Heavy Duty Reusable 4-Cell Plug Tray Inserts. These heavy-duty seed starting tray inserts are the perfect upgrade for your seed starting setup. Guaranteed to last multiple years, they are large enough to start any plant from seed in preparation for garden or container transplanting. We recommend using them for seeds that are started indoors over a period of several weeks, but will put on a lot of root growth, such as tomatoes and peppers. It is easy to see and feel the quality of these trays from the moment you unbox them, and their utility only increases as you use them to start seeds or pot-up seedlings.