Made of naturally composted materials, each Ready-Gro plug contains beneficial fungi and may be inoculated with other biological controls. It is an optimally-aerated medium that naturally maintains the proper air/water ratio to promote healthy growth. Fits Rapid Rooter tray cells and other plug-and-grow trays. Ready-Gro plugs are an ideal way to snugly start seedlings and cuttings. You simply nudge the plant into the soft and secure surrounding media, which hold it tightly. After you water the plugs, they expand slightly, giving plants a firm place to take root. The plugs are also easy to remove from their cells for transplanting, so you'll avoid worry and heartache over broken or damaged roots and stems.