The present invention provides systems and methods in which a microprocessor (220) is programmed to calculate an accumulated watering need for an irrigation zone of station (400)and control irrigation to the zone or station (400) using an automatically varied cycle amount that falls between a user controllable maximum threshold and a user controllable minimum threshold. The cycle amount is preferably at least partly derived from ETo data. The minimum threshold may vary during a period of 12 consecutive months, may vary as a function of time of year, as a function of crop maturity or as a function of any other suitable factor where it would be advantageous to set a minimum threshold. The cycle amount may equal the accumulated ETo value(s) or may equal the maximum threshold value. Furthermore, the microprocessor (220) may be programmed to control the irrigation to the zone or station (400) using an automatically varied day schedule.