The cells of the Rootrainer seed starter kit are hinged at the bottom, opening like a book for easy root inspection or transplanting. Roots are automatically air-pruned to create a denser root mass, and grooved sidewalls direct them straight down to minimize spiraling. Seedlings slide out easily, avoiding damage to the root system and associated transplant shock. Similar to seed starters used in commercial nurseries, its cells are 5" deep by 1 1/2" square. Each kit consists of a frame and eight four-cell books, for a total of 32 growing cells. Made from reusable polystyrene. Instructions included.