Irrigation scheduling is the process used by irrigation system managers to determine the correct frequency and duration of watering.

The following factors may be taken into consideration:

• Precipitation rate of the irrigation equipment
• Soil infiltration rate
• Soil available water holding capacity
• Effective rooting depth of the plants to be watered
• Current watering requirements of the plant (which may be estimated by calculating evapotranspiration, or ET)
• Amount of time in which water or labor may be available for irrigation
• Amount of allowable stress which may be placed on the plant. For high value vegetable crops, this may mean no allowable stress, while for a lawn some stress would be allowable, since the goal would not be to maximize production.
• Timing to take advantage of projected rainfall
• Timing to take advantage of favorable utility rates
• Timing to avoid interfering with other activities such as just before a sporting event or just prior to harvesting a crop

The goal in irrigation scheduling is to apply enough water to fully wet the plant's root zone while minimizing overwatering and then allow the soil to dry out in between waterings, to allow air to enter the soil, but not so much that the plant is stressed beyond what is allowable.

In recent years, more sophisticated irrigation controllers have been developed that receive ET input from either a single on-site weather station or from a network of stations and automatically adjust the irrigation schedule accordingly. When properly set up and maintained, these controllers do tend to conserve water over conventional human scheduling as the program is updated at least daily.

Other devices helpful in irrigation scheduling are rain sensors, which automatically shut off an irrigation system when it rains, and soil moisture sensing devices such as tensiometers and gypsum blocks .