How to Grow and Divide Bearded Irises

Bearded irises are a popular garden perennial, known for their vibrant blooms and relative ease of care. While they thrive with minimal attention, dividing overcrowded irises ensures continued healthy growth and abundant flowering. This guide provides comprehensive instructions on growing and dividing bearded irises, empowering you to cultivate a flourishing iris garden.

Understanding Bearded Irises

Bearded irises, often called German irises (Iris x germanica), are prized for their distinctive flowers. Each bloom boasts three upright petals (standards) and three drooping petals (falls), with a characteristic “beard” of fuzzy hairs on each fall. These hardy perennials thrive in USDA Plant Hardiness Zones 3 through 9 and offer a vast array of colors and bicolors. They typically bloom in mid-to-late spring, though reblooming varieties extend the floral display. The American Iris Society categorizes bearded irises by height, ranging from miniature varieties to those reaching nearly three feet tall.

Planting Bearded Irises

The optimal time for planting bearded irises is from July to September, or in spring if using potted plants. Select a location with well-drained soil and full sun exposure. Bearded irises grow from rhizomes, fleshy underground stems susceptible to rot in excessively moist conditions.

Before planting, prepare the soil by loosening it and removing any weeds. Amend heavy clay soils with sand to improve drainage. Plant the rhizome horizontally, just beneath the soil surface, ensuring the roots are buried. Avoid covering the rhizome with mulch to prevent rot.

Caring for Bearded Irises

Fertilizing

Established irises generally require minimal fertilization. If your soil is nutrient-poor, incorporate a balanced granular fertilizer during bed preparation.

Watering

Once established, bearded irises are drought-tolerant and rarely need supplemental watering. Water thoroughly after planting, but avoid waterlogged conditions.

Deadheading

After flowering, remove spent flower stalks to redirect the plant’s energy towards rhizome development rather than seed production. This practice promotes stronger growth and future blooms.

Pest and Disease Management

Iris borers are the primary pest affecting bearded irises. Inspect plants regularly for signs of infestation, such as brown streaks on foliage or holes chewed in leaves. Crush borers found on leaves or remove affected foliage. For rhizome infestations, dig up and discard the affected rhizomes. To prevent overwintering, remove and dispose of all foliage after the first frost.

Dividing Bearded Irises

Overcrowding diminishes iris vigor and flowering. Divide irises every two to three years, ideally in July or August, about a month after blooming.

  1. Digging: Carefully excavate the entire clump, preserving the root system.

  2. Separating: Gently separate the rhizomes, ensuring each division has at least one “fan” of leaves and attached roots.

  3. Trimming: Cut back the foliage to approximately six to eight inches.

  4. Replanting: Replant the healthy divisions, discarding any old or damaged rhizomes. Space the new plants according to their mature size. Share extra rhizomes with fellow gardeners!

Conclusion

By following these guidelines, you can successfully grow and divide bearded irises, adding beauty and elegance to your garden. With proper care and timely division, your irises will reward you with abundant blooms for years to come. Enjoy the vibrant colors and unique charm of these remarkable perennials!