Growing Bearded Iris - June 4, 2014
Jeff Schalau, Agent, Agriculture & Natural Resources
University of Arizona Cooperative Extension, Yavapai County
Bearded iris (Iris germanica) is of the easiest perennials to grow in north central Arizona. This tough plant with handsome blooms is very appealing and equally rewarding. Bearded iris is also cold-hardy, drought-tolerant, requires very little maintenance, and is unpalatable to all but the hungriest wildlife. Bearded iris is so persistent that it can be seen on old, abandoned homestead sites and it was sometimes planted to help locate property corners.
Bearded iris (also called German iris) flowers have six petals; three upright petals (called standards) and three hanging petals (called falls). A fuzzy line or beard runs down the middle of each fall. Flowers come in many colors including blue, pink, purple, reddish, browns, white, yellow, and bi-colors. Most bearded irises flower in the spring (April to June depending on cultivar), but some of the new cultivars re-flower in the summer and fall. The second flower display is not as showy as the spring display but last into the fall. Many re-blooming iris are also fragrant.
Bearded iris has thick, fleshy, underground stems (called rhizomes) that store food produced by the sword-shaped, semi-evergreen leaves. The rhizomes grow best when planted at or slightly below the soil surface with feeder roots penetrating the soil below. Each year underground offsets develop from the original rhizome. Buds produce a large fan of leaves and several flower stalks. Success with iris depends on keeping the rhizomes firm and healthy. In general, this is done by providing the rhizome good drainage while the feeder roots below remain moist but not wet.
A full sun exposure is preferred; however, some of the delicate pink and blue iris maintain their color better in partial shade. However, excessive shade will reduce or prevent flowering. Good soil drainage is essential to prevent rhizomes from rotting. It may be necessary to plant the rhizomes in raised beds (at least 6 inches high) to obtain proper drainage. Iris will grow in many soil types but a light, loamy soil that has been amended with organic compost is preferred. New plantings will also benefit from a generous application of bone meal or moderate amount of triple super phosphate in the root zone (3-4 inches below the rhizome).
Bearded iris need the same good care that most flowering perennials require: deep watering in dry weather, regular weeding to reduce competition for moisture and nutrients, and fertilizing once or twice each year with 5-10-10 or similar fertilizer. Do not fertilize after mid-August, so plants have time to prepare or “harden off” before winter. After the first hard frost in fall, cut back the tops of iris plants to about six inches and clean up any remaining iris debris.
Established plants need to be divided every third or fourth year or whenever the clumps become crowded and flowering decreases. This is best done in August after flower stalks have died back. This is also the time plant new irises. When dividing, use a spading fork to lift the entire clump, being careful not to break the fat feeder roots. Wash off the soil and use a sharp, clean knife to separate the rhizomes into individual fans. Discard the bloomed-out center portions and use only the vigorous healthy fans from the outside of the clump. Cut back the leaves to about six inches and trim off any broken roots. If you wish, you can label these divisions with the cultivar name and store them for a few weeks in a cool well-ventilated place before planting, or you may plant them outdoors immediately.
We have two local chapters of the American Iris Society (AIS). These are the Verde Valley Area Iris Society and the Prescott Area Iris Society. They can be contacted through the AIS website at www.irises.org. The Prescott Area Iris Society also has its own website at: prescottirissociety.org.
Just a note about the Slide Fire: at the time this article was submitted, no lives had been lost and no structures damaged by this large fire. We are all thankful for this, but must also remember fire is an important ecological process in Northern Arizona’s forests and woodlands. Take steps to mitigate risk factors on your property and neighborhoods within the wildland urban interface. Fire will occur again and is as integral to our ecosystems as our creeks, diverse wildlife species, and climate.
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Last Updated: August 6, 2014
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