Abstract: Control valves are known which incorporate moisture sensitive material to control the flow of fluid through the valve. Described herein is control valve (1) which incorporates a moisture sensitive material (4) in contact with and responsive to increasing environment moisture levels. The material (4) acts on a moisture impermeable flexible film (5) to shut off a fluid flow connection between an inlet (6) and an outlet (7), the material (4) being sealed from the inlet (6) and outlet (7) by the film (5). Also the invention provides a method of plant growing in which method one or more plants are grown in a growing medium comprising hydrogel particles charge with aqueous nutrient solution for the plant or plants, the growing medium being housed in a substantially water-impermeable container and the plants extending out of container, and, when the water content within the hydrogel particles falls below a predetermined level, introducing further nutrient solution into the container.