Raising eco-consciousness one week at a time

Friday, April 22, 2011

Composting with worms, without a backyard

Happy “Let’s make Earth Day Every Day” Day! ;)

Earlier this month, we gave you the many benefits of composting, including how it reduces your climate change impact. This week, let’s talk about how to make your own compost, even if you don’t have backyard space!

About Vermicomposting

Vermicomposting, or composting with red worms (Eisenia fetida), can keep your compost pile compact and contained, perfect for those living in an apartment or those who live in the mountains and want to compost indoors so as not to attract bears.

These red worms eat your leftover food and poop out a fantastic fertilizer. Worm castings (a.k.a. worm poop) make soil nutrients and beneficial microbes much more readily available to plants than regular compost. They're the best compost in the world!

Here’s a quick rundown of what you need to know to start your own vermicompost bin, in Q & A style.

Q: How do I get started?

A:  First, you need a worm bin (which is very different from a backyard bin). They are available online for anywhere from $50 – $200, BUT you can make your own bin for a fraction of the cost using an inexpensive plastic storage bin with a lid, like a 10-gallon Rubbermaid® Roughtote® storage box (pictured) using these guidelines:

  • You want to match the size of the bin to the amount of food scraps you generate. A typical storage box is a good fit for a two-person household. Allow 3 square feet of surface area in your bin for every pound of food scraps you generate per day, and any bin should be at least 10" deep.

  • Worms require darkness, so you need a lid.

  • Worms also need oxygen, so drill five holes on top and five holes in the bottom using a quarter-inch drill bit for every square foot of feeding surface area inside.

  • The holes on the bottom will also serve to drain excess moisture (make sure they are at the low point!), so you need something under the bin to catch the leachate. It can be another container of the same size and shape as the bin on top.

  • Don’t use treated wood or toxic finishes to build your bin.

Q: Where can I buy worms?

A: We recommend purchasing worms locally by heading up to Fort Collins to meet our local worm expert and Eco-Cycle® supplier, John Anderson (970-407-9076). A pound of worms (roughly 1,000 worms) is a good start for most households. You can also find several worm growers online if you search for “compost worms.”

Q: I have all my supplies. What’s the first step?

A: Have your bin ready before the worms arrive. Create a layer of bedding several inches thick using strips of moist newspaper. Mix in a small amount of soil or finished compost for the worms to ingest into their gizzards—they need this to digest their food. Then add a small amount of food scraps and watch them go to work!

Q: How do I know when it is okay to add more food? What can I do to make sure my compost stays healthy?

A: Use your nose! A healthy worm bin should smell like fertile soil. When feeding, don’t get too far ahead of the worms, especially when establishing a new worm colony. Wait until you see more castings (which look like dark, rich soil) than food at the top of your bin before you feed them again. Under good conditions, a worm can eat about half its weight per day. So, if you just bought a pound of worms, be patient and let the population grow. Worm populations can double every two months under ideal conditions.

If your bin smells overwhelmingly of rotting food, you are probably feeding your worms faster than they can eat. Remove excess food so you don’t have more than a one-inch layer of food in your bin and keep an eye out for mold—worms won’t eat food once it spoils. The moisture level of your bin is also very important; make sure excess water is draining out of the bottom of your bin.

The best advice is to stay attentive. Don’t be afraid to gently rummage around in your bin to assess conditions. You are maintaining a whole ecosystem of critters when vermicomposting; the worms are just the most visible inhabitants. If the worms are climbing the sides of the bin in large numbers, they are trying to tell you that conditions aren’t right. Channel your “inner worm” and trust your instincts—you’ll keep everybody happy and healthy.

Q. How do I harvest the castings?

A: Worms live in the layer between finished castings (below) and food scraps (above), so unless you invest in one of the “worm condo” models that have drawers that can be removed once filled with finished castings, you will need to temporarily remove the worms and the layer of partially-digested food to get at the finished castings below. Keep in mind that worms respond to light by burrowing down (and faster than you might think), so make sure you are ready before you lift the lid. You’ll need a place to put the worm/food layer (the lid or a tarp), a container for the finished castings, a small garden fork, and a trowel.

   1. Remove the worm/food layer. Worms create colonies, so the less you disturb them when harvesting, the faster they can recover. Scoop out this layer as intact as possible and set it aside carefully.  Do not put it directly on the floor—you’ll sacrifice too many worms trying to pick it up later. A garden fork works best to do this because it will pick up the undigested food and leave the finished castings. If you are leaving a lot of worms, go deeper. Expect to remove a layer about four inches deep.

   2. Remove the castings. You may want to switch to a trowel for this step. You will probably see some worms down in the castings layer, but more than 90% of them should be in the food layer.

   3. Put the worm/food layer back in the bin, again as intact as possible to minimize disturbance.

   4. If you feel that too many worms are left in the finished castings, you can recover them by piling up the castings in a conical shape. Gradually skim a layer of castings off the cone as the worms burrow away from the light. (Hint: a strong light or bright sun makes this go faster.) When you start to see worms again, back off and wait for them to burrow further. If you are patient, you will eventually end up with a small pile of worms at the very bottom and a big pile of worm-free castings. (But, don’t be TOO patient. Finish this process in a few hours at most and get the worms back in the bin.)

Q: Won’t the bin get smelly? And what about fruit flies? Will animals be attracted to my bin if it’s out on the porch?

A:  Your compost won’t stink as long as it stays healthy. A small population of fruit flies is inevitable, so the best way to minimize this issue is to keep your bin outside. If you want to keep it indoors, choose a place where you can tolerate a few flies. You can keep their population in check by avoiding overfeeding the worms, which limits the amount of rotting material available for the flies to lay their eggs. Fruit flies also prefer a slightly acidic environment, so if you have more flies than you can tolerate, cut back on the amount of citrus, coffee grounds and other acidic foods in your bin. Or, build your own fruit fly trap (pictured).

Your worm bin is definitely a potential food source for animals like squirrels and, yes, even bears, if left outdoors. You’ll have to judge for yourself the level of bear activity where you live. If bears aren’t regular inhabitants of your neighborhood, you may be able to leave your bin outside undisturbed for much of the year and only bring it indoors in late summer and fall when bears are loading up on calories for hibernation. Squirrels are usually deterred by a good-fitting lid. Raccoons may be the most difficult to deter because they are so dexterous and persistent. If you see tooth marks on your bin or other evidence of a raccoon visit, bring your bin inside for a few weeks.

Have a question we didn’t answer? Check out “Composting in Apartments & Bear Country,” from the Eco-Cycle Times archives, or ask us below!

Next week, we’ll give you everything you need to know to start a backyard compost pile.


  1. LOL "Channel your inner worm". This posting was so helpful - you made it simple and easy - I guess I'll try doing it.

  2. Everyone should channel their inner worm.

  3. Hi, who can I contact about using the worm photo in a print publication?

  4. Hi Kristine,
    The photo is from an online stock photo website, either istockphoto.com or shutterstock.com. There is a small charge to use photos from these sites.
    - Iris