Abstract: A novel greenhouse curtain system has a plurality of movable curtains oriented vertically one above the other to form a flexible wall. Each curtain is supported by a fixed upper edge, and the vertical position of the lower extent of each curtain may be adjusted by means of a traveling spindle used to furl or unfurl the curtain. The traveling spindle rises and descends as the curtain is furled (raised) or unfurled (lowered), and is rotated by a tensioned cable wrapped in opposite directions around two drums aligned concentrically one on end of the roller bar. The cable is anchored on one end below one of the drums, and is wrapped in opposite manner respectively around both drums and passes vertically to a pulley, and then to a driving means such as a winch. The dimensions of the drums are such that the curtain remains in stable position as long as there is no movement of the cable to or from the driving means.