Once spuria have finished blooming, you have two options: continue watering, but less frequently, in order to enjoy foliage longer; or stop watering completely and let the plants go dormant. Gardeners in hot-summer areas like Arizona generally follow the latter practice.
When foliage declines, cut back to 8 to 9 inches. Resume watering when new foliage emerges.
Spuria irises don't like to be disturbed and should only be divided every 5 to 10 years. Expect them to go dormant briefly after planting or transplanting. Bloom might be sparse and foliage shorter the first year, too.