An irrigation controller includes a base unit with a removable and programmable control panel and backplane circuitry for communicating with a plurality of removable modules capable of performing a variety of irrigation and non-irrigation functions. A base module having irrigation station drivers is mated with the backplane circuitry and communicates with the base unit to carry out basic irrigation functions. A plurality of expansion modules and one or more smart modules, each having its own logic circuit, can be mated with the backplane circuitry to communicate with the base unit and carry out additional irrigation and non-irrigation functions.