Abstract: An automatic irrigation control includes a pilot needle valve with a slidable stem and a block of material the dimensions of which change when exposed to moisture, arranged in a framework so that when the block expands it bears against the valve stem, closing the valve and shutting off a connected hydraulic valve. Preferably, an override lever, connected to a temperature-responsive device, is interposed between the block and the valve in such a way that when the temperature is above a predetermined height, the lever overrides the block and prevents the actuation of the hydraulic valve when the temperature is too high. An adjustable canopy regulates the rate of drying and wetting of the block.