What is The Worm Factory® 4-Tray Recycled Plastic Worm Composter - Green and how does it work? This green 4-tray worm composter is a multi-tray compost system that helps manage the composting process and provides you with nutrient-rich compost for your garden. It's easy to set up and simple to use. Fill each stacking tray with kitchen scraps such as newspaper, junk mail, vegetables, fruits, egg shells, coffee grounds, paper, and cardboard into nutrient-rich compost for your garden. Most "Master Gardeners" consider worm castings to be the very best compost available. Your plants will thrive with this all-natural compost. Sorting out the undigested scraps can be a messy, inconvenient chore with ordinary worm composters. Worms start in the bottom tray and migrate upward as they break down the waste