Harvesting Compost from Worm Composting Bins
by John Allen
We keep our worms in Rubbermaid bins which are about 20" by 15" by 8" deep. The bin has a few holes drilled in the bottom so that liquid can drain out. This bin is stacked on a similar bin with no holes in the bottom so that the liquid draining out the bottom of the top bin goes into the empty bin below. [I remove the worm bin and empty the liquid stored in the bin below periodically. The liquid is said to be excellent as a fertilizer for plants.] The worm bin is filled about halfway with bedding and worms and then kitchen scraps are added as available. [What worms to use and what works as bedding is available in books such as "Worms Eat My Garbage", readily available in the public library.] Over time the kitchen scraps disappear and dark brown wet compost is produced. Eventually much of the bin is full and the compost needs to be removed.
The subject of these directions is the somewhat perplexing task of separating worms from the compost that they make from your kitchen scraps. The first few times I harvested compost, I dumped the contents of the bin on a garbage bag on a table. I trained bright lights on it and harvested portions of the surface layer, meticulously picking out and saving each worm and egg case that I could find in the bedding and compost. Interesting at first, it became time consuming once we had three or four worm bins in operation. [This happens since well fed, happy worms keep reproducing. Eventually you let them reach an equilibrium with the amount of food you have available.]
The basic problem was that although the worms move away from the light source they don’t move very fast and eventually they are stopped by the surface of the table. [And you have this table of stuff sitting there during the whole process potentially grossing out your kids’ friends.] I have found an easier method for separating the compost and the worms.
The EASY way to separate worms and compost
After about four to six months of adding kitchen scraps to the worm bin, a lot of what is in the bin is dark, moist and spongy. This is the worm compost (vermicompost) and it is the goal of composting with worms. This stuff is a great fertilizer. It is a major reason for worm composting.
This method of separating the worms and the compost involves several steps. First is to empty the worm bin into some other container. As I empty the bin I set aside undigested food (for example, the banana peels that have not yet disappeared) and any masses of worms I find. I empty the rest of the nice dark, wet, spongy stuff (worms and compost) into a large container. I use an old driveway sealer container. I clean out the now empty worm bin and add some new bedding. [I use old ground leaves.] I put the undigested food and worms that I had set aside back in. I then put on top the worms and compost that had just been removed from the bin. The objective is to have the worms crawl down out of the compost and into the new bedding below (thus separating themselves from the finished compost). I leave the bin exposed to bright light (sunlight is great but indoor light works during the cold months) and wait several hours to allow the worms to migrate away from the top of the bin. I then scoop the top of the compost they leave behind into a container (another old driveway sealer container). When I start to find lots of worms as I am scooping out the compost, I wait a while for those worms to continue migrating down. I keep doing this until I am close to the top of the new bedding. I then turn everything over, shake the bin to level it, add some new food scraps, cover the surface with a piece of black plastic and I am done harvesting the vermicompost. I put the top back on the bin but offset an inch or two. [Otherwise, in total darkness the worms crawl all over the top of the bin and some fall out when you open it to add new food scraps.] I now have most of the worms in the worm bin with new food and bedding and much of the compost in a container ready to be taken out to the garden and used.
I don't have any qualms about getting worms on my hands in this process. One reader wrote: "I put a 1/4" screen over the top of the new bin (fit right inside in contact with the bedding below). Then I dump, (wait for the worms to migrate down), lift the screen out, dump castings and do it all over again." This method probably requires putting part of the worms and compost from the driveway sealer container in at a time. But it reduces contact with the worms if that is a concern.
If you have questions about this method, email me using the email address found on the home page.
