Ideal for seed starting. Keeps varieties separate and facilitates removal of seedlings for transplanting to larger containers such as Pro Trays. All are standard size (11" by 21") and include drainage holes. Trays and flats are made of 80% recycled scrap polystyrene and are reusable and recyclable. Compatibility: Use with Shallow Germination Trays (black) or Shallow Leakproof Trays (white) only.