Millions of bedding plants are produced annually in greenhouses under controlled environmental conditions for optimizing germination and plant growth.

This has become possible mainly because of the development of seedling plug production.

Photo of seedling plug production in a large greenhouse environment.

A plug is a seedling produced in a small volume of medium contained in a small cell, of which between 220 up to 800 plants are contained on a single sheet of polystyrene, Styrofoam, or other suitable material.

Plug flats are filled mechanically with a growing medium and seeds are sown mechanically into each cell.

Photo looking down on a plug flat of growing seedlings.

There are four stages of seedling development that make up plug growth.

These include:

  • radicle emergence
  • cotyledon spread
  • unfolding of three or four leaves
  • and a finished plug with more that four expanded leaves

If done correctly, plug trays can have exceptionally uniform seedlings ready for transplanting.

Photo of a plug seedling removed from tray to show emerging leaves and root system.