Anatomy of an Iris

Parts of an Iris

An iris is composed of distinct floral and vegetative structures, each playing an important role in the plant’s growth, reproduction, and appearance.

Flower Parts

Standards
The upright petals at the top of the bloom. Standards often provide contrast in color or tone and help define many classic iris color patterns.
Falls
The three downward-arching petals beneath the standards. Falls typically display the most dramatic color, markings, veining, or patterning on the flower.
Beard (bearded irises)
A soft, fuzzy strip of hairs located along the center of each fall. The beard often contrasts in color and serves as a visual and physical guide for pollinators.
Style Arms
Petal-like structures that arch over the falls. They protect the reproductive organs and are often mistaken for petals.
Stigma
Located beneath the tip of each style arm, the stigma receives pollen during fertilization.
Anthers
Structures that produce and release pollen, typically found beneath the style arms.

Stem, Buds, and Protective Structures

Stalk (Flower Stem)
The vertical stem that supports the bloom and developing buds.
Spathe
A protective, leaf-like sheath that encloses the developing iris bud before it opens. As the bud matures, the spathe splits or opens to allow the flower to emerge and often dries to a papery texture after bloom.
Bud
An unopened flower enclosed within the spathe. Multiple buds may form along a single stalk, allowing for sequential blooming.
Spent Bloom
A flower that has finished blooming and is beginning to fade or dry.

Foliage and Growth

Leaves (Fans)
Sword-shaped leaves that grow in a fan arrangement from the rhizome. Each fan represents a growth point capable of producing blooms.
Rhizome
A thick, horizontal underground stem from which leaves, roots, and new growth emerge. Rhizomes store energy and allow irises to spread and multiply.
Roots
Fibrous structures extending from the underside of the rhizome that anchor the plant and absorb water and nutrients.

When & Why to Divide Bearded Irises

Why Irises Need to Be Divided

Bearded irises grow outward from a central point, producing new rhizomes each year. Over time, this natural growth cycle causes the planting to become crowded, which can reduce bloom performance and plant health.

Dividing irises:

Restores vigorous blooming
Prevents overcrowding and rot
Encourages new growth and increase
Helps manage disease and pests
Keeps named cultivars true and healthy

When to Divide

The ideal time to divide bearded irises is:

Mid-summer to early fall, typically 4–8 weeks after bloom.

At this stage:

Blooming has finished
New rhizomes (“pups”) are mature enough to replant
The plant still has time to establish roots before winter

Avoid dividing:

During active bloom
Late fall in cold climates (insufficient root establishment)
Early spring (reduces bloom for that season)

Signs an Iris Should Be Divided

Common indicators include:

Fewer or no blooms despite healthy foliage
Dense clumps with rhizomes stacked or overlapping
Dead or shriveled rhizomes in the center of the clump
Soft or rotting rhizomes
Fans growing away from the center, leaving a bare middle
Increased disease or pest pressure
Rhizomes pushing above soil level

These are normal signals — not failure — that the plant has reached the point where division is beneficial.

Understanding the Mother Rhizome

The mother rhizome is the original rhizome that produced the current season’s bloom.

Important points:

A mother rhizome blooms only once
After blooming, it redirects energy into producing new rhizomes (often called pups)
The mother rhizome is not dead — it serves as a nutrient source during the growth of new fans and the source of additional increases. It can continue to produce increases

Should the mother rhizome be discarded?

Not immediately.

Best practice:

Keep the mother rhizome attached while dividing.
Once new rhizomes are separated and established, the old rhizome can be trimmed away if it is:
- Soft
- Hollow
- Diseased
- Fully spent

Healthy mother rhizomes can temporarily support young divisions and should not be removed prematurely. They may continue to produce increases depending on the cultivar for months to even a year after bloom. Frequently, the mother rhizome will just return to the earth to feed ground.

What to Keep When Dividing

Each good division should include:

A healthy fan of leaves
A firm, disease-free rhizome
Visible roots or root nubs

Large fans may be trimmed back to 6–8 inches to reduce wind stress and transplant shock.

Why Division Improves Bloom

Bearded irises bloom on new, vigorous rhizomes, not exhausted ones. Division:

Resets spacing
Improves air flow
Directs energy into fresh growth
Mimics the plant’s natural outward expansion

Think of division not as disruption — but as renewal.