How to Grow Siberian Iris

Siberian Irises are such easy, reliable perennials that I tend to take them a bit for granted. I have three different cultivars in my backyard; an indigo blue, a medium purple and a dark inky-blue. I planted them well before I began this blog and started keeping track of plant tags, so I am sorry but I won't be able to identify them for you. The most striking of the three is the deep navy blue iris my Mom gave me.

The Siberian Irises you find in most gardens are a hybrid of two species iris; Iris sibirica and Iris sanguinea.  The two species plants are found primarily in Central Europe and Asia. They grow in grassy meadows which become flooded by streams that surge with runoff from melting snow every spring.

Siberian Irises bloom in mid-spring to early summer (in my zone 6b garden, that's early to mid-June). To be honest, I find their floral display is a bit brief for my liking (approximately 2 weeks) and their foliage can look a bit messy once they've flowered. On the plus side, Siberian Irises flower early in the gardening season when not much else is blooming. They are also relatively low maintenance. After weighing all these characteristics, I still think Siberian Irises are well worth having in your garden.

 Piper among the irises and self-seeded Sweet Rocket (mauve flower).

A purple iris in my garden.

The Siberian Iris I brought home from my Mom's garden.

Here's a quick list of the growing requirements for Siberian Iris:

Light

Full sun is generally recommended for irises. In my garden, the Siberian Irises get morning sun with light afternoon shade and that seems to suit them just fine. I think this works well because conditions here are on the dry side and they get a break from the scorching sun on hot summer afternoons. In terms of the sunlight levels, it seems to be a delicate balancing act–if there was any more shade, I think my Siberian Irises would struggle to grow and bloom.

Soil

Siberian Irises flourish in soil that is rich in organic matter. They also prefer soil that is slightly acidic, they are remarkably adaptable to average garden soil.

Planting

Unlike bearded iris, Siberian Irises don't like to have their rhizomes exposed to sunlight. Instead, cover the rhizomes of bare-root plants with one to two inches of soil. If you purchase a Siberian Iris in a pot, the soil in the garden should be level with that in the pot. Place plants 1.5-2 feet apart. Water them and continue to provide water regularly in their first season.

Fertilizer

The Canadian Iris Society recommends an application of fertilizer early in the spring that is higher in nitrogen, followed by a balanced fertilizer at the end of the bloom cycle when the plant enters a growth phase.

Moisture

Fortunately for me, Siberian Irises like moisture in the spring but are adaptable to somewhat drier conditions in the summer. Providing adequate moisture throughout the growing season will, of course, encourage healthier, bigger clumps.
If you top dress with a layer of organic matter, it will help conserve moisture and keep the soil cooler for your irises.

Pests

I have yet to experience a pest problem with any of my Siberian Irises. They seem to be much more resistant to disease than my bearded irises. While I have been lucky, Siberian Irises can sometimes fall victim to iris borer.
Adult borers are nocturnal moths that lay their eggs on garden debris in late summer or fall. They hatch into one-inch sized larvae that chew their way into the leaves and eat their way down to the rhizomes. Borer damage is often seen as notched wounds or slimy, wet-looking areas on the foliage. Once they eat their way down to the base of the plant, they begin to hollow their way through the rhizomes. In August, they pupate in the soil and hatch into more adult moths.
To deter this pest, keep the rhizomes of your Siberian iris clear of any debris throughout the growing season.

Transplanting and Dividing

Siberian iris can be left undisturbed for several years. You'll know it's time to divide your clump when fresh growth is less vigorous and there are fewer and fewer flowers.
The time to divide older clumps is right after they flower. Over the years, my Siberian Irises have grown into huge clumps–so big I foolishly put off the hard work of digging them up and dividing them. Last spring I finally transplanted smaller pieces to the perimeter of what I hope will be our new pond.
Clumps can be as small as 2 to 4 fan divisions. Don't let the exposed roots of your divisions dry out while you dig a new hole. Place them in a shallow bucket of water while you're working. When you plant the divisions, the rhizomes should be about an inch below the surface (slightly deeper in sandy soil).
 The time you want to spoil your plants with regular watering is right after you transplant the divisions. It will really help them get re-established in their new spot. Keep in mind that it may take as many as 6-8 weeks for them to settle in, so keep a regular watering regime going well into the summer.

