Helping Nebraskans enhance their lives through research-based education.
Create Color Throughout the Summer with Iris
submitted by Sarah Browning, UNL Extension Educator
Iris are one of the most popular and beautiful garden flowers, and is providing great color in our gardens at this time of year. With the wide range in plant type, size, and adaptation, there is an iris for almost any location. Bearded, Japanese, Siberian, Spuria and yellow flag iris are all suitable for Nebraska. By using an assortment of these types in a variety of sizes, iris bloom time can extend from early April through June. Plus, iris are vigorous plants and easy to grow even for the beginning gardener.
Growing Bearded & Siberian Iris
Bearded iris prefer a sunny planting location with good air circulation and well-drained soil. Sandy loam soil is best, but other soil types can be amended with compost or organic matter to improve soil quality. One possibility for areas with very poor soil is to create raised beds, making soil improvement easier and improving drainage.
Siberian iris thrive under a wide range of soil conditions, including damp or wet soil, but still prefer full sun for best flower development.
Whether plants are grown in a raised bed or not, loosen the soil to a depth of at least 10 inches before planting to make root establishment easier. Keep established plantings growing vigorously by fertilizing in spring, or after blooming, with 1 pound of 5-10-5 fertilizer per 100 square feet.
Dividing & Transplanting Bearded Iris
Mid-July to early-September is the best time for dividing and transplanting bearded iris. This ensures adequate root growth and establishment before winter. Bearded iris grow from an enlarged underground stem called a rhizome. All that is required is a few inches of firm, healthy rhizome with well-developed roots and at least one fan of leaves to start a new plant. Dividing and transplanting too-thick iris beds every three or four years is an important maintenance practice that ensures plants have adequate room to grow, and minimizes the effects of iris borer, a common garden pest.
Before dividing, cut the leaves to about one third of their full height. Dig up the entire clump of rhizomes and brush away the soil. This will make it easier to decide where to divide the rhizome and which, if any, parts need to be discarded. Trim away and discard old sections of rhizome that don't have leaves, and those that are rotting or brown inside. Divide the remaining healthy rhizome sections so that each portion has at least one fan of leaves. Small sections with only one fan of leaves will not need dividing again for three to five years, but will also be slower to produce a good show of flowers. Larger sections with two fans of leaves will produce flowers more rapidly, but will also require division sooner.
Space divisions 8 to 10 inches apart in the new location. Create groupings with the fans all arranged, or pointed, in the same direction to prevent plants from growing into each other in years to come. In light sandy loam soil, plant iris rhizomes just below the soil surface. In heavier soil, rhizomes should be planted so that the top edge is exposed slightly above the soil line to prevent rotting. Roots should be buried to provide good anchorage. Form a cone or ridge of soil in the bottom of each hole; place the rhizome on top of the cone and spread the roots around the outside of the cone then backfill with loose soil.
Growing Siberian Iris
Siberian iris grow from a crown with fibrous roots, in contrast to the thick rhizomes of bearded iris. Plants don't required frequent division, every 8-12 years is sufficient, but they respond well to early spring division when necessary. Dig up the plant's crown and divide the actively growing portions into good sized clumps. Discard the old sections of crown. Replant divisions at the same depth in the new location, and keep them well watered for fastest root establishment.
Siberian iris can also be transplanted in fall, but will need additional winter protection to prevent frost heaving if not given ample time to establish roots. In this case, apply a heavy winter mulch, 3-4 inches of wood chips, the first year to prevent plants from being pushed out of the ground.
University of Nebraska-Lincoln Extension in Lancaster County is your on-line yard and garden educational resource. The information on this Web site is valid for residents of southeastern Nebraska. It may or may not apply in your area. If you live outside southeastern Nebraska, visit your local Extension office
Contact Information University of Nebraska-Lincoln in Lancaster County
Web site: lancaster.unl.edu
444 Cherrycreek Road, Suite A, Lincoln, NE 68528 | 402-441-7180