Abstract: Apparatus for heating the soil or other growth media in a plant propagation container, including a set of low-voltage silicone-encased heating elements embedded directly in the growth media. The silicone heating elements are sturdy and inherently waterproof, as they are designed to operate in harsh, high moisture industrial environments, and placing them in the growth media itself dramatically improves the heating efficiency and effectiveness. And being low voltage devices, typically 12 VDC, the risk of electrical shock to workers is substantially eliminated, even should the electrical cords become damaged by abrasion or misuse. Preferably, the apparatus includes a set of heating elements, a DC power supply for developing the DC operating voltage for the heating elements, and a thermostat for regulating the amount of heat produced by the heating elements.