Growing Siberian Iris from Seed

If you would like to grow Siberian Iris from seed, leave a few flowers to mature into seed pods. When the seed heads are ripe (in the early fall), they will open slightly at the top. Shell the seed pods. From here there are different ways to proceed. The easiest method is to sow the seeds directly in the fall. Seeds can also be stored in a cool dry place for the winter. I am going to defer to the experts on the Canadian Iris Society website when it comes to the subject of successful germination because it appears to be quite complicated. Here's a link to their advice.

Cultivars

Siberian Irises come in a wide range of colours; blue, purple, white, yellow, white, orange-brown and warm shades of pink or reddish-purple. Here's a quick look at some irises just to give you an idea of the wide range of colors available:

Iris Sibirica 'High Standard'

Iris Sibirica 'Strawberry Social'

Iris Sibirica 'Ranman'

Iris Sibirica 'Royal Herald'

The Canadian Iris Society has a list of plant sources for both Canada and the US (scroll down a little when you get to the Society's webpage). Most nurseries will offer a limited selection in the spring. Mail-order sources offer the biggest array of plants but sadly, for those of you wanting to plant irises this spring, most of these companies do not ship until the fall.

Companion Plants

Siberian Irises look quite nice in groups of two or three complementary colors. Other companion plants should bloom mid-spring, like full sun to part shade and average to moist soil.

A Siberian Iris (right) combined with a dark blue Salvia (centre foreground), a hardy geranium (lower left corner) and Centaurea hypoleuca 'John Coutts' (see in detail below) at the Royal Botanical Garden in Hamilton. 

Knapweed, Centaurea hypoleuca 'John Coutts' is a clump-forming perennial that has lavender-pink flowers and deeply cut grey-green leaves. It is quite happy in poor to average garden soil (it may require staking in rich soil). Deadhead the flowers to encourage reblooming. Attractive to butterflies. Full sun. Height: 50-60 cm (20-23 inches) Spread: 45-60 cm (18-23 inches). USDA zones: 3-9.

An unknown type of Siberian Iris paired with a Ligularia and Allium 'Purple Sensation' 

Top row from left to right:

Hardy Geraniums (Cranesbill) The short, rounded shape of hardy geraniums makes them a nice perennial to grow at the feet of a Siberian Iris. Full sun to part-shade.

Lupins have tall floral spires in shades of pink, lavender, purple, red, maroon and white. They like full sun to light shade and moist, well-drained soil. Read more here.

Columbine is a short-lived perennial that have an array of flower forms and colors. Full sun to light shade. Read more about them here.

Bottom row from left to right:

Hardy Salvias have vertical flower spikes on a bushy clump of grey-green leaves. Full sun and average to moist soil.

Lady's Mantle, Alchemilla mollis has soft green foliage that sparkles with raindrops and sprays of chartreuse flowers. Full sun and average to moist soil.

Peonies have big round blooms that contrast nicely with the smaller flowers of a Siberian Iris. Full sun and soil with average moisture.

Siberian Iris (lower right) with Salvia (spikey navy flower in the middle), Crambe Martinia (lower left) and Knapweed, Centaurea hypoleuca 'John Coutts' (behind the metal bench).

Some gardeners will tell you Fumitory is a nuisance self-seeder, but it is easy to pull out where unwanted. It makes a nice companion at the foot my Siberian Iris.

Plant type: Perennial

Height: 2.5-3.5 ft

Spread: 2-2.5 ft

Flower: blue, purple, white, yellow, brown, orange shades and warm shades of pink or reddish-purple

Bloom period: Spring

Leaf: Silvery blue-green to fresh green

Light: Full sun/ light afternoon shade

Growing conditions: Moist, rich, somewhat acidic soil

Move or Divide: In spring after they flower

Problems: Iris Borer

USDA Zones: 3-8



I think you'll find the Siberian irises are a wonderful addition to the garden mid-spring.

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