Harvesting from a vermicompost bin is the process of separating the worms from the finished product, known as worm castings or vermicompost. Vermicompost is a nutrient-dense soil amendment created from the digestion of organic waste by composting worms, typically red wigglers (Eisenia fetida). The goal is to collect the valuable castings for use in gardening and to preserve the worm population to continue the composting cycle. Harvesting becomes necessary when the majority of the bedding material has been converted into the dark, crumbly finished product.
Preparing the Vermicompost Bin for Harvest
The optimal time for a first harvest is typically three to six months after the bin was established, once the material is mostly uniform and dark. Before harvesting, preparatory steps ensure a cleaner, more efficient process. The most crucial step is to cease feeding the worms for about seven to ten days prior to the harvest date. This period allows the worms to process remaining food scraps and clear their digestive tracts, resulting in higher quality castings.
Managing the moisture level is also important to prevent the castings from clumping or becoming a dense “vermi-concrete.” If the bin material feels overly wet, spread it out in a shallow container for a few days to allow surface drying. The ideal consistency for harvesting is slightly drier than a damp sponge, which encourages the worms to move more easily during separation.
The Light Migration Harvesting Method
The light migration method is a popular, non-mechanical technique that utilizes the worms’ natural aversion to light. The process begins by emptying the entire contents of the bin onto a flat surface, such as a tarp or plastic sheet, under a bright light source. The material is then shaped into several cone-like piles, approximately six to eight inches high.
The bright light causes the worms at the surface to immediately burrow deeper into the pile’s center. After waiting about 15 to 20 minutes, the top one or two inches of the worm-free castings can be gently scraped away and set aside. This action exposes the next layer of worms, prompting them to burrow even deeper into the shrinking pile.
This scraping and waiting process is repeated three to four times over an hour or two. Eventually, the majority of the finished castings will have been removed, leaving behind a small, dense mass of concentrated worms at the base of the pile. This method collects the worms for transfer to a new bin while separating the bulk of the castings.
Sifting and Screening Techniques
Sifting and screening offer a more mechanical and precise approach to separating worms. This technique involves passing the bin material through mesh screens, which separate the particles based on size. This process is effective for isolating the finished castings from larger material like undigested scraps and bedding.
A coarse screen, often with a 1/4-inch mesh, is typically used first to remove large debris and chunky material, known as “overs,” which can be returned to the worm bin. The material that passes through can then be run over a finer screen, such as a 1/8-inch mesh, to separate the worms and their cocoons from the fine castings. Smaller mesh sizes, down to 1/12-inch, produce the cleanest vermicompost but take longer to process.
Screening is generally more effective when the material is slightly drier, as excess moisture can cause the castings to stick and clog the mesh. Any worms or cocoons remaining in the overs can be manually picked out or returned to the new bin to continue the cycle.
Post-Harvest Handling of Worms and Castings
Once the worms are separated, they require immediate attention to ensure their survival. The concentrated worm mass should be quickly transferred into a newly prepared bin containing fresh bedding and a small amount of food. This re-bedding process prevents the worms from becoming stressed or dying from a lack of resources.
The harvested castings can be used immediately or stored for later application. For storage, the vermicompost should be placed in a non-airtight container and kept in a cool, dark location. It is important to maintain some moisture in the stored castings to preserve the beneficial microbial life, which are responsible for the product’s soil-enhancing qualities. The harvested vermicompost is then ready to be applied directly to plants, mixed into potting soil, or used to create nutrient-rich liquid fertilizers.