Finished worm castings can be harvested in three to six months. There are several methods of harvesting. One convenient way is to move the finished compost (worm castings) to one side of the box and add new dampened bedding to the other. Feed only the new side. Place a black plastic sheet over the new bedding and expose the finished side to light and air. This allows the completed compost side to dry and encourages the worms to migrate to the side with fresh food. After about a month, most of the worms have transferred and you may remove the castings to use in plant mixtures. Add fresh bedding to the vacant spot and begin feeding again.
Another process that works well with kids is harvesting compost by the “dump and sort” method. Dump the contents, worms and all, on a surface. Divide the castings into several cone shaped piles. Wait ten minutes and start pulling the castings away from each pile. This will cause the worms to retreat to the center to avoid light. Repeating this process will result in a ring of castings surrounded by a pile of worms, which can be returned to the bin along with new bedding to begin the process all over again.