PlantLife Online

Answer

The recommendation "water thoroughly and to let the plants dry well in between waterings" is commonly used in the trade because all soils are different and have a different water holding capacity. The soils in Phoenix are generally very course and has very little organic mater to hold water therefor percolates very quickly, unless they have been generously amended. For your situation I would recommend watering the new plants twice a week during the hottest summer months and once a week or every other the remainder of the year. Each time you water it should be enough to fully saturate the soil and penetrate the root zone, deep watering for the first year or until the plants have established will encourage healthy root development. Once established the watering should scaled back overtime.

These are just genneral recommendations if you really want to be sure the soil has dried throughly before watering you will need to use a soil probe or dig down near the rootball with a spade or narrow shovel to actually feel and see the moisture content (This only needs to be done a couple times not before each wtaering). This will give you a good understading about your particular soil and its abilty to hold water. Once you have an understanding for your soil type you can use the same water schedule for all new plantings in your landscape. 

Hope this helps!

PlantLifeOnline