Description from Johnny Selected Seeds
Designed for fresh market growers. Square cells.
Rigid design allows use without a bottom tray, allowing more plants to fit in your greenhouse. 50-cell flats are recommended for tomatoes, melons, squash, cucumbers, and for growing larger flowers, herbs, and other vegetables. With drainage holes. Compatibility: Use with Shallow Germination Trays (black) or Shallow Leakproof Trays (white) only.