Iris – for a rainbow of color

Local gardens are now awash in all hues of the rainbow and vibrant iris are at their peak. Iris is one of the easiest hardy perennial plants to grow. With so many colors and types of iris available for home gardens, everyone should have favorite.

Tall bearded German iris typically bloom late May and last but a few short weeks each year. This well-known plant was one most likely grown in your grandma’s flower garden. More recent cultivars have larger flowers than the type grandma grew. Beverly Sills, Bride’s Halo and Batik are just a few popular choices for central Iowa gardens. Locate beds in a full sun location for best bloom.

Some tall bearded irises, such as Immortality, are called rebloomers that may bloom again later in the season. However, the reblooming tendency is not reliable and can vary, depending on weather conditions and cultural practices. Keep plants well-watered and apply fertilizer during the summer months to encourage rebloom.

Apply a light application of 10-10-10 fertilizer in early spring and a second light application a month after blooming. Avoid high nitrogen fertilizers, which can cause rot. Do not fertilize after mid-August, to allow plants time to prepare or “harden off” before winter.

If your iris are becoming crowded or producing less flowers, it is time to divide them. Dividing established iris beds every three or four years will help keep your plants healthy. The best time to divide and plant iris is mid-July and August. This gives plants ample time to become established before winter sets in.

Did you know? Iris rhizomes are actually fleshy underground stems. Once an iris rhizome has bloomed, it will not bloom again. New iris rhizome segments develop, extending out from the old mother rhizome, that produce the flower buds for next year’s bloom. Reblooming iris can complete this growth cycle in a single season, allowing them to bloom again, a condition called remontancy.

For further information on growing iris or other gardening questions, contact Yvonne McCormick at yvonne@iastate.eduvvvvvvvv