During plug production, seed germination and seedling emergence is extremely important. The objective is to get as close to 100% emergence as possible. Some growers elect to germinate plugs in controlled germination rooms. There are a number of different designs, but all control light, temperature and humidity in the rooms.
Large growers build large rooms to accommodate the large number of plug trays they produce each spring. They may roll the trays into the growth room on trolleys or they can be transferred to lighted racks.
The most sophisticated germination rooms have the insulated side walls and the ability to fog the room to maintain high relative humidity.