Growing Iris in Manitoba

By Barbara Jean Jackson, Master Gardener and President of the Can-West Iris Society

 

Iris predominate in my gardens. From the tiny miniature dwarf bearded types that confirm spring is here to the later blooming and magnificent tall bearded, Siberian, spuria, and species iris, my gardening season is defined by what iris is blooming at the time. Because of the different types I grow, quite often I have them in bloom from mid-May to mid-July, depending on the year, more than half of our too-short growing season!

What do you need to do to grow these beauties? How do you know if the type and cultivar you want to plant will thrive in your garden and not just fade away?

First, an understanding of the classification system of bearded iris as well as how to plant and care for them is needed. For the most part, iris are relatively easy to grow once you know how.

Bearded iris are classified according to height: Miniature Dwarf Bearded (MDB) — under 8 inches; the Medians, including Standard Dwarf Bearded (SDB) — 8 to 15 inches; Intermediate Bearded (IB), Miniature Tall Bearded (MTB) and Border Bearded (BB) — 16 to 27 inches; and Tall Bearded (TB) — over 27 inches.

They vary in height, but also in flower form, available colours, and patterns. They also vary in survivability, which is why I concentrate primarily on the Median types and MDBs. Some people are able to grow the modern tall bearded iris well in our harsh growing climate, but I am not among them.

Bearded iris grow from an enlarged stem also known as a rhizome that provides the leaves, flowers, and roots that anchor the plant. The rhizome is vegetatively propagated to make new plants. All you need is a few inches of firm, healthy rhizome with good roots and at least one fan of leaves. Generally, the median types (SDB, IB, BB, MTB) and the dwarf type (MDB) multiply more quickly than the tall bearded types.

Before planting, work the area to a depth of six inches or so and let it sit for a few days to settle. When preparing to plant, dig a shallow hole large enough to accommodate the rhizome. Leave a ridge of soil in the center, place the rhizome on top and spread the roots out around the ridge. The rhizome should be just at or slightly below the soil surface. Fill the hole with soil and firm around the roots and rhizome. Water thoroughly immediately after planting but afterward, water sparingly until new growth begins.  Ideally, they should be planted 18 inches apart but really, who has that much room. Just give them enough room so they can spread out a bit and not grow into each other. In my experience, the Standard Dwarf and Miniature tall bearded types require the most real estate. And label carefully so you know who is who. “I’ll remember that one” doesn’t work very well in my experience, hence the number of Noids (no identification) I have. Many are distinctive, and the names come to me without thinking, but many do not. I try to use two labels, one under the ground and one beside it.

The growth rate slows down in mid-summer after blooming (mid-July to mid-August). This is the period of time when the buds for next year’s bloom are formed. Planting early enough to avoid cold damage to these buds is very important. For best survival rates on the prairies, tall bearded types should be planted before the end of July. Medians and dwarf types generally can safely be planted until mid-August. This is the best time, too, to divide and replant clumps so they have time to establish new roots and get ready for winter. Generally, four to six weeks is needed.

To keep iris clumps looking their best and producing good blooms, divide and replant every two to five years depending on type and cultivar. Iris need the same good cultural care as other perennials. Eliminate competition from weeds and grasses to increase air circulation in and around them to prevent rot, particularly in a wet season.

Newly planted iris may need to be winter mulched. Put mulch in place in late fall, preferably after the ground is frozen. If there is snow on the ground, mulch over the snow. The biggest advantage to using mulch is to reduce freezing and thawing of the soil that can push plants out of the soil. This is a common problem here. Be on watch for plants that have been heaved out of the ground and firm them back in place. I use an appropriately sized rock as an anchor.

After the snow and ice have melted away in the spring, remove the mulch. Do this in several stages and carefully. Damage to the centre of the plant may prevent flowering. Carefully remove dead outside leaves. Do not compost iris debris as leaf spot spores can hide in dead foliage.

The ‘Other’ Irises

Beardless iris are as they sound; they have no beards. There are many types of beardless iris of which the Siberian and spuria are most popular. Of these, the Siberian are the hardiest, particularly the historic (more than 30 years old according to the Historic Iris Preservation Society) and more old-fashioned types. The modern hybrids can be more demanding.

Siberian iris grow from two to four feet in height and most have thin grasslike foliage. They bloom at the end of the tall bearded season. They are very effective in naturalized settings and perennial borders and can be left in place for many years before needing to be dug and divided. Siberians perform best in full sun but can tolerate less. They like year-round moisture, but not soggy conditions. Good drainage is critical. A light fertilizing in the spring and again after bloom encourages strong growth and good bloom.

Newly purchased or received rhizomes should be soaked in water overnight before planting. Cover the rhizomes with two to three inches of soil, spacing plants about two feet apart. New plants should be kept well-watered.

When the foliage dies back in the fall, it has a tendency to flop, so if you like things neat and tidy, cut the foliage back as far as you like. They need two to three years to become fully established; the first year’s bloom is not representative, if present. If you are like me and refuse to give them supplemental watering, they may not bloom every year, particularly the more modern hybrids.

Spuria culture is similar to the culture of the Siberians. These iris display large, open blooms atop tall, rugged plants about one to two weeks after the tall beardeds. They grow well in all types of garden soil. Full sun and good drainage are the main requirements. They do not like wet feet.

When planting, cover the rhizomes with two inches of soil. Space plants at least two feet apart. After planting, water in well and water regularly until plants are established. In future years, the plants need water before bloom, but there is no need to water after blooming, although doing so won’t hurt them. An application of composted manure or commercial fertilizer will enhance growth. Do not expect peak performance until the third or fourth year. Spurias should be left alone for years, allowing the plants to grow into the large clumps for which they are known. I am relatively new to growing them. My initial attempts were failures, and I was not going to try again until an iris friend gifted me with a hefty division of an older hybrid (‘Dutch Defiance’). It bloomed for the first time in 2021 in its fourth year in my garden with a single bloom. In 2024, it had three blooms.

Japanese iris, also called Japanese water iris, (Iris ensata) are not reliably hardy here. Some have reported sparse bloom but the plants do not do well in the long term. I tried one once and after five years of just foliage, it finally died. I also grow several more exotic species of irises, each with its own very specific cultural requirements. They are not recommended for new iris growers.

The genus iris also includes various bulbous types including Dutch iris (Iris hollandica) and netted irises (Iris reticulata). Unfortunately, they are not hardy in Manitoba unless you have a very sheltered microclimate in which to grow them. I have never been successful.  It is unfortunate since one of the world’s most prominent reticulata hybridizers, Alan McMurtrie, is from Canada.

Unfortunately, I also have to report that the dreaded iris borer has been found and confirmed in a few gardens in southern Manitoba. The damage the pest can inflict is significant and vigilance is key. Because its occurrence is so new and most growers do not know what to look for, I would recommend joining the private group on Facebook for the Can-West Iris Society where some lively discussions have taken place about them the last few years, including pictures and the damage they cause. It is rather horrific.

You might ask where you can get more information on growing iris in cold areas? The Can-West Iris Society (CWIS) has the answers to your questions. Check out the website at http://www.can-westis.com.