My irises didn’t bloom at all in 2022. What’s going on?
—Julie T. from Facebook

Given the right conditions, irises are reliable bloomers and provide color when not much else is flowering. If your irises aren’t blooming as prolifically as you’d like, check these five factors.

Sun

Most irises require at least six hours of sun daily for full bloom. If that’s your issue, move them to a sunnier site or trim vegetation that is shading them. You can even enjoy irises if your garden is less sunny by planting the low-growing crested iris, which will spread to form a groundcover.

Moisture

Irises tolerate drought but do need watering when the soil is extra dry. If the soil near your plants feels dry down to 3 inches, then water. Don’t overdo it; too much water can lead to rhizome rot.

Crowding

Irises need to be divided periodically, usually every three to five years, to continue blooming well. To divide, lift the clump, and gently tease or break apart the bulbous rhizomes. Division is easier if you trim the iris foliage to about 6 inches, shake off the soil, and use your fingers to gently remove the young bulbs. As a bonus, you now have more irises to plant.

Rhizome depth

When you replant those rhizomes you’ve just teased apart, place them root side down with the upper portion of the rhizome left uncovered. Planting too deeply can reduce blooms. Water them well until they take hold. The best time to divide irises is one to two months after bloom, usually in late July or August.

Nutrients

Using a fertilizer with too much nitrogen will generate healthy leaves but not beautiful blooms. Irises prefer a fertilizer mix with more phosphorous, the middle number on the fertilizer bag.

A 5-10-5 or a fertilizer labeled for bulbs should do the trick. Sprinkle a little of the mixture around
(but not on) the plant both before and after bloom. Irises are a great plant to fill that void in your garden after the spring beauties fade and before the summer perennials kick in. With almost 300 species in all sorts of colors and forms, this is one plant you don’t want to miss.

NORTHERN IRISES

Northern gardens host three types of iris: bearded, Siberian and Japanese. Bearded
iris is the most popular, offering hundreds of varieties and colors. Even after their blooms fade, irises offer striking vertical stalks, a design feature that contrasts nicely with other foliage.

WHERE TO SEE IRISES

For a display of a variety of irises, visit the Northeast Minneapolis Municipal Iris Gardens (nemmig.org) throughout the season. The Minnesota Landscape Arboretum also has an iris garden and most public gardens feature irises in June, including the Duluth Rose Garden and the Munsinger Clemens Gardens in St. Cloud.

FOR MORE INFORMATION

Minnesota Iris Society, irismn.net

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This article originally appeared in the Summer 2023 edition of Northern Gardener® Magazine.

Diane McGann is an award-winning garden writer and the design columnist for Northern Gardener magazine. She also serves as a University of Minnesota Master Gardener and Tree Care Advisor. Diane has both studied and taught landscape design, her particular gardening passion. She serves on the University of Minnesota Extension Ask an Expert panel and is a member of Garden Communicators International and the Washington County Horticulture Society. Diane resides in Stillwater where she maintains extensive perennial and shade gardens on her 4 ½ acre property..