A Guide for Growing Bearded Iris

My bearded irises grow quite happily without too much fuss. After they’ve bloomed, it’s tempting to ignore them for the rest of the growing season.

But in high summer (July and August), it’s time to look at them and decide if they’re crowded and need to be dug up and divided. Fortunately, this is a pretty easy task. You’ll end up with more irises to plant elsewhere in your garden or share with friends and family.

What Is a Bearded Iris?

One of the most popular iris varieties, bearded irises (aka German irises) bloom in mid to late spring, depending on the type. The flowers feature three upright petals, called standards, and three drooping petals, called falls. Each fall has a tufted beard, hence its name.

Most bearded irises grown today are hybrids, with the botanical name Iris x germanica. Hardy in U.S. Department of Agriculture Plant Hardiness Zones 3 through 9, they come in almost every color. Many feature bicolored flowers, with falls of one color and standards of another.

Types of Bearded Iris

The American Iris Society classifies bearded irises based on their height, ranging from miniatures only eight inches tall to ones that grow to almost three feet. Bloom times vary from early to late spring. Some, like Immortality and War Chief, re-bloom later in the summer.

How To Grow Bearded Iris

Planting

Bearded irises are commonly planted from July through September. They can also be planted in spring if purchased as a growing potted plant.

Choose a location with excellent drainage and full sun. Bearded irises grow from rhizomes, fleshy underground structures that can rot in wetter soils. Before planting, turn over the soil to loosen it up. Remove any weeds. If you have heavy clay soil that doesn’t drain well, add sand and mix it well.

Plant the rhizome just below the soil surface, barely covering it, with the roots in the ground. Don’t cover it with mulch, which can lead to rotting.

Fertilizing

Depending on your soil, you may not need to fertilize your irises once they’re established. If you’re unsure or know your soil lacks some nutrients, work in a general fertilizer when preparing the bed for planting.

Watering

Established irises generally do not need additional watering and will even tolerate periods of drought. Water well after planting, but make sure the irises aren’t standing in water.

Deadheading

After your bearded irises have flowered, cut off the flower stems to encourage the plant to grow stronger rhizomes instead of seeds.

Pests and diseases

Irises are not bothered by many pests or diseases, except for one — iris borers.

Inspect your irises in spring and summer for signs of iris borer caterpillars. According to the University of Minnesota Extension, these first chew holes in the leaves, then burrow down into the rhizomes. Check for brown streaks on the foliage.

If you find the borers on the leaves before they reach the rhizomes, crush them in the leaf or cut off that leaf to destroy them. If you find iris borers in the rhizomes, dig those up and discard them.

Always remove and discard iris foliage in the fall after the first frost to prevent iris borers in the leaves from overwintering.

When Can I Dig and Divide Bearded Iris?

As mentioned above, the best time to dig and divide bearded irises is a month or two after flowering, usually July to August. Healthy bearded irises will generally get crowded after two to three years in the same spot. Then it’s time to divide them.

Dig up the entire clump of irises at one time. You will find several new rhizomes attached to the older or original rhizomes. Carefully separate those so you end up with at least one “fan” of the spear-like leaves and roots attached to each rhizome.

Cut the leaves back, leaving them about six to eight inches long, then replant the new rhizomes. Old rhizomes can be discarded. Share your extras if you have more rhizomes than you want to replant.