It may be doubted whether there are many other animals
which have played so important a part in the history of the
world as these lowly organised(sic) creatures.
CHARLES DARWIN on EARTHWORMS, 1881
Everyone’s heard of a back yard compost pile, but did you know you can create even richer compost if you let worms break down your organic waste instead of just microorganisms? Composting with worms, or vermicomposting, yields a compost that gives soil better moisture- and nutrient-holding properties than standard microbe composting. This is due to the mucous worms leave in compost as they eat; the mucous keeps nutrients from being washed away with rains.
Vermicomposting also naturally and continuously produces compost tea, a rich liquid form of compost.
The worms you want to use are called red wrigglers, and they work best because as they eat, they leave castings (manure) that contain many times more nitrogen, phosphorous, potassium and other valuable nutrients than standard soil. Red wrigglers are available from bait shops, but it’s usually better to get them from vermiculture (worm-breeding) farms or shops, where they’re generally cheaper and healthier. Before you go buying worms, though, you’ll need to set up your vermicomposting bins.
Setting Up Vermicomposting Bins
When choosing a spot for your vermicomposting operation, your biggest concerns should be that 1) the ambient temperature stays between 45 and 85 degrees Fahrenheit and 2) your compost isn’t attracting animals. If done properly, you won’t even smell the compost or the food scraps (lots of people keep their operation inside the house or on the patio). Basements are a great location because temperatures don’t fluctuate much and it stays darker, which worms love.
Composting should take place in two wide, shallow, stackable bins with a lid for the top one. Because red wrigglers aren’t deep burrower like common earthworms, surface area is more valuable than depth – so think bins, not buckets. Just like with standard microbe-only composting, moisture and ventilation are important conditions for the health of both your compost and your composters (in this case, your worms). With that in mind, here are a few tips for setting up your bins:
- Wood is better than plastic for regulating moisture because it is absorbent, but it can be messier and more attractive to animals
- If you’re using plastic bins, make sure they are opaque – too much light will harm the worms
- Drill ½-inch holes in the bins for ventilation and drainage
- Put holes in the upper sides and bottom of the top bin
- Don’t put holes in the lid
- Don’t put holes anywhere in the bottom bin
The top bin is where the composting takes place and the bottom bin catches compost tea that drips down.
Vermicomposting Bedding and Feeding
Worms use bedding as both a habitat and a food source. Good worm bedding retains moisture while allowing air to pass through. If your bedding dries out, your worms will die (a not-uncommon failure for vermicomposting beginners). Good bedding materials should be loose and shredded for good ventilation, and include corrugated cardboard, newspaper, dried leaves, hay, and peat moss. Combining several of these is best. Soak the bedding in water and wring it out so it is damp but not dripping, and fill the top bin about 2/3 full with it. As you’re adding the bedding, mix in a few handfuls of dirt from your yard; this will help get microbes composting, which will help the worms digest their food better.
Red wrigglers can eat about half their weight every day, so figuring out how many worms you need starts with determining how much organic waste you produce (and intend to compost). Weigh the compostable waste you produce each day for several days, average it, and buy twice that in worms (usually sold by the pound). Simply dump the worms in the bedding-filled bin and they will work their way down under the surface to hide from the light and begin eating. It’s a good idea to let the worms adjust to their new home for a day or two before adding new compostable material regularly.
Feeding Red Wrigglers
Just like with standard microbe-only composting, there are a few rules about what you can compost. Don’t add anything non-organic, go easy on the dairy, shred or otherwise break down material before adding it, and try to add equal parts browns (for carbon) and greens (for nitrogen). Red wrigglers especially like coffee and tea grounds, eggshells (washed and broken up), rice, cornmeal, and leafy greens. When adding food, pull back the top of the worm bedding and add it underneath. There are also some things to avoid feeding your worms:
- Fats and oils (including salad with dressing)
- Eggs and meat
- Animal waste
- Acidic produce (lemons, oranges, grapefruits, limes)
- Hot peppers, garlic and onions
After 3-4 months, your vermicomposting bin’s contents will look a lot more like soil than food scraps and bedding. The soil-like material is actually nutrient-rich worm castings, and when you have that, you’re ready for vermicompost harvesting. You’ll want to extract the compost (castings) and transplant your worms to the next batch to break down, and there are two ways to do this easily:
Push everything in the top bin to one side and add damp bedding and food scraps to the other to entice the worms to leave the finished compost and migrate to the new food source. Since space is limited during the worms’ migration, you’ll need to reduce the amount of material you add at first. After a few days, scoop out the castings, replace them with more worm bedding and scraps, and return any stray worms and worm eggs (small, shiny, opaque ovals) from the castings to the bin so they can help contribute to the next round of composting.
Spread a tarp or old shower curtain outside on a sunny day and dump your compost onto it, arranging it in several piles. Worms don’t like the sun, so they’ll dig toward the center of the piles to escape it. After a few minutes you can scrape off the tops of the piles and there won’t be worms in it. Wait for them to burrow deeper and scrape again. After several rounds of this you’ll be left with little more than piles of wriggling worms that you can then return to your vermicompost bin (which you can prepare with worm bedding and new kitchen scraps between pile-scraping sessions).
Use vermicompost just like regular compost – as a supplement to garden and houseplant soil. It’s powerful stuff and a little goes a long way, so don’t overdo it on any one plant. If your vermicompost is ready before your garden is, you can store it for up to a year; just don’t let it dry out or it’ll lose most of its effectiveness. And don’t forget to empty your bottom bin once in awhile and using the compost tea you find inside.