Harvesting Your Worm Castings

It’s Time to Get Sifty!

Freshly sifted worm castings.

It’s been a year, or maybe even less, since you’ve started your worm farm. You notice your population starting to increase, the amount of food they’re eating has started to grow, and the bins are feeling pretty heavy when you’re checking on them. You can see the worm castings that are taking over their homes. It's time for you to harvest! 

Since the worm castings have a lot of living microbes and good bacteria that plants love, it’s best to wait and harvest until you know you’re going to use it. If you have multiple worm farms, it may be best to harvest one farm when you’re getting ready to start seeds, since vermicompost makes a great addition to a seed starting mix while saving the other farms to use for top dressing or soil mixture later in the season.

The vermicompost may be pretty wet when you want to harvest, so it helps to stop feeding about two weeks to a month before you’re ready. Make sure you add in some extra bedding as well to help absorb the excess moisture. Technically though, you don't even have to sift your harvested castings. It's an extra process that we do here at Sevans Wormery because we love how the end result looks and feels. If you want to save yourself some time and energy, you can pull castings out of your worm farms as needed and add it right onto your plants or into your soil. You'll more than likely bring some worm friends along with you, though! 

Mining for Your Black Gold

Now that your farms are ready to harvest, you want to make sure you have everything you need. There are tons of different ways to sift your castings out, and you may find that our ways don’t necessarily work best for you, and that’s alright! You can hand sift, you can use an electric sifter, some people are even crafty enough to make a hand-cranked sifter. We used a hand sifter for five years before finally switching over to our electric Brockwood Worm Shifter in 2025.

No matter what sifting method you choose to use, you'll always want to let your castings dry before sending them through. Wet castings will clog the screen and make a mess. You want it damp enough that it can hold a shape, but it will easily fall apart when touched. We lay our castings out on a tarp to dry for at least a week before sifting and add some food for any straggler worms. The tarp is helpful for cleanup, and it allows us to pull our castings to dry in the sun if it's a nice day outside. We have a dehumidifier we can use, but usually we let our worm castings dry out naturally. This way the worms that are stuck in the castings have a longer chance to make it to the food pile.

Back when we were hand sifting, we had two different screens we ran our castings through. The first was a 1/4-inch screen to get out any large clumps of bedding and unprocessed materials. Anything left behind got set aside and used in a restarted farm. Next, anything that fell through the first screen got sent through our second sifter which had an 1/8-inch screen. This sift is what gets our castings into that fine, soil-like consistency we're looking for. 

Now that we're using an electric sifter, our process is mostly the same, only the sifter is doing all the hard work instead of our hands. It has a slight slope design, so all the castings start at the top where the finer screen is, and as it works its way down, the screen size changes so the worms and cocoons get separated out, and then remaining unsifted items falls off the end. If the castings are a little wet, we'll run it through again after a few days. 

If you can't get everything out, don't worry! Having castings in a newly started or restarted bin is a positive. It gives the farm a boost and starts it off with that diverse microbiology you're looking for. 

Our first-round sifter is on the bottom and our fine sifter is on top.

To make your own sifter, all you need are some 2x4s, some screws, a fine, mesh screen (we used an 1/8-inch screen) and a 1/4-inch screen if you want to make both kinds of sifters. The sifters work best if you have longer side boards that act as a handle, and it’s definitely easier to do with a partner. We find that sifting over a wheel barrel works best for us, so we made a sifter that fits over that. As long as you’re able to separate out your bedding from the vermicompost, it doesn’t really matter how you do it. Luckily the worms are very easy going!