This large unheated propagator with no drainage holes is perfect for filling with smaller trays or pots or multi cell inserts. The clear cover with an adjustable dial vents allows you to control the temperature and humidity within the Humidity Dome. The large area of the Humidity Dome allows you to grow a multitude of different species, and once established can be potted or planted in your garden. Most seeds, require moisture and warm temperatures to germinate. Essentially an inexpensive plastic cover, a humidity dome, helps maintain ideal humidity and temperature levels in the tray to maximize seed germination. Applying heat to the bottom of a flat as the seeds germinate will increase your success and ensure a healthy root system. Should you wish to add heat, you can purchase a heating pad.