Care and Feeding of a Worm Bin

There are tons of resources on the web about vermicomposting (I've included links to some good ones below). These are just my thoughts based on my personal experience.

Plus, a separate page on Building a Tiered Worm Bin

Bedding

"Bedding" is a bit of a misnomer, because worms will eat their bedding. The thing that distinguishes "bedding" from "food" is primarily that a good bedding material doesn't smell, get moldy, or attract bugs as much as food does, and therefore is good to cover food with. It also fills the gaps between drier food, such as carrot peels, which helps the worms travel and keeps the food moist so it breaks down and is edible by worms. It also helps break up heavier masses of wet foods, such as the carrot pulp from your juicer.

  • Coffee Grounds - my favorite worm bedding

    Some people say coffee grounds are too acidic for worms. I don’t think that’s true at all. My first experience with vermicompost was in a regular compost bin. I used to add garbage bags-full of coffee grounds I got from my local coffee shop, and soon, worms had moved in on their own. It was really an “If you build it, they will come” experience.

    You can often get coffee grounds from your coffee shop, and Starbucks has a program called “Grounds for the Garden”, where they will pre-bag them and set them out front. If they are not set out (I find it’s less common in the city and in winter), the staff are usually happy to just give you the current garbage bag of grounds. I actually prefer that, because they usually remove the filters when they pack it, and I like to use filters (more on this below). Please consider leaving a tip for the staff if you get grounds from a coffee shop.

  • Shredded Paper and/or Cardboard

    I always start with a layer of this. Besides the usual benefits of bedding, paper prevents the other stuff (e.g. coffee grounds) from falling through the drainage holes.

    Many types of paper that can't be recycled are great for worm bedding, e.g. dirty pizza boxes, cardboard boxes that are contaminated by food or liquid, or uncoated paper take-out containers. Tear them into pieces and soak in water if they are dry, before putting them in your bin.

  • Paper Towels, Napkins, Tissues, Coffee Filters, etc

    Softer, thinner paper products are great on the top of the bin because they help keep the bedding moist and suppress mold, fruit flies, and other unpleasant aspects of a worm bin. After laying them on top, sprinkle them with water to moisten them and make them stick to the bedding/food. Obviously, don't use paper that is contaminated with toxic products, such as disinfectant or bleach.

  • Coir

    Commercially sold worm bins often come with coir for bedding. I don’t know why; they must have a deal with the coconut industry. It doesn't seem to break down or get eaten, so when you harvest your worms you always have to deal with clumps of coir. I never want to see coir again.

Food

For the most part, any organic matter can be eaten by worms. (Try to avoid too much salt, fat, or spicy food.) In general, the smaller and softer the food is, the easier it is for worms to eat. Some people cook raw scraps and process them in a food processor, but that's way too much work for me; I believe in letting the worms do the work. Still, sometimes it’s easy, for instance, to add the tough broccoli stalks to the steamer, and I’ll do that.

  • Citrus

    Many sources say that citrus peels are not good for worms. I usually put citrus in my regular compost bin instead. However, I also find worms in the regular compost bin, so, as with everything, the dose makes the poison. If you have a lemon tree constantly dropping moldy lemons, you probably shouldn’t put them in your worm bin, but the worms will be okay with an occasional peel.

  • Onions, garlic, peppers, etc

    Similarly, many sources say to keep these out of your worm bin. And again, I put them in my regular compost bin and still have plenty of worms in there.

  • Salty food

    Salt is definitely bad for worms, but again, I’ve added old food that had salt (in moderation, like old hummus, but not leftover Chinese food or potato chips). Salt is also not good for the garden, so if it’s very salty, best not to add it.

  • Tomatoes

    As with coffee grounds, some people claim that tomatoes are too acidic for worms. I don’t find this to be true either. I have tossed lots of tomatoes into the worm bin with no apparent ill effects.

  • Egg Shells

    Yes, worms will even eat egg shells, but rather slowly, and only if they are crushed pretty fine. However, egg shells are good for your soil, so even uneaten egg shells will enhance your compost. Egg shells also add grit to your worms' diet, and help neutralize acids, so they are good to add (crushed). I usually put them in a paper bag and roll over them several times with a rolling pin; still, I often find pieces of shell when harvesting vermicompost.

