The Bearded Iris (Iris germanica and its many hybrids) is the most widely recognized and cultivated type of iris. This perennial is distinguished from beardless relatives, such as Siberian or Japanese irises, by the “beard,” a characteristic that defines this group. Extensive hybridization has resulted in a spectrum of colors and patterns.
Defining Physical Characteristics
The structure of the Bearded Iris flower consists of six distinct petal-like segments arranged in two layers. The three upright segments are called the Standards, which typically arch inward toward the center of the bloom. Below them are the three lower, often cascading, segments known as the Falls.
Running down the center of each Fall is the namesake feature: the beard. This is a thick, fuzzy line of short, hair-like filaments that strongly resembles a small caterpillar. The beard can be the same color as the falls or a contrasting shade, and it serves to guide pollinators toward the reproductive parts of the flower.
Within the flower’s throat, nestled above the beard, are three smaller, upright structures called the Style Arms. The entire plant grows from a rhizome, a food storage organ generally located right at the soil surface. This surface location heavily influences successful cultivation. The foliage forms a fan of broad, sword-like, blue-green leaves.
Understanding Size Classifications
The numerous hybrids within the Bearded Iris group are organized into a horticultural classification system based primarily on their mature height and bloom time. This system helps gardeners select appropriate varieties for specific landscape placements and ensures a continuous display of blooms throughout the season.
Classification Classes
The classes are generally grouped by height and bloom time:
- Miniature Dwarf Bearded (MDB): Reaches a maximum height of 20 centimeters (8 inches) and is the earliest to flower.
- Standard Dwarf Bearded (SDB): Grows between 21 and 40 centimeters (8 to 16 inches) tall, ideal for the front of a garden border.
- Intermediate Bearded (IB): Ranges from 41 to 70 centimeters (16 to 27.5 inches), bridging the bloom period between dwarfs and the tallest varieties.
- Border Bearded (BB): Shares the same height range as IBs but has proportionally smaller blooms and flowers simultaneously with the largest class.
- Tall Bearded (TB): Stands over 70 centimeters (27.5 inches) high and is typically the last to bloom, providing a stately focal point.
Essential Growing Requirements
Successful cultivation of Bearded Irises depends heavily on providing the correct environmental conditions, which are notably different from many common perennials. The primary factor is sunlight, as the plants require at least six hours of direct sun daily to produce a vigorous display of flowers. Insufficient light exposure often results in the plant producing only foliage, a condition sometimes referred to as “going blind.”
Excellent soil drainage is required, as the fleshy rhizomes are highly susceptible to rot in soggy conditions. Planting on a slope or incorporating coarse sand or gypsum can significantly improve drainage in heavy clay areas. The ideal planting time is late summer to early fall, allowing roots to establish for six weeks before the first hard frost.
When planting, the rhizome must be positioned so its top surface is exposed or only barely covered by soil. Planting the rhizome too deeply is a common error that can prevent flowering and encourage soft rot. In regions with hot summers, covering the rhizome with a thin layer (up to one inch of soil) can offer protection. Once established, Bearded Irises are drought-tolerant and require minimal supplemental water, but newly planted rhizomes should be watered consistently until their root systems are developed.
Long-Term Maintenance and Division
To maintain vigorous flowering and prevent overcrowding, Bearded Iris clumps require division every three to five years. As the plants multiply, the older, original rhizomes in the center of the clump can become depleted, leading to a noticeable reduction in bloom quantity and a dense, unproductive mat of foliage. The best time to perform this division is in mid-to-late summer, shortly after the blooming period concludes, which allows the newly separated sections enough time to re-establish roots before winter.
When dividing, the entire clump is dug up, and the healthy outer rhizomes with a fan of leaves are retained for replanting. The older, spent sections in the center should be discarded, as they are less productive. The foliage of the divisions is often trimmed back to about six inches to reduce stress on the transplant and aid in re-establishment.
General maintenance includes removing the spent flower stalks, or deadheading, by cutting the stalk down to the foliage after all blooms have faded. In the fall, clearing away old, dead, or diseased foliage prevents the overwintering of pests, such as the iris borer, and reduces the risk of fungal diseases. Keeping the planting area free of debris and avoiding mulch around the rhizome helps ensure adequate air circulation and sunlight exposure.