Vermicomposting is an indoor composting technique where you keep a worm bin and let the worms do their good work in converting newspapers and kitchen scraps to “worm castings.” This form of finished compost is incredibly high in rich microbial life (the basis for nutritional exchanges in the soil) and rich in nitrogen. Its a perfect soil amendment for organic gardening of all kinds (or house plants if you aren’t actively gardening). About a year ago, one of my friends lead a workshop for our Permaculture Meetup on Vermicomposting; I supplied all the materials, and I ended up with a great worm bin. I fed it religiously for the first few months in the winter, sporadically after that, and, honestly, forgot about it for the last two months with the flurry of end-of-semester activity. Recently, I opened it up to harvest the castings and refill the bin–the worms were still happy as could be and had produced an amazing compost!
Vermicomposting is one way that people in apartments or other small spaces can compost without worrying about having the outdoor space for a compost bin–you can add the compost to plants grown in pots or buckets, and have a small-scale patio garden operation!
Vermicomposting is also particularly useful for the colder months of the year. In December-February most of my food scraps will freeze if I throw them in a pile (and even sometimes, if I throw them to the chickens and the chickens choose not to eat them). The worms are a perfect way to use those scraps and keep your compost moving and getting different kinds of compost year round (for other composting methods, see this post).
I also like the earth-centered energetics of the worm bin. The humble earth worm, with a strong presence in your kitchen, brings excellent earthy qualities. The idea that the soil web of life is happening right there, before your eyes, is a very magical experience. I could also see this as a great way to educate children about the cycles of nature and our incredible soil web of life.
Building a worm bin is very simple, and probably can be done with materials you likely already have around your home (we built mine by finding materials in my garage). You can buy fancy expensive worm bins (usually running about $100 or so), but I think its much more fun and sustainable to build a bin out of what you already have. You can also often find cracked plastic tubs on the side of the road–a cracked tub would be fine for the inner bin.
Materials for the Bin: Here’s what you need to build the bin:
- 2 plastic tubs. One tub will need to fit in the other, and the inner tub will need a lid. The tubs should be opaque (the worms like it very dark).
- 2 “supports” 3-4″ high. I used plastic deli containers, but you could also use bricks or stones.
- A drill and largish-drill bit (like 1/4″ or so).
- Bucket of water.
- Worms and food scraps (covered later in this blog post).
How to build your worm bin:
1. Start by placing your supports in between the inner and outer tubs. Your supports should hold one tub above the other about 3-4.” See my photo below for more information.
2. Once you know how high your inner tub will be, you need to drill holes. You will drill holes around the top edge as well as in the lid for air flow in and out of the bin. You will also need to drill holes in the bottom for drainage (the worms sometimes produce a “compost tea” that will drain into the bin and that can also be used for plants.
3. Once this is done, add your supports and put the inner bin inside of the outer bin.
4. Now its time to fill the bin! Tear your newspaper into strips. Try not to tear too many sheets at once–you want to pull the sheets apart, tear them up, and then crumple them up.
5. Add the strips to the bucket of water and soak for a few minutes.
6. Add the soaked newspaper strips into the inner bin–you want to fill the bin 1/2 – 3/4 of the way full with the newspaper. You can also add a bit of soaked cardboard or paper towel tubes if you have them–the worms will eat through pretty much any paper product.
7. At this stage, your bin is ready to accept food scraps and worms!
Worms. Most indoor vermicomposting does not use typical earthworms found in, say Michigan, but rather worms called “red wrigglers.” If you have a friend who has a worm bin, they can just give you a handful of their works–that’s how I got mine originally, and a small handful of worms quickly multiplied. If you don’t have friends with worm bins, you can order them online (just google “red wrigglers.”) They run about $15-30.
Food Scraps. Worms can only digest certain kinds of food scraps–mostly vegetable in origin. Here’s what you can’t put in a worm bin:
- Meat and bones
- Citrus (the acidity of the lemon or orange peels can irritate the worms)
- Eggshells (I learned this one the hard way–they don’t break them down)
- Anything sprouting, like a sprouting potato peel (the worms tend to avoid eating living things)
Feeding your worm bin. Depending on the size of your family and the amount of vegetables you consume, one worm bin might not be sufficient for all of your composting needs. What you want to do is start on one side of the bin, pull back the newspapers, and bury a small handful of food scraps within. The next day, you can move a few inches around the edge of the bin, and add another handful. In about a 2-3 week period, you can work your way the whole way around the bin, burying food in many areas. By the time you work back to the original spot, the worms should have taken care of that section and you can add more food. If you add too much, just give the bin a week or so before adding more scraps. When you are getting ready to harvest your worm castings, you probably want to let the bin sit about a month so that the worms can take care of the last of the food scraps–then they will move to working on the newspaper and break that down.
Harvesting and refilling your worm bin. I waited about 9 months to harvest my worm castings for the first time, but I know I could have probably harvested them a bit sooner. What I did was take a small spoon and pull the castings up from the bin, checking them for worms, and then putting them in a separate bucket. Any worms I found went into another bowl, that eventually went back into the bin. I didn’t harvest 100% of the castings–I left about the bottom inch (which still had some newspaper) in the bin. That last inch had the highest concentration of worms anyways. After I had harvested my castings (probably 3 or so lbs of them) I refilled the bin with wet newspapers (just like I described above) and began adding food scraps again. I think if you had a few bins, you could get them on different harvest schedules and have castings more often.