two girls in a greenhouse harvesting worm castings

Using the light method to harvest worm castings

earthworms in hand

Harvesting worm castings from your worm bin can be a messy endeavor, especially if you don’t use the correct method. You’ll want to get things done quickly, so your worms can go back to being their hungry, productive selves, and so you have to deal with worms for a shorter period of time. After all, even though they’re your “pets”, nobody’s especially fond of handling worms.

In this blog, we want to go over the light method of harvesting vermicompost. How to prepare, necessary supplies, and finally the method itself.

Getting the worm bin ready

Before you harvest, you need to do a couple things. First, stop feeding the worms for a couple days. This is done so all (or nearly all) the food and bedding is gone by the time you’re ready to harvest, so your castings aren’t contaminated with pieces of worm food.

Check the worm bin everyday to see if the food has gone. When the bin looks like its contents are 95-99% castings, it is ready for harvesting. Worm castings look like crumbly chocolate cake without the icing (but they sure don’t taste like it).

It’s a good idea to harvest your worm castings often, because that keeps the bin more manageable, and your worms will appreciate having their bedding changed.

What you’ll need

It’s a good idea to have your tools on hand before you start the process, so you don’t have to run out to gather things while you’re working. Let’s work our way through the materials you’re going to need to use the light method of composting.

  • A table or working surface
  • A strong light
  • A container for the castings

…and that’s it! You usually expect something like this to be super complicated, but it really isn’t. Now you’re ready to move onto the next section, which is…

Using the light method

The light method is a simple yet effective method of harvesting worm castings, and it works like this:

  • open worm bin
    Open the bin, remove any loose bedding or food, and place the open bin under a strong light
  • Worms prefer to be in the dark, so they will burrow deeper to escape the light
  • As the worms dig down, scrape away the top layer of compost, and expose the next couple inches to the light
  • Keep doing this till you’re almost at the bottom. Stop when you reach worms and give them some time to move further down. Once you cannot harvest any more vermicompost, lay down some fresh bedding, mix it in, and give your worms some food.

You should be done with harvesting and putting down fresh bedding within 30 minutes. You can then screen the castings to make sure all material is completely composted, but if you’re harvesting them for use in your garden, they should be just fine.

Other methods

Some other methods include the food migration method, screening, and the water harvest method. These are all simple and effective, but if you’re new to vermicomposting, we recommend the light method as one of the simplest. It is very beginner friendly, you won’t have to handle the worms much, and you don’t need too many tools or a setup.