Irises: Complete Guide to Planting, Growing, and Dividing Bearded and Siberian Types

The tall, elegant iris, named for the Greek rainbow goddess, graces gardens in magical colors. Every gardener wants this reliable, hardy, easy-to-grow perennial. Irises attract butterflies and hummingbirds and make superb cut flowers.

With ~300 species in the genus Iris, the most familiar are tall (28+ inches) bearded irises (Iris germanica). Their distinctive flowers have three outer "falls" and three inner upright "standards." Falls may have fuzzy "beards" or crested ridges. Most bloom in early summer; some bearded hybrids rebloom later.

Planting Irises for Success

• Provide at least half a day of sun and well-drained soil. Insufficient sun = no blooms.
• Prefer fertile, neutral to slightly acidic soil. Sweeten very acidic soil with lime; avoid summer watering to prevent rot.
• Bearded irises need their own bed—don't let other plants shade them.
• Drainage is critical. Loosen soil 12–15 inches deep; mix in 2–4 inches of compost.
• Plant in mid- to late summer.
• Bearded iris rhizomes (fleshy roots) should be partially exposed, or thinly covered in hot climates.
• Plant singly or in groups of three, fans outward, 1–2 feet apart depending on size.
• Dig a shallow 10-inch wide, 4-inch deep hole. Make a soil ridge down the center; place rhizome on ridge, spreading roots down both sides. Fill and firm gently.
• Water thoroughly.
• At planting, top-dress with low-nitrogen fertilizer; repeat in early spring.

Ongoing Care

• Avoid high-nitrogen fertilizers and careless organic mulching—both encourage rhizome rot.
• Keep rhizomes exposed. Unlike bulbs, iris rhizomes need sun and air. Covered or crowded rhizomes rot. Light spring mulch may help.
• Don't trim green leaves—they photosynthesize for next year. Remove brown tips; cut flower stalks to the rhizome to prevent rot.
• If heavy frost hits foliage, remove and destroy it to eliminate borer eggs.
• Every 2–5 years, when clumps congest or lose vigor, divide and replant sound rhizomes in fresh soil. Best time: soon after bloom. Replant where they'll have "wet feet but dry knees."

Pests and Diseases

Irises resist deer and tolerate drought. However, they're susceptible to borers—check rhizomes yearly for holes and discard infested ones. Other potential issues: verbena bud moth, whiteflies, iris weevil, thrips, slugs/snails, aphids, nematodes.

Recommended Varieties

• 'Immortality' – Tall bearded, pure white, reblooms in fall. Zones 4–9.
• Other Zone 4+ rebloomers: 'Feed Back' (dark purple), 'Earl of Essex' (purple), 'I Do' (white).
• Zone 5+: 'Jennifer Rebecca' – lovely mauve-pink.
• Siberian Irises – Distinct from bearded types, available in many colors.

Wit & Wisdom

• The iris is the French royal fleur-de-lis and symbol of Florence, Italy.
• Orris root (from dried Iris 'Florentia' roots) was used for blood/lung ailments; teething babies gnawed dried root "fingers" for natural fluoride.