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Program Resource

Vermicomposting

Vermicomposting is a word used to describe composting using worms. This method is pretty small-scale, so it should be used alongside other more large-scale composting methods. It is a great way to get kids aware and thinking about decomposition, and unlike other methods can be done inside the classroom. The finished product, worm castings, is even more nutrient-rich than regular compost!

How to Set Up a Vermicomposter: 

* Figure out how much food waste you produce in your kitchen that worms can eat. Acceptable food scraps to add to a worm bin are provided in this list, as well as considerations and foods to avoid. 

  1. Build a worm bin. Instructions to build your own are here. If you want to buy one, it will be more expensive, but you can find a good one here. In general, you want a shallow bin with large surface area that is made of solid material, but you also want to keep the light out and moisture in. A good rule of thumb for how big your bin should be is 1 pound of worms (about 1,000 worms) per square foot of bin surface area. If your bin is .5 ft wide and 2 ft long, you would buy 1 pound of worms. You will always need a tray below the worm bin to catch drainage and fallen compost. You also need a cover for it to keep out light and keep in moisture. 
  2. Pick a location for your bin. Worms like temperatures between 55 – 77 °F. In winter, you should choose a heated kitchen, basement, or garage to prevent worms from freezing. In summer or warmer months, you may move it outside, but you should never store your worm bin in direct sunlight, only in shaded areas. 
  3. Add moistened, shredded bedding (black ink newspaper, corrugated cardboard, partially decomposed leaves, egg cartons, finished compost, or a mixture of any of these. A more complete list is here. You want your bedding to take up one-third to one-half of your worm bin. Add water to it before you add it to the bin, aiming for the bedding to be about as moist as a wrung-out sponge. Worms need this water to be able to breathe! You can also add eggshells that will control the acidity, and a small amount of soil, sand or cornstarch. Whatever you add should be non-toxic, since worms will be eating all of it.
  4. Get your worms for your worm bin. Red wigglers or manure worms are the two types of worms that are surface feeders and will be appropriate. Make sure you get one of these types, otherwise your vermicomposting will not work! The rule of thumb is to have one pound of worms for every pound of food waste you produce daily.
  5. When your bin and bedding is all ready, make a shallow depression in it. Add your worms to the bin first. Don’t add food waste yet! Also, at this point you will keep the lid off or askew to encourage worms to burrow down into the bedding away from the light. After about a week, the worms will get used to their new environment and you can add food scraps. 
  6. Once the worms have acclimated, start adding food scraps by burying them into the bedding. You will want to feed them only about once a week, but you should check every now and then to see if you need to adjust for your worms. Give them only amounts of food you know they can eat, so your worm bin doesn’t begin to smell due to undigested food scraps. 
  7. After about three months (the general range is 2.5 months to 6 months), your vermicompost should be ready to harvest, depending on how many worms you have and how much you have been feeding them. If you want your worm bin to keep going into the next seasons, you will need to remove the worm castings and replace the bedding. Here is a guide that can take you through different ways of removing the castings. You can put the finished worm castings on your garden for particularly resource-intensive plants, or mix it in with your regular compost. 

Troubleshooting: 

  1. Your worms are trying to escape. This generally means one of four things: a) that your bin is too full of castings; b) that your bin is not draining well enough and is too wet; c) that your bin is too dry; or d) that your bin is too acidic. If the problem is too many castings, you can harvest them. If that doesn’t fix the problem, check your moisture levels. Here is a guide to checking whether moisture levels are right for your worm bin. If you are still seeing worms trying to escape your worm bin, it might be the acidity levels. Here is a guide to address excess acidity or alkalinity (not enough acid) in your worm bin.   
  2. Your worm bin smells bad. In most cases, this means the worms are being fed too much food. The smells will be coming from undigested food waste, not from anything else. Make sure when you add food that you are burying it deep enough in the worm bin. Here is a guide to addressing bad smells coming from your worm bin. 
  3. Your worm bin is attracting fruit flies and gnats. Again, this is probably due to too much undigested food in the bin. However, dealing with fruit flies can get tricky. This guide can help you both get rid of them and prevent them from coming back to your worm bin. 
  4. Your worm bin is molding. This is not actually a huge problem for the worms, but if you are concerned about the mold for your own health reasons, check out this guide to reduce mold in your bin. Mold can also occur when your worm bin is too acidic, so adding eggshells and reducing how much citrus fruit you add should help.