Sufficient water during the first three springs are important for establishing woody vegetation anywhere when dry spells sneak in after the new year. Any three weeks without rain after planting for the first three winters and springs will require watering in some form. Many locations in arid and semi-arid landscapes install large container size plants and elaborate irrigation systems. Others over-plant small container sized plants without irrigation and have at least as good a success as many using irrigation.
Large container plants require several growing seasons at the nursery and can become nursery trained or more like a horticultural plant in its development. These plants require regular watering. Small container plants are planted/seeded during the winter and out-planted the following fall after the first regular rain resulting in no nursery training.
The Pacific Northwet gets lots of water during the spring, yet can require spring watering during month-long dry spells. For those revegetation projects where no irrigation is used, a good way to ensure establishment during a growing season that is drier than desired requires some form of packaged water that is installed during the middle of the third dry week.
It is critical to ensure that larger starter plants have some form of regular watering on a two to three week schedule to ensure plants establish.