Plug Trays were originally used in commercial horticulture and are now common amongst home gardeners. The purpose of the Plug Tray is to provide a single plant with its' own cell of compost. This allows a plants roots to grow undisturbed by its' neighbours resulting in stronger plants. Plug Trays make it easy for you to take plant from tray to pot without any root disturbance - resulting in uniform growth. Your plants are ready to pot up from plug trays when they have three or four leaves. Gently pushing each cell from below will allow you to easily remove the plants. Plug Trays are good for growing annuals, where root damage when planting out can lead to a check on growth from which the plant never recovers.