Use with Jumbo Plug Flats and Pro-Tray Cell Flats to contain water drainage and for bottom-watering applications. All are standard size. 11" by 21". Trays and flats are made of 80% recycled scrap polystyrene and are reusable and recyclable. Compatibility: Use with Pro-Trays, Jumbo Plug Flats, Soil Block Propagation Trays,and Mini Square Plastic Pots.