How to build a worm composting bin inside or outside the home
Q: I live in an apartment and would like to compost using worms. Can you tell me more about how to get started?
A: Composting using worms is called vermicomposting. This type of composting uses worms to recycle food scraps and other organic materials into a much sought-after soil amendment called vermicompost, or worm castings. Vermicomposting can be done almost anywhere and is easy to do. Our Master Gardener group has sponsored a worm composting project in North State elementary school classrooms for several years. Master Gardeners provide the worms and worm bin to a classroom that adopts and cares for the worms during the year, composting the food scraps generated from the students in the class.
To get started, we recommend using two to 10 gallon, or larger, plastic storage tubs with one lid. Drill about 50 quarter-inch holes in the bottom of one of the tubs. Place a brick, or block of wood in the bottom of the container without the holes. Next, stack the tub with the holes inside the other tub so it sits on top of the brick. Stacking one storage tub inside the other, allows for the “worm juice” to be collected in the lower bin and keeps the worms from getting too wet. The liquid collected can be used to fertilize plants.
Next, add three or more inches of bedding to the tub with the holes. The bedding can be shredded newspaper, cardboard or brown bags; coco coir or leached peat moss. Don’t use glossy or white paper, as these have chemicals that are harmful to worms. Make sure the bedding is fluffy and moist before you add the worms. We like to start with newspaper strips that have been separated and sprayed with a spray bottle so that it has the feel of a wrung out sponge. Make sure to have additional moist material to use to cover the worms and the food you place in the tub. If the bedding is not kept moist the worms will dry out.
For a standard size worm compost, start with a pound of red wiggler worms, Eisenia foetida. These are adapted to living in the top six inches of soil in the organic layer, unlike night crawlers that like to burrow deeper into the soil. Worms can be fed vegetable and fruit scraps, grains, beans and bread, egg shells, fallen leaves, coffee grounds, lawn clippings, coffee filters and tea bags. Avoid citrus fruits as they are too acidic for worms. Also avoid meat, dairy and oily foods; these can create a very bad smell in the tub.
Once you have the worms placed in the bin with food, place the lid on top of the tub. Make sure to drill a few holes in the lid to allow the worms oxygen. I like to add a lightweight plastic screen under the lid to keep the worms from crawling out, but this should not be necessary if your worms are kept well feed.
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Worms should be fed every few days. Make sure that bedding stays moist but not soggy. Worms have a gizzard, similar to birds, that helps them grind their food. Adding ground-up eggshells, oyster shell flour or a handful of gritty soil to your bin will help your worms process food better. Make sure to keep the worms bin out of direct sunlight and protect from freezing. When you get ready to harvest your worm casting, feed the worms on one side of the tub until they all collect on that side, and then harvest vermicompost from the side of the tub without the food.
For more detailed information on vermicomposting, check out the “The Worm Guide: A Vermicomposting Guide for Teachers” at bit.ly/3cGt6DI.
The Shasta Master Gardeners Program can be reached by phone at 530-242-2219 or email firstname.lastname@example.org. The gardener office is staffed by volunteers trained by the University of California to answer gardeners' questions using information based on scientific research.