Cool Season Turf
Cool-season grasses are grass types that thrive in areas with cold freezing winters and hot summers. This area is roughly defined as New England, the Upper Midwest, Intermountain West, the High Plains, and Northern California up to the Pacific Northwest. These grasses grow best when temperatures are between 65-80 degrees F, which is why they do most of their growing in the spring and fall. The major grasses in this category are Kentucky bluegrass, perennial ryegrass, tall fescue, and fine fescue. Typical effective Root Zone Depth at maturity is 6 to 8 inches. Manual watering may be advisable when growing from seed or sod until the root zone develops. Source: http://www.scotts.com
Warm Season Turf
Warm-season grasses are originally from tropical regions, which is why they thrive in the scorching sun and high temperatures of the Southern US. Warm-season grasses grow best when temperatures are between 75-90°F and do most of their growing in the summer. In the cooler weather of late-fall and winter, they go dormant, turn brown, and won’t green up again until warmer weather returns in spring. The major grasses in this category are bahiagrass, bermudagrass, centipedegrass, St. Augustinegrass, and zoysiagrass. Typical effective Root Zone Depth at maturity is 8 to 12 inches. Manual watering may be advisable when growing from seed or sod until the root zone develops.
Annuals start out from seed each year and typically are not able to overwinter in cold climates. Typical effective Root Zone Depth at maturity is 4 to 6 inches. The shallow root system of annuals generally requires more frequent watering than other plant types in order to keep the soil reservoir moist.
Trees generally have the most extensive root zones, with typical effective Root Zone Depth at maturity of 12-24 inches. The deeper and broader root system of trees means that the interval between watering may be longer than for other plants. Since trees are often in mixed zones with turf, annuals, or shrubs/perennials, it typically makes sense to schedule a zone according to the plants which have shallow root zones so that they get sufficient water.
Shrubs & Perennials
Shrubs and perennials are able to overwinter in climates to which they are suited. In cold climates they may lose leaves and/or upper portions of the plant may die, but the root system persists and the plant will continue to grow year after year. In warm climates they may retain their leaves or foliage year-round. Typical effective Root Zone Depth at maturity is 6 to 12 inches.
The key characteristic of desert plants is their low water usage which makes them adaptable to arid climates. Desert plants are common in the Southwest and Intermountain West. Root zone depths vary greatly among different types of desert plants; however, for scheduling purposes it is generally advisable to use an effective Root Zone Depth at maturity of 6 to 12 inches. During cool and monsoon seasons it may be possible for desert plants to go weeks in between watering. During the hottest, driest months the watering interval is typically shorter due to higher evapotranspiration.