This sheet insert is composed of 18 square plastic pots that are each three inches deep. The sheet is flexible, and the pots are detachable, so it should be used with a tray beneath to provide support. Start seedlings in the Professional 72 Cell Plug Trays, and pot them on into four of these 18 Cell Plug Inserts when they’ve put on a bit of growth. This size is perfect for tomatoes and peppers, but also a host of early start flowers and perennial vegetables. Any plant that might need an earlier start or a later transplant date. By potting seedlings on their roots have enough space to continue to grow and take in nutrients.