Abstract: This invention relates to an improvement in the ventilation of a greenhouse and it consists of an elongated tubular inflatable member mounted to underlie an air vent extending along the ridge portion of the greenhouse and a second vent consisting of an elongated opening in the side wall of the greenhouse, each of the vents having an inflatable tubular member carried adjacent thereto whereby the inflatable members in deflatable condition permit the circulation of outside air from the side vent through the ridge vent and an air pump having a line running to each of the inflatable members inflating the same to seal the vents.