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How to Grow, Maintain, and Divide Bearded Iris

Expert Tips

It's magical when bearded irises unfurl pencil-slim buds to reveal a kaleidoscope of color in spring. Once called flags, these perennials flourish in USDA Zones 3-9 where winter temperatures dip below freezing, allowing dormancy.

"Anyone can grow iris," says Doris Winton, master judge for the American Iris Society. While fragrance has diminished through hybridization, bloom size and color palette have increased. "Every color except fire-engine red can be found in bearded iris."

Learn more about growing and caring for iris in our Plant Encyclopedia.

Iris Growing Tips

Plant in a sunny spot in late summer. Well-drained soil, at least 6 hours sunlight (full day better to keep rhizomes dry). Rhizomes are fleshy rootlike structures at the base.
Prepare beds. Low-nitrogen fertilizer, soil pH slightly below 7 (neutral). Apply granular fertilizer twice yearly—early spring and after bloom when rhizomes form next year's flowers. Water only if extremely dry or after transplanting.
Give room to breathe. Good air circulation; plant 16-18 inches apart (less for dwarfs, more for tall).
Do not mulch. Mulch retains moisture, causing soft rot of rhizomes.
Break off seedpods after blooms fade. Prevents seedlings choking soil; seed formation saps energy from rhizomes, roots, leaves.
Prune foliage in fall. Reduces overwintering pests and diseases.
Make dividing a habit. Divide clumps every 3-4 years in late summer. (See next page for detailed instructions.)

Related Garden Plan: Pink and Blue Garden with Iris

How to Divide Bearded Iris

'Avalon Sunset' (apricot); 'Throb' (yellow); 'Syncopation' (violet-orange, brown edges)

Bearded iris produce leaves, flower stems, and roots from a thick rhizome. As the plant matures, the rhizome produces more rhizomes, leading to more leaves and flowers. Over time, the original rhizome withers and dies, slowing bloom production. Division removes and replants baby rhizomes so they can develop.

Divide in late summer when weather cools. Process works for other rhizomatous plants: canna, bergenia, dahlia, toad lily, lily-of-the-valley.

Learn more about how to grow reblooming irises.

Step by Step

1. Carefully dig clumps with garden fork or spade, avoiding chopping rhizomes.

2. Divide rhizomes by pulling apart with hands. Use sharp knife if needed; dip in 10% bleach/water between cuts. Good rhizome: thumb-thick, healthy roots, 1-2 leaf fans. Discard large old rhizomes with no leaf fans.

3. Wash soil off rhizomes to inspect for iris borer (fat white worm). Destroy if found. Some wash in 10% bleach solution for disease protection, but won't help already rotting plants.

Destroy soft, smelly, or rotting plants. Discard lightweight, hollow, dead-looking rhizomes.

4. Clip leaf blades to 4-6 inches. Reduces stress as plant concentrates on regrowing roots instead of maintaining long leaves.

5. Replant divisions, setting rhizome higher than fine roots, which should be fanned out. Top surface of rhizome just visible at soil surface.

6. Space plants 12-18 inches apart (closer for dwarfs, farther for largest). For best display, plant so leaf fans face same direction. Water well at planting; don't continue unless weather becomes dry.

Some Great Irises

Iris flowers have three primary structures: drooping "falls," upright "standards," and fuzzy "beard." Descriptions refer to these parts. Example: 'Fringe of Gold' has white falls picoteed in yellow, solid yellow standards, white beard.

Doris Winton's favorites include 'Fringe of Gold'. See below for more.