How to Grow Bearded Iris: Planting, Dividing and Care

Plant bearded iris rhizomes in late summer to early fall, in full sun and well-drained soil, with the top of the rhizome at or just under the soil surface, and divide the clump every three to five years. Clemson says irises need at least six hours of sun, are extremely drought tolerant, and should not be overwatered. Penn State says the plant thrives in USDA zones 3 to 10 and flowers in spring. The sources disagree on the best month to divide, and that range is covered below.

USDA zones

3–10 (Penn State)

Sun

Full sun, at least 6 hours (Clemson)

Origin

Middle East

Soil

Well drained

Planting depth

Rhizome at or just under the surface

Spacing

12–18 in apart

Divide

Every 3–5 years, from about 6 weeks after bloom to September

What bearded iris are

Penn State calls the tall bearded iris one of the oldest garden flowers, named for the Greek goddess of the rainbow. Bearded irises flower in spring (Penn State). The American Iris Society classes irises as bearded, aril and beardless, and Penn State says there are thousands of cultivars. This guide is about the bearded type, which grows from a rhizome, a thick horizontal stem at the soil surface.

Sun, soil and water

Sun. Clemson says at least six hours of sunlight a day.

Soil. Clemson says well-drained soil. Clemson also says irises are extremely drought tolerant and that care should be taken not to overwater them.

Fertilizer. Clemson recommends a low-nitrogen fertilizer such as 5-10-10 in early spring and again at the end of the season. It says a high-nitrogen fertilizer may make the plants grow too rapidly and lead to soft rot.

How deep to plant the rhizome

Iris rhizomes are planted shallow. Clemson says the rhizome rests just above ground level on clay soils, and for lighter, sandy soils the top of the rhizome can be placed 1/2 inch or less below ground level. Illinois Extension says not to plant the rhizome too deep because this can lead to root rot. Clemson says to space divisions about 12 to 18 inches apart in groups of three to form a natural-looking clump. Illinois Extension also gives 12 to 18 inches, with the fan of leaves facing the same direction.

When to plant and divide

Clemson says irises should be planted in late summer to early fall in well-drained soil. Penn State says rhizomes can be bought bare root from many online sources and some garden centers for late summer planting. Clemson says to divide bearded iris every three to five years, and to plant the younger rhizomes that grow off the older center rhizome.

The best month to divide is where the sources differ.

Put together, the window runs from about six weeks after the spring bloom through September, with July and August named by both sources. If you divide in July or August you are inside both windows.

Planting and dividing steps

1. Dig the clump. Divide when the plant is crowded or every three to five years (Clemson).
2. Choose the younger rhizomes. Clemson says to replant the younger rhizomes produced off the older, center rhizome.
3. Plant at the surface. The rhizome rests just above ground on clay, or 1/2 inch or less below on sandy soil (Clemson).
4. Space them out. 12 to 18 inches apart, in groups of three, fans facing the same direction (Clemson, Illinois Extension).

After bloom

Clemson says to remove the flowering stalk after bloom, to prevent seed from forming and stealing energy from the plant. Our iris pruning guide covers the fall cutback.

Common iris problems

Grow these next

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