How to grow spuria irises
Choose a planting site in full sun and amend the soil with plenty of compost or other organic matter. If soil is acidic, also add lime.
Get rhizomes into the ground immediately; they can't tolerate drying out. Plant 1 inch deep in heavy soil, 2 inches deep in sandy soil. Space rhizomes at least 2 feet apart. Keep them well watered from planting through bloom period.
You'll get more blooms if you feed spuria consistently. One strategy: apply a balanced, controlled-release fertilizer in early spring and again in early autumn.
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.