Siberian iris (Iris sibirica) is one of the toughest and most graceful irises you can grow, with elegant blooms in late spring to early summer held above slender, grassy foliage that stays attractive long after the flowers fade. It is hardy in zones 3 to 8, which makes it dependable in almost every Canadian garden. Check your own zone with our hardiness zone finder if you are not sure.
While it enjoys moisture, Siberian iris is far more adaptable than its cousin Japanese iris. It grows happily in an ordinary perennial border as long as the soil does not bake dry, which makes it the easier choice for gardens without a damp spot.
When to Plant
Plant Iris sibirica rhizomes in spring, when the soil is workable and temperatures begin to warm. These hardy perennials establish readily outdoors and are well adapted to cold winters, so spring planting gives them a full season to settle in.
Where to Plant
Choose a location in full sun for the strongest growth and best flowering. Siberian iris prefers fertile, well-drained soil that stays consistently moist through the growing season.
It performs beautifully in perennial borders, along streams, near water features, or anywhere the soil does not dry out completely. In a sunny border it combines especially well with daylilies, which enjoy the same conditions and pick up the display just as the iris finishes blooming.
How to Plant
- Dig the hole. Make it wide enough to hold the rhizome comfortably.
- Set the depth. Plant rhizomes about 5 cm (2 inches) below the surface, with the roots fully covered and any emerging shoots left above ground.
- Backfill and firm. Fill in with soil and press gently into place.
- Water thoroughly. A deep watering establishes good root-to-soil contact.
Space plants 15 to 20 cm (6 to 8 inches) apart. That leaves room for growth while still creating a full display as the clumps knit together.
Ongoing Care
Watering. Keep the soil evenly moist, especially during active growth and flowering. Siberian iris appreciates moisture, but avoid spots where water sits for extended periods.
Mulching. Mulch around the plants to conserve soil moisture and reduce weed competition.
After flowering. Leave the foliage in place once the blooms fade. The leaves store energy for next season, and their upright, grassy form earns its spot in the border on its own.
Autumn cutback. Cut stems and foliage back to about 3 cm (1 inch) above the soil in autumn to tidy the garden and prepare plants for winter.
Dividing. Divide mature clumps every few years if flowering declines or the centre of the clump becomes crowded.
Common Questions
Does Siberian iris need a pond or bog to do well? No. Unlike Japanese iris, it thrives in a regular garden bed as long as the soil stays reasonably moist. Damp sites suit it, but they are not required.
Why has my Siberian iris stopped blooming? Crowding is the most common reason. When the centre of a clump goes bare or bloom counts drop, it is time to divide. Too much shade is the other frequent cause.
How deep should the rhizomes be planted? About 5 cm (2 inches), fully covered by soil. This is deeper than bearded iris, whose rhizomes sit partly exposed.
Does it need winter protection? No. Siberian iris is hardy to zone 3 and handles Canadian winters without special care. Just cut the foliage back in autumn.
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