Irises: A Varied Plant Family
by Jeanne Rose, UC Master Gardener

The Iris family is large and remarkably diverse with 200-300 species. Flower color, form, culture, and blooming seasons vary. Irises grow from either rhizomes or bulbs. Their leaves are sword-shaped, flowers are complex, and many are fragrant. Most bloom in spring or early summer.

All iris flowers are comprised of three inner and three outer segments. The inner segments are called "standards" and are erect or arching petals. The three outer segments are called "falls" and these petal-like structures (sepals) are held at various angles, from nearly horizontal to drooping.

There are three categories of iris: bearded - named for the caterpillar-like structures on the falls; beardless - the falls are smooth; and crested - each fall bears a comb-like ridge instead of a beard. Bearded irises are widely available through nurseries, catalogs, and specialty growers. Fewer sources offer beardless irises and other iris species.

Bearded Iris: All bearded irises grow from rhizomes. The color range seems endless. Many are bicolored with the standards of one color and the falls of another; others are splashed or striped with contrasting colors. Most of us are familiar with the tall (2-4 feet) bearded iris common in local gardens. But also available are miniature dwarf (8 inches tall), standard dwarf (8-15 inches), intermediate (15-28 inches), border (15-28 inches) and miniature tall (18-28 inches).

Tall bearded irises are the easiest to grow of the iris family. They need very little water and grow best in full sun, but also tolerate light shade. Tall bearded irises used to bloom only in the spring but, thanks to modern-day hybridizers, we now have reblooming iris, some of which are almost everblooming in mild climates.

Beardless Iris: The beardless iris flowers are considerably different in appearance from one species to another. The rhizomes have fibrous roots and need more moisture than beardeds. The most widely sold beardless irises suitable for our area are the Japanese, Louisiana, Pacific Coast, and Siberian.

The blooms of Japanese irises are essentially flat. The "singles" have three broad falls and reduced standards and present a somewhat triangular flower outline. The "doubles" have standards marked like the falls and about the same size and shape, resulting in a circular flower outline. The plants have graceful, upright leaves with raised midribs. The best uses for the Japanese irises are moist borders, at the edge of pools or streams, or in boxes or pots plunged halfway to the rim in a pond or pool during the growing season.

The Louisiana irises or swamp irises include a few species from the Gulf Coast region. The blossoms are borne on 2-5 foot stems among and above long, narrow, unribbed leaves. These require lots of water, neutral to acid soil, and light afternoon shade when summer heat is intense.

The Pacific Coast iris group includes eleven species native to the Pacific Coast. From these breeders have developed hybrids in a range of bloom colors and patterns. Foliage is narrow and clumps are like coarse grass. Slender flower stems reach 8-24 inches. These irises are best in sun to light shade in well-drained soil, with moderate to scant water in summer.

Siberian irises are native to Europe and Asia. They grow in clumps of narrow, grasslike leaves, are deciduous in winter, and produce slender tall stems bearing 2-5 blossoms with upright standards and flaring to drooping falls. In our hot summers these plants need partial or dappled shade and neutral to acid soil.

Bulbous Irises: Three types of bulb irises are suitable for our area. Dutch irises are used in the floral industry. The flowers are borne in spring atop slender stems rising from very narrow foliage. The standards are narrow and upright; the falls project downward and may be oval to circular. Spanish irises are similar to Dutch irises but have smaller flowers and bloom a couple weeks later.

Reticulata irises are classic rock-garden and container plants. The flowers are like small Dutch irises and appear on 6-8 inch stems in mid-winter or early spring. The narrow blue-green leaves appear after bloom. They need regular moisture fall through spring and should be kept dry during the summer dormant period.

I've mentioned only some of the irises suited to our area. Try introducing some of these and other members of the iris family to your garden.

May 15, 2003