also keeps out flies. However, it holds in a lot of moisture. If you’re having trouble keeping the bin dry enough, you could cut a window out of the lid, and then use duct tape to secure a piece of window screen over the hole. That way, you have both air and protection. If you do this, keep the bin in a dim place for the worms’ sake.

The deeper the contents of the bin, the greater the danger of the bottom portion of the bin turning swampy and anaerobic. To prevent that, don’t let the contents of the bin get too deep. Keep the depth of the contents between 6 and 8 inches and you should be fine. If you have a ton of worms and 6 to 8 inches doesn’t seem like enough room, it’s time to start a second bin, give your extra worms to friends who want to start their own bins, or feed some spares to your chickens. You could also distribute a few handfuls in a cool compost pile.

Don’t be afraid to dig around in the bin every so often to make sure all is well. Check regularly to be sure there’s never any standing water in the bottom of the bin. Bad smells will ensue, and worms will die. If all is well, eventually you should see tiny baby worms in the mix, as well as the little lemon-shaped beads that are worm cocoons. These are good signs. Your worms are happy and breeding. As your bin matures, you may find that other critters — decomposers such as mites, pot worms and tiny black beetles — will make it their home as well. This is nothing to worry about. They’re all doing the same work, and the worms don’t mind the company.

Before you go on vacation, feed the worms well and add fresh bedding. They’ll be fine for a couple of weeks.

Harvesting the Castings

When the contents of the bin start looking more black than anything else, it’s time to harvest some castings. This will probably happen about two months after you start the bin. The simplest way is to stop adding fresh food for a while and let the worms finish up the little scraps and bits dotting the bin. When there’s not much recognizable food in the bin, put a big portion of something delicious — a proven favorite such as squash — at one end of the bin. The worms will migrate that direction. Wait a few days, then scoop out the material on the opposite side of the bin and pile it on the bin lid. Do this during the day or under bright lights. Form the pile into a pyramid or cone shape. There will still be worms in the mix, and they’ll dive down to the bottom center of the mound to hide from the light. You can then harvest the castings from the top and sides of the mound and transfer them to a bucket or bowl. Return the worms hiding at the bottom of the pile to the bin.

Add fresh wet newspaper and soil to the bin, just as you did at the beginning, to rebuild after harvest. Mix this material with the remaining material and start feeding normally again.

Freshly harvested worm castings are very wet. Spread them out on a tray and let them air-dry for a few days, and then sift them through a screen or colander. This will catch any remaining food scraps and give the castings a nice granular texture that’s easy to spread. Store them in a bag or covered container.

Worm Tea

One excellent use of castings is in a liquid plant tonic. Put 1 pint of castings in a bucket. Add a gallon of warm water and a spoonful of molasses. Stir this well, and stir it frequently over the course of 24 to 48 hours. Dilute the resulting liquid at the ratio of 1 part tea to 4 parts water and use it to water container plants and fruit trees. You can use it in your vegetable beds, but they should already be well nourished by compost and thus don’t need it as much. It’s best to use all of your worm tea in a week or so.