A snow melting system for greenhouse comprises sensors for measuring an accumulation of snow on or at the greenhouse. A snow melting processor unit comprises an accumulation rate calculator for calculating an accumulation rate of the snow from the measured accumulation, and a heating prioritizer for actuating at least one of at least two different heating systems of the greenhouse as a function of at least the accumulation rate. A rooftop greenhouse system comprises a greenhouse adapted to be mounted to a rooftop surface. Two or more different heating systems mounted to the greenhouse to heat a roof of the greenhouse, and controlled by the snow melting system.