Abstract: An irrigation controller contains a base unit having drivers and output switches for controlling a number of irrigation stations which is less than the maximum number of stations for which the controller is designed. Station expansion modules are provided having the drivers and output switches for incremental numbers of stations. The station expansion modules can be individually bought and connected to the base unit to expand the number of available irrigation stations up to the maximum number of stations. A microprocessor in the base unit can be programmed and controls all of the stations, both those in the base unit and those in the station expansion modules. Pump and accessory timer modules can also be provided for optionally driving a pump and/or an accessory device such as a lighting system.