Once the worm bin has filled with several inches or more of dark worm castings and no visible food remains, it's time to harvest the compost.
Compost in a plastic bin, especially if it is deep, will need to be turned. The bottom layer usually lacks oxygen. Turning it allows the bottom to get air and finish composting.
Separating worms from compost can be a very tedious affair. One prescribed way to separate worms from compost is to feed one corner of the bin only and have the worms migrate to that corner. Unfortunately, this method is very slow.
Another method is the light harvesting method. This method involves shining a light on top of the compost, forcing the worms down. The compost is then skimmed off the top until only a layer of worms remain. This method can be very time consuming, especially if there is a lot of compost to separate.
Harvesting Worm Compost Using a Tub
One of the easier ways to harvest worms is to use a plastic tub with large holes drilled into the bottom. Place the compost with worms inside the tub with holes. Place that tub on top of a new container full of fresh bedding and food for the worms. This requires that the tub with holes fit inside or on top of the new container.
The worms will naturally want to move away from their castings and to a new food source. A light can be shined over the top of the compost to encourage worm movement. A plastic garbage bag with holes poked in it can be substituted for a plastic tub.
Harvesting Worms Using a Potato Bag or Sock
This method uses the same concept of having the worms move themselves. This time, the worms will move to a smaller container within the original bin of compost. Fill a plastic potato bag, which has air holes, with worm food. A sock with holes cut in it can be used as well. Place the bag or sock on top of the compost with worms.
The worms will move into the bag or sock, which can then be dumped into the new worm bin. Repeat the process until all the worms are harvested.
Screening Worm Compost Using Wire Mesh
Commercial worm farms use large machines which shake or tumble worms and compost apart. Home vermicomposters can employ this method of separation. The compost needs to be fairly dry before it can be screened. Use 1/4 inch or 1/8 inch hardware cloth. Gently push or shake the compost through the screen.
The larger, 1/4 inch screen will yield a coarser compost. The smaller, 1/8 in screen will yield the finer worm castings. Uncomposted food and bedding plus the worms can be returned to the bin.
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