Iris Flowers: Types, Planting, Care, and Solving Rot & Borer Problems

Iris inspire passionate devotees—societies, bulletins, and dedicated growers like Kelly D. Norris, farm manager of Rainbow Iris Farm. "They come in every color of the rainbow, in every permutation. For hardy outdoor plants with this much color range, irises are unmatched." Yet they're often misunderstood. Here's what you need to know.

Types: Bearded vs. Beardless

325 species, 50,000+ varieties fall into two main groups. Bearded irises have a fuzzy "beard" on falls; beardless (Japanese, Siberian) have "signals." The difference goes deeper:

• Bearded: Need constant drainage; tolerate heavy soil if it drains. Excellent xeriscape plants—drought-tolerant, adaptable from Nantucket to Tucson. Subdivided into six size classes; dwarfs dislike overhead competition.
• Beardless: Grassier foliage. Siberians tolerate more shade and competition. Japanese irises need acidic soil, no standing water. Virginia irises love moisture. Crested irises thrive in dry shade. ~1,000 new varieties yearly.

Planting and Care

All irises (except Juno) grow from rhizomes—modified stems at or just below soil surface, not true bulbs.

• Bearded: Plant shallow. Loamy/clay: barely cover. Light soil/hot climates: up to 1.5 inches deep. Avoid excess moisture (rot/borers) but insulate from sunburn.
• Beardless: Rhizomes look different—knobby fingers vs. tubers.
• Dividing: Beardless: every 3–7 years (Siberians slower to establish). Bearded: every 3–5 years, some annually. Dig, break into smallest viable chunks, replant or share.

Major Problems: Soft Rot and Borers

Soft rot: Bacterial, mushy rhizomes with foul smell. Caused by excess moisture around crown. Solution: Dig, divide, dip pieces in 50% bleach/50% water for up to an hour. Replant in better-drained spot.

Borers: Eastern 2/3 of U.S. Prevention is best: Clean beds spring and fall; don't mulch heavily over rhizomes. Debris creates moth egg-laying sites. "Give your irises breathing room."

See different iris varieties.