If you’re looking for an indestructible perennial to grow along Colorado’s Front Range, you can’t beat bearded irises. They’re tough, hardy to zone 3. They’re drought tolerant. They aren’t fussy about soil. Deer and rabbits leave them alone (for the most part). And they come in nearly every color in the rainbow—and then some. How can you lose?
Bearded irises are just one variety of iris, a genus that includes several hundred species. While the varieties we’re familiar with are derived from their ancestor Iris germanica, native to southeast Europe, bearded irises as we know them are the result of hybridization, and are not found in the wild. Because of this, it’s better to describe them as Iris x germanica, or simply Iris ‘[cultivar name].’ Another common name for bearded irises is “flags.”
Most of us recognize irises in the garden. Their sword-shaped leaves rise from rhizomes, appearing as soon as the soil begins to warm in spring. Flowers top long stems that also start at ground level. Stems typically grow in a zig-zag pattern, holding several blossom that open in sequence. A couple of cultivars are grown, not for their flowers, but for their variegated leaves, which come in green-and-silver, or green-and-gold.
Irises are segregated according to size, ranging from 2 to 6-inch miniature dwarf plants through standard dwarf and intermediate irises, to tall irises measuring from 28 inches to more than 3 feet in height. Bloom time is related to height, with the shorter cultivars blooming first, in early May, and the tallest finishing up as late as the end of June, especially at higher elevations.
When describing iris flowers, growers use some special terminology. The flowers have six petals, three growing upward and three pointing downward. The latter are often called “falls” (easy to remember, as they “fall” toward the ground). The upright petals are called “standards.” The “beard” lies at the base of the falls. All the petals may be the same color, or the standards, falls, and beards may all be different, creating lovely contrasts.
Originally a soft lilac purple, the flowers are now available in almost every imaginable hue, from icy white through a purple so deep it appears black. There are even brown flowers. The only color missing is bright red—and I’m sure it’s only a matter of time and breeding before we can enjoy crimson irises as well.
Irises are incredibly easy to grow here in Colorado. For best bloom, pick a spot in full sun. Place the rhizomes root-down. Don’t bury them too deep—they like to be near or at the surface of the soil. Finally, cover with a few inches of mulch. While better soil is appreciated, too much organic matter can cause the soil to hold too much water, and good drainage is essential. Soggy soil is the one sure way to kill these tenacious plants.
The plants will continue to expand outward as the rhizomes grow. Good results come from clumping three plants about a foot apart, facing the growing tips (where the leaves are) away from one another. When clumps get too dense (usually in three to five years), dig them up and separate the pieces. Friends and neighbors are usually happy to receive the extras. The traditional time to dig and separate irises is in August after they have bloomed, giving them the maximum time to become established before it’s time for the next year’s bloom. However, it can be done at any time during the growing season.
You can see some helpful photos of this process at the Long’s Iris Gardens “Growing Tips” page—although I see no need to trim the leaves, and in fact advise against it. The plants can use the food those leaves produce to become established.
(By the way, I enthusiastically recommend this source of new plants. I’ve been exceedingly happy with their products and exceptional service. If you have time and live near Boulder, Colorado, try to visit in late spring while they’re open to the public, and especially during their Memorial Day weekend open house. You’ll delight in the fields of irises in full bloom. I might even see you there!)
Aside from dividing overgrown clumps, care is minimal. Growers recommend removing any developing seed heads after bloom, so the plant puts its energy into growth and not seeds. In late March, when new growth starts, last year’s dead leaves come off with a gentle tug. There’s no need to cut them back before that, unless the browning foliage in fall bothers you.
If aphids become a problem (rare), knock them off with a strong spray of water, or relax and wait for the “good bugs” to do the job for you.
I like to plant my irises as vertical accents in my landscape. That way the distinctive leaves continue to serve a design purpose even when their flowers are finished for the year. Irises combine well with other low-water perennials such as catmint, lamb’s ears, or red valerian (Jupiter’s beard, Centranthus ruber). The shorter cultivars make good rock garden plants, while the taller varieties can be nestled in the middle of a border, with shorter plants screening their base.
I’d like to give you an example of how resilient irises are. Our daughter’s in-laws grow hundreds of iris cultivars on their property in Tacoma, Washington. They keep bags and boxes of extra rhizomes to share with anyone who wants them. Our other daughter visited in October, several months after the plants had been dug. She took five varieties home with her to Colorado. However, she forgot to plant them. In March, she discovered the paper bags sitting in the garage, and gave them to me. “Mom, can you get these to grow?”
The condition of the roots, shriveled and dry, was pretty pathetic. They looked dead, but I figured I had nothing to lose. In April, when the ground thawed, I soaked them for a few hours, then planted them in my raised beds (where I could easily keep an eye on them). By May, green shoots were coming up from every rhizome! I moved them into their permanent location in my garden. Now, two years later, I have five healthy plants. (And no, I’m not giving them back!)