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Laura Seitz, Deseret Morning News
Makes Scents is an uncommonly fragrant iris.

LAYTON — Finding the perfect plant is never easy, but when looking at flowering perennials that are easy to grow in Utah, irises are near the top of the list.

They tolerate heat and drought, and they're almost pest free. Best of all, they have some of the most spectacular flowers of any of the perennials.

One of Utah's most enthusiastic iris growers is Helen Criddle. For many years she tended the iris collection at the Utah Botanical Center when it was located in Farmington. While doing that, she and others expanded the collection into the finest in the state.

Criddle gardens with her husband, Val, in Layton, not too far from where she grew up.

"I grew up in West Layton on a farm and always worked the soil. I always loved these flowers when I was a young child," Criddle said. "My grandmother, who lived in Woodruff, always grew the beautiful blue flowers that we called flags at that time. Of course, we do not call them flags anymore; we call them iris.

"It was from her garden I really learned to love these flowers."

Woodruff, located in Rich County, is one of the coldest spots in the state, with an average frost-free growing season of 57 days. This illustrates just how tough irises really are.

Criddle got involved with the Utah Botanical Center's iris collection after taking a master-gardener class at Utah State University. "I needed to fulfill my volunteer hours, and I volunteered to help with the iris," she said. "When we got word the old gardens were going to be relocated, we carefully dug and moved the plantings. We planted them in beds and carefully cared for them because we wanted to preserve the collection for inclusion into the relocated gardens."

She still manages the collection at the Kaysville location. Thanks to generous donations and other acquisitions, there are some 600 varieties of iris at the gardens. They are still in holding beds but will be planted in the gardens as they develop.

According to Dave Anderson, project director of the center, the new Legacy Teaching Garden will feature the collection of the iris and the daylilies that were moved from the old botanical gardens in Farmington.

The gardens will feature all irises that have been selected as Dykes medal winners. The Dykes medal is awarded to the most outstanding iris varieties in the country by the American Iris Society.

Irises grow from and are propagated by fleshy underground stems know as rhizomes. These stems grow larger and spread each year, and they sustain the plant in times of drought or other unfavorable conditions.

Criddle enthusiastically shares her love of irises. "They are one of the easiest perennials to grow. Keep them clean, and keep the plant free from debris. Do not mulch them too heavily or let the mulch pile up on the rhizomes."

After they finish blooming, Criddle advises that they be divided if they're too crowded. She said the plants can be divided anytime from July through October. "You just need to replant them early enough to get established before cold, harsh weather comes," she said.

Irises are not susceptible to many pests, but there are two. The iris borer is not common in Utah, but occasionally we see it. It attacks the rhizomes and destroys them. Soft rot is another disease that rots the tubers. If you see rotted tubers, dig them up and throw them away. Don't try to compost them.

Irises can be planted almost any time. Try to prepare the beds a couple of weeks beforehand and add organic matter to help improve the soil.

Make the holes deep enough to accommodate the roots, but do not bury the rhizomes too deep. If you cover the rhizomes more than an inch deep, they will likely not bloom.

Another important aspect of growing irises is to plant them in the right area. They must get at least six hours of direct sunlight each day. More sunlight will help the plants grow even better.

Fertilize your plants sparingly. Use a low nitrogen fertilizer in the spring when the crocuses are in bloom. After the irises get done blooming, you might want to apply a light application of a general-purpose fertilizer.

When asked to name some of her favorite irises, Criddle hesitated. "For me, my favorite iris is the one that I am currently looking at."

"I always recommend that people plant several different types of iris to get a longer bloom season," she said. "Some iris bloom very early while others bloom much later. There are also some reblooming iris, but I have not have had too much luck with them except for the miniatures," she said.

When you refer to iris most people think of the tall bearded iris that grows 36-48 inches high. Other bearded iris types include the intermediates and the miniatures. These groups are defined by how tall the plant grows. But there are other types as well.

The spurias and the Siberian iris grow well in Utah; however, the Louisiana, the Japanese and some other types are more difficult to grow here.

Finding good iris varieties to grow in Utah is easy. The hardest task will be limiting your choices from the many hundreds of different varieties that are available.

Larry Sagers is the regional horticulturist, Utah State University Extension, at Thanksgiving Point.