Irises: Planting, Growing, and Care for Rainbow Goddesses

BA Elliott

The tall, beautiful iris, named for the Greek goddess who rode rainbows, comes in many magical colors.

Every gardener wants this perennial. Despite divine origins, it's hardy, reliable, and easy to grow. Irises attract butterflies and hummingbirds and make lovely cut flowers.

Some 300 species exist in the genus Iris. The most familiar are tall (28+ inches) bearded irises (Iris germanica).

Distinctive flowers have three large outer petals ("falls") and three inner upright petals ("standards"). Falls may have beards or crests. Bearded irises have soft hairs along the falls' centers; crested irises form a comb or ridge.

Most bloom in early summer. Some bearded hybrids are remontant, flowering again later in summer.

Planting Irises

• Irises need at least half a day of sun and well-drained soil. Without sufficient sun, they won't bloom.
• They prefer fertile, neutral to slightly acidic soil. If very acidic, add lime and avoid summer watering (causes rot).
• Bearded irises must not be shaded by other plants; many thrive in dedicated beds.
• Drainage is crucial. Loosen soil 12–15 inches deep, then 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 rhizomes singly or in groups of three with fans outermost, 1–2 feet apart depending on size.
• Dig a shallow hole 10 inches wide, 4 inches deep. Make a soil ridge down the center, place rhizome on ridge with roots spreading down both sides. Fill and firm gently.
• Water thoroughly.
• At planting, top-dress with low-nitrogen fertilizer; repeat in early spring.

Care and Maintenance

• Avoid high-nitrogen fertilizers on the surface or careless organic mulching, which encourages rhizome rot.
• Keep rhizomes exposed. Unlike bulbs, iris rhizomes need sun and air to dry out. Covered or crowded rhizomes rot. Shallow spring mulching may help.
• Don't trim iris leaves—they photosynthesize for next year's growth. Cut brown tips and cut flowering stalks to the rhizome to discourage 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 are deer-resistant and drought-tolerant but susceptible to borers—check rhizomes yearly for holes, discarding infested ones.

Verbena bud moth, whiteflies, iris weevil, thrips, slugs/snails, aphids, and nematodes may also trouble plants.

Recommended Varieties

• 'Immortality' — tall bearded, pure white flowers, reblooms in fall. Zones 4–9.
• Other rebloomers hardy to Zone 4: 'Feed Back' (dark purple), 'Earl of Essex' (purple), 'I Do' (white).
• Zone 5+: 'Jennifer Rebecca' — mauve pink beauty.
• Siberian Irises — range of colors, distinct from bearded types.

Wit & Wisdom

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