How to harvest worm castings

By Priya Agarwal


Every few months, you should go in and harvest the castings from your worm bin. This basically means separating the castings from the worms, and it can take as little as 10 minutes or as long as a day depending on the method you use. Let’s start with the quickest ways, and work our way to the most time-consuming methods.

Tray-based composting bin

This is the fastest procedure, and requires some initial investment. You need to get a tray-based vermicomposting system, which can sometimes be a little pricey. However, how these work is, you load up the trays and put your worms in the bottom tray. As they finish the food in the lowest tray, they migrate upward, leaving lovely castings behind. Once it’s empty of food and worms, all you need to do is remove the tray, empty it, and set the system back up.

Using a screen

This is simple. Just empty out the contents of the bin onto a screen or sifter, and shake till the castings make their way down onto some newspaper or a container you’ve laid out to catch them. You will probably have to make multiple passes to get all the vermicompost emptied out.

This process is quick and simple, and doesn’t require any direct worm handling. However, be careful not to shake the screen too hard, or you may hurt your squiggly friends.

The light method

harvesting vermicompost

We covered this method in detail in this blog. The benefits of using the light method are that you don’t hurt your worms, and you get vermicompost within an hour or so without putting in too much active time. You also don’t need any equipment other than a table and a strong light.

Basically, all you need to do is shine a bright light on the top surface, and as the worms burrow down to get away from the light, scrape away the top layers of vermicompost. Repeat a couple times till you can harvest no more without getting worms.

Making mounds

Dump the contents of your worm bin onto a table, and make several mounds. Shine a bright light from top. Slowly, the worms will burrow down to get away from the light, and you can scrape away the top layers of castings. Repeat several times till you’re left with just mounds of worms.

This is similar to the light method, except it requires you to handle the worms a little more.

When to harvest castings?

Earthworms can consume up to half their body weight in food per day, and they produce castings at quite a fast rate – a pound of worms can produce ten pounds of castings each month. So, if you have lots of worms, your worm bin will be getting full before you know it.

You can harvest the castings as you need them, when the bin is full, or at the start and end of the growing season. Just as long as you don’t let the bin get overly full, you should be fine.