Composting 105: Indoors with worms

Red wiggler worms make great compost
Photo by Susan Levi-Goerlich

Susan Levi-Goerlich, a University of Maryland Extension Master Gardener and a member of the Howard County Master Gardener Compost Education Committee, answers questions about worm composting, also known as vermicomposting.

Why compost with worms?

Susan: Vermicomposting is perfect for people who don’t have the space for an outdoor compost pile or bin. It’s inexpensive and requires no physical activity. It’s also a great project for kids. Little kids love worms and older kids will never lack for science fair projects if they have a worm bin at home.

How do you set up a worm bin?

Susan: Take 2 opaque plastic bins, preferably 10 gallons each. Drill holes in the bottom of one of the bins—about twenty-four ¼-inch holes. Drill a couple of holes near the top edge of that bin. Take the second bin and drill about 8 holes on the side of the bin, about 2” up from the bottom. Set the first bin inside the second bin. There are also commercially produced bins available if you don’t want to make your own.

Three of Susan’s vericomposting bins
Photo by Susan Levi-Goerlich

Shred newspaper and briefly soak it in water. Squeeze most of the moisture out of the paper (until it is as wet as a wrung out sponge) and add the paper to the bin, so that the bin is about a half to 2/3 full when you fluff the paper. Add fruit and vegetable scraps by burying them under the bedding. Add worms. Cover the bin. That’s it.

Do you need a special type of worm?

Susan: Yes. Red wiggler worms (Eisenia foetida) are particularly well suited to living in bins because they do not tunnel deeply or make permanent burrows. Do not use night crawlers or try to dig up worms from your garden to put in the bin. Most worms would not be happy living in a bin, and if they are not happy, they will not stay in the bin!

You’ll want about 1,000 worms—one pound—to begin with. Red wiggler worms are available from many sources on the internet, and if you have a friend with a worm bin, it’s quite likely she will share some worms with you.

Should my worm bin be inside or outside?

Jane H., Diane B., and Bettye A. set up
large vermicomposting demo bin
Photo by Susan Levi-Goerlich

Susan: Red wigglers prefer temperatures between 55° and 77° F. That makes them very well suited to living in the house. In Maryland, our hot, hot summers and cold winters make it difficult to keep a worm bin outside or in a garage, so you should try to find a nice quiet place to stash the worm bin.

I’ve heard of bins being kept in kitchens, basements, cabinets, and closets. I currently have four worm bins in my basement closet. We have an outdoor worm bin at our demonstration site at Schooley Mill Park, but the bin is very large—about 4’x8’—and set about two feet into the ground.

How big should the bin be?

Susan: Ten gallons is a good size. Larger bins get very heavy as you add lots of food scraps, and smaller bins are hard to manage efficiently.

What should I feed the worms?

Susan: The worms love fruit and vegetable scraps. Freeze the scraps for at least 24 hours to kill any fruit-fly eggs or larvae and then defrost the food. Drain it and then add the scraps to the bin and cover with a handful of dry shredded newspaper. Tea bags and coffee grounds and filters also are good additions.

Are there things I should not feed the worms?

Susan: Don’t feed them meat, dairy products, fats, or oils. However, eggshells are good for the worms. I don’t add orange peels because I’ve heard that they contain a substance called limonene, which is bad for the worms.

How often should I feed the worms?

Susan: Once or twice a week is good. A 32-oz. yogurt container full of food scraps is about the right amount. As your worm population increases, you can increase the amount of food you give them. The population will increase if the food is plentiful and decrease if the worms need to compete for food. Don’t overfeed the worms because the excess food can make the bin smell.

How long does it take to produce vermicompost?

Susan: You’ll start to see castings within the first week. The bin will be ready to harvest in three to four months.

How do you harvest the castings?

Susan: There are several ways of separating the worms from their castings, the vermicompost.

Susan’s daughter uses “little piles” method
to harvest vermicompost
Photo by Susan Levi-Goerlich

My personal favorite is the “little piles” method. I spread a tarp out on the floor and make little pile with handfuls of the contents of the worm bin. I shine a light on the little piles and go away for about an hour. The worms don’t like the light and they’ll dive to the bottom of the pile. You can then reach in and remove a ball of wiggling, squirming worms, and put them back into the bin along with fresh shredded newspaper and food. Unprocessed food can also go back into the bin. What remains is your vermicompost. You should allow at least an hour to harvest with this method.

My second favorite way of harvesting, and one that is less work intensive, is the vertical migration method. I take a new bin, drill holes in the bottom of it—as though I were starting a new worm bin—and put it on top of the existing bin. I then add fresh shredded newspaper and begin feeding in there. Many of the worms eventually migrate to this new layer and leave behind their castings. I can add additional bins as necessary. Most of the commercially available bins rely on this system.

The least work-intensive method is to simply take about 1/3 of the contents of the bin and put it right into your garden. You’ll lose a fair amount of worms this way, but in time the population of the bin will build back up.

What are some uses for vermicompost?

Susan: You can use it on your house-plants or in your garden. I usually add a scoop of worm poop to the hole when I’m transplanting seedlings into my vegetable garden. You can make compost tea to use on your ornamental plants.

Additional Information: To read Susan’s comprehensive document on vermicomposting, CLICK HERE

To link to the University of Maryland Extension’s free 2-page brochure, “Indoor Redworm Composting,” HG40, CLICK HERE.

To see the schedule and locations of composting demonstrations by Howard County Master Gardeners, CLICK HERE.

3 Comments on “Composting 105: Indoors with worms

  1. we have a very small one (maybe 1 1/2 gallons) for the boys to care for and feed. We love it and I can't believe the amount of breeding going on in there! There are eggs all around the bin and worms at various stages of life. We sometimes add a few worms to our outside compost and they seem to thrive there too. Thanks for the (com)post!


  2. If you and your boys are enjoying your very small bin, you might want to graduate to a somewhat larger bin. It's really easier to take care of!


  3. I am planning to start a bin in my kitchen and I'm wondering if there is anyone locally that might be willing to share some worms. I was hoping to find a local source yesterday at the GreenFest at HCC but didn't see anyone with info. I can be reached at


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