  • Corn Cobs

    Worms LOVE corn cobs. If your worm bin is a Ritz-Carlton hotel, corn cobs are the Presidential Suite. I break the cobs in half or thirds, and stick them in the bin. Worms will hollow out the core and move in. It takes a little longer for the entire cob to breakdown, but I just move uneaten cobs (plus whatever worms are hiding inside) from one tier to the next when I'm harvesting.

    They also eat the husks, but that's just another food.

  • Growing Seedlings

    Vermicompost is an excellent germination medium, so after tossing tomatoes in the bin, I get lots of tomato seedlings sprouting in my worm bin. I’ve also gotten squash seedlings. I sometimes cook/nuke my squash seeds to (hopefully) make them more palatable to the worms and prevent them from sprouting in the worm bin. I should probably consider that for the tomatoes as well.

    On the other hand, if you're a curious gardening type, you can take the seedlings from the compost bin and plant them to see what you get. (I've done this a lot - everything is a science experiment.)

  • Favorite Foods

    If, like me, you start to think of your worms as pets, you might consider their preferences when grocery shopping. At a minimum, knowing the worms will eat it may make you feel better about eating foods that generate a lot of refuse. Here are some of the foods that I've noticed my worms like:

    • Figs (Ok, I'm not saying buy figs for your worms - I have a fig tree and the worm bin gets the ones that are partially eaten by birds or squirrels, go moldy before I pick them, etc. But every time a bunch of figs gets dumped in the bin, a few days later it's like a big worm orgy in the bin; I think they are a worm aphrodisiac.)
    • Artichokes
    • Corn (cobs)
    • Melon rinds

Water, Air and (Un)Natural Disasters

A good worm environment should be damp, but light and loose, like coffee grounds after brewing is completed. Keep the bedding moist, but not wet. If you stick a finger in and nothing sticks to your finger, it's too dry; if it feels like mud, it's too wet. I used to water mine, but I found that, once it was well-established, added moisture was generally not necessary. This may depend on how wet your food is. Your bin should have drainage holes to keep it from getting too soggy, but you have to make sure to empty the drip basin (unless it drains directly into the ground). If you let the water build up, your worms will drown.

Even with drainage, the compost can get too wet or compacted if you are adding too much dense or wet food without lighter, airier bedding (like shredded paper) to break it up, or if the total weight of your bin is too heavy and putting too much pressure on the bottom material. If the compost gets too compacted, the worms will move up before they have finished eating all the material, and the composting process will go anaerobic and get smelly. I recommend keeping the total height of the material in all tiers under 20" (10" per tier), less if your material is dense. If you are using 5-gal buckets, fill them no more than halfway before switching to a new bucket.

Harvesting Worm Poop

I tend to be a bit compulsive about separating my worms from the compost when harvesting. While worms can survive in the garden, of course, the worm bin is a much nicer environment for the worms, so I try to save as many as possible to put back in the worm bin. Here's how I separate my worms:

  • On the patio, in sunlight, lay out a large piece of plastic (usually a large empty bag from potting soil or similar).
  • Take a cup or two of compost from the bin, and form it into a sort of cone or hemisphere shape on the plastic.
  • Repeat for as many as you can fit on the plastic.
  • Let it sit for several minutes (if you are doing a lot, by the time you've finished the last pile, the first pile may be ready.) Do not leave for too long, as vermicompost becomes very hard when it dries out.
  • Gently scoop compost from the outside (I usually use a plastic spoon for this). The worms will have moved away from the exposed sides toward the middle, and the scooping will further push them to the center.
  • When you start to see worms, move on to the next pile. When you have finished all the piles, go back to the first.
  • Repeat until you basically have a pile of worms. Put them back in the bin. Use the compost in your garden.

Using Vermicompost

As noted above, vermicompost becomes very hard when it dries out completely. Even soaking it in water will take a very long time to soften it up again, so it's best not to let that happen. When using it in the garden, work it beneath the surface and mix well with garden soil to avoid hard clumps forming.

Links to Other Sites / Troubleshooting Problems

Here are some links to other vermicomposting sites, some with good troubleshooting tips: