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How to Grow Irises in Your Canadian Garden

Irises are striking perennials that bring elegance and color to any garden. With the right site, soil, and annual care, they thrive in Canadian climates, producing blooms that attract pollinators and delight the eye. This guide provides seniors with clear, step-by-step tips for planting, pruning, and maintaining irises for lasting beauty.

How to Grow Irises

Planting and caring for Irises
Posted By: Michigan Froggy
Date: 2004/6/24
Irises need a sunny location in well drained, weed free soil. Till soil to a depth of 10 inches and work fertilizer into the area several days before planting.

If you have clay soil, you should mix in sand, humus and bone meal in addition to a good garden fertilizer 5-10-10 or 6-10-6. Avoid high nitrogen fertilizers, which could cause rot.

Place them in the ground with the roots spread and buried firmly with the rhizome near the surface about a foot apart. Do not plant the rhizome too deep. It is best to dig your hole and mound the soil, placing the rhizome on the mound with the roots spreading down around the mound then cover firmly with soil so the top of the rhizome is exposed to the sun.

Divide by cutting the new rhizomes away from the original plant to avoid crowding and plant them. It is better to do this one or two months after they bloom.

In cold areas where the ground freezes and thaws, a mulch of hay should be applied in the fall.

If your irises develop spots on the leaves, this is probably a fungus, which can be identified by a brownish colored spot surrounded by yellow. It is best to remove these leaves to keep the fungus from spreading, as the fungus will weaken the rhizome due to lack of nutrients caused by the dying foilage.

When transplanting irises and dividing, check for holes in the rhizomes. If you find any, discard the rhizome as this is generally caused by the iris borer.
To keep the borers away it is good to clean all debris away from the iris plants.

Another problem which could damage rhizomes is bacterial soft rot. This may enter the rhizome through any wound. To get rid of soft rot, dig the rhizome, scrape off the affected tissue, allow it to dry in the sun, then dip in a solution of household bleach and water for a few minutes. Rinse with water and allow to dry before replanting.

Do not cut back the healthy green leaves of the iris after blooming, these allow the nutrients to return to the plant. The bloom stem and any diseased or brown leaves may be cut back.

If you have Japanese Iris, they like wet, sunny locations, with and acidic soil and regular fertilizing. They should be transplanted or divided in early spring.

Something I didn't know is that stalks that produce flowers one year, will not produce flowers again, but should be left to provide nutrients to the side shoots which may bloom the following year.

Hope this helps everyone. I will have to divide mine next month and replant in an area where they will have more room. I didn't know you were supposed to divide them.

Notes from Lion Gardener:

I noticed a tiny hole in one iris rhizome while dividing my plants today. When I cut into it, I found a fully grown iris borer about 2 inches long hiding inside. I was able to remove the damaged tissue and save part of the rhizome. If you find a soft or hollow rhizome with a small entry hole, it's worth investigating before the damage spreads.

How big are they?

Newly hatched larvae (May): about 2–4 mm (1/16–1/8 inch)
Growing larvae (June): about 12–25 mm (½–1 inch)
Full-grown larvae (July): 38–50 mm (1½–2 inches) long
By the time they're full size, they're surprisingly large and quite robust.

Typical characteristics:

Pinkish-white to cream-coloured body.
Brown or reddish-brown head.
Sometimes a faint pink tint develops as they mature.
Smooth body with no obvious hairs.

Their life cycle is roughly:

Fall: Adult moths lay eggs on old iris leaves.
Spring: Eggs hatch when new iris leaves emerge.
May–June: Tiny larvae tunnel down the leaves.
June–July: They enter the rhizomes and grow rapidly.
Late July–August: They leave the rhizome, burrow into the soil, and pupate.
Late summer/early fall: Adult moths emerge and lay eggs for next year.

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Page Updated by: Lion Gardener July 2026

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