Worm castings, or vermicompost, is compost brokendown into a useable state by being munched on by earthworms. It's extreemly neutricious for you garden. Vermicompost is ready for harvesting when there is very little food or bedding material mixed in with it. The finished product should be thick, black, and relatively homogeneous. There are several methods of collecting the castings.
TIP: One week before you plan on harvesting your vermicompost stop feeding your worms. This way they will work on all of the remaining material and create a finished product.
Splitting the Bin
If you do not want to empty the composting bin, you can divide the contents by moving all the castings to one side. Do this carefully by hand while wearing thick rubber gloves. Place new bedding and food in the space you have created. Leave the bin for 2 or 3 weeks. The worms will migrate across to the side of the bin with the new bedding and food in it. The worm castings can be scooped out and the contents of the bin teased out to fill the space. Place more fresh bedding and food to build the level in the bin back up to what it was. Continue to operate the farm as usual. Very few worms will be trapped in the castings. If you are going to use the compost straight away you can pick the worms out or leave them to help in the garden.
If you don’t want to wait you can remove the castings from the bin and spread them on a large piece of polythene. Pick out the worms and return them to the worm farm. You can also remove some of the worm cocoons and replace those in the worm farm. These contain the baby worms. Use the compost or store it in plastic bags until needed.
TIP: You can go through the composter scoop by scoop and strain the scoops through a sieve. The worms and other large debris will remain and the castings will fall through. This is a quick and easy method, but hatchlings and eggs will be lost.
Emptying the bin
Place a large sheet of polythene on the ground and simply tip the contents of the worm farm out. This should be done on a bright day or under bright lights. The worms will burrow into the compost to escape the light. Gently brush the compost off the worms and they will burrow deeper. A handbrush and dust bin come in very hand for this. Keep gently brushing the compost off the worms until you have a pile of worms and a pile of compost. Move the worms into a prepared worm farm. Use the compost or store it in plastic bags in a cool dark place until it is needed. Clean out the empty bin and either set it up again or store it until it is needed again.
TIP: This process can be done incrementally, scooping out a few handfuls at a time and sorting, for more precise work. Also, if you only need a scoop or two of vermicompost to plant a container or window box, simply shine a bright light at the top of the vermicompoter. Wait twenty minutes for the worms to head deeper, and scoop off the first few inches for immediate use.
Migration to a Second Bin
Prepare a second worm farm with fresh bedding and food and place it on top of the worm farm to be harvested.
TIP: Consider placing a thick mesh screen between the two bins to keep the contents completely separate. Don't worry, the worms will migrate through the screen.
Over a few weeks, the worms will migrate from the farm that contains only compost to the more attractive fresh food and bedding in the top bin. Scoop the worm castings out of the bin. Remove any worms and replace them in the new farm bin.
TIP: This method works great, but takes the longest. Remember, don't stress about getting every last worm! Worms left in your compost will only benefit your garden in the future.
No matter which worm farming method you choose, harvesting the worm castings calls for patience. It is a job that cannot be rushed. If you want to retain some of the cocoons to keep some of the baby worms you have to pick them out carefully. They are pale, lemon shaped, and visible to the naked eye.