The World of Irises

By Sherrie Eoff

 There are about 300 species in the Genus Iridaceae, which include the Bearded, Dutch, Siberian, Japanese, and the Louisianna iris. It takes its name from the Greek word for a rainbow, which is also the name for the Greek goddess of the rainbow, Iris. 

  The iris that is most familiar is the Bearded Iris (Iris germanica). To me it is the old fashion iris that my grandmother and mother grew. They come in a rainbow of colors and in different heights; dwarft, intermediate, and tall. They are also called “flags” and German iris. Bearded are spring blooming perennials that flourish in zones 3-9 and are easy to grow. Some have a wonderful fragrance. Hybridizing has diminished fragrance but the size of the blooms has increased.  The dwarf bearded iris start the season, blooming in April, with the tall beardeds blooming May-June.  Beardeds grow from a rhizome. They should be planted in full sun and watered only when extremely dry or after transplanting. fertilize in spring and just after blooming with a low-nitrogen fertilizer. They need good air circulation and do not mulch. prune back foliage in fall and divide every 3-4 years. DO NOT plant the rhizome too deep.  A bit of the rhizome should be just visible at the soil surface. If the rhizome is planted too deep, it will not bloom. Irises are deer-resistant and drought-tolerant.

Bearded Iris

  Dutch iris, also known as Iris hollandica, have orchid-like flowers with silky petals. Flower colors range from pale blue and lemon through deep purple, bronze, rose and gold. It has a slender stem in spring, topped by gloriously colored flowers. Bulbs are planted in the fall; the leaves emerge in the spring followed by the uniquely shaped iris blossom . The long stems make great cut flowers. Full sun and moist well drained soil is required. Zones 5-9. Permit foliage to “ripen” naturally so food can be manufactured by the leaves to nourish and enlarge the bulbs. Once the foliage browns it may be cut away. I call these the refined cousin to the Bearded iris. Dutch iris comes in dwarf and tall also. Dwarf  being only about 4-6” and bloom very early spring. Tall are 20-35” and bloom in late spring-early summer (May).

Dutch Iris

Siberian Iris (Iris sibirica) are the second most common iris in the garden. They are the dainty cousin to the Dutch and Bearded Iris.  Hardy and easy to grow, this perennial is smaller and more delicate then its cousins. It does not have the fuzzy beard that the bearded iris has. Siberian comes in shades of blue, purple, pink, white, yellow, and wine-red. The foliage is upright and grass like, and flowers blossom on tall stems in late May and June.  They prefer moist, well drained soil, with full-part sun.  Siberians may be planted in spring or late summer.  For the best visual display, plant in groups of  3-5.  Siberian also grows from a rhizome, but should be planted deeper than bearded iris.  Plant each rhizome so that it is covered with 1-2” of soil. It may take 3-4 years after planted for them to bloom. They are a good choice for naturalizing around a pond or water feature.  Grows 18-24” in some varieties and 2-4’ tall in others. Yellow Flag iris is 2-4’ and is considered invasive by some. 

Fertilize in early spring and immediately after blooming with 10-10-10 fertilizer. Mulch heavily in winter.  Cut back dead leaves and stalks in late fall or early spring. 

Siberian Iris

Japanese Iris (Iris ensata) require a lot of water and may require significant care. But you will be rewarded with large beautiful plants and robust blooms. If planted near a pond they will do just fine on their own.  Japanese should be grown in loose, well aerated, and nutrient rich organic matter. They are heavy feeders. A fertilizer for acid loving plants will be well received by the Japanese iris. 2 applications during the growing season are best. Rhizome clumps should be divided every few years and best done in spring or early fall.  After blooming season cut off faded flowers and stems to ensure beautiful blooms for next season. Bloom is “flat” in shape.

Japanese Iris

Louisiana Iris is a native plant to Louisiana that is happy in swamps or your pond or bog garden. They love wet feet. . It is an early spring bloomer in subtropical climates, June in the north. Comes in a multitude of colors and multiplies each year. Hardy to zone 5.  24-36” tall. It has fan shaped strap leaves and is somewhat invasive.  Common color is yellow but does come in dark purple to light blue. Leaves add great shape and texture to garden. Cut back each fall. To divide, simply dig iris in fall and separate corms. Fertilize lightly with an all purpose 15-15-15 fertilizer in spring, before flowering. 

Louisiana Iris

The diminutive Crested Iris (Iris cristata)  grows from a rhizome and is native to Arkansas. It will grow best in moist, humus-rich soil in full-part sun. Blooms in mid-late spring and flowers are 1-1/4-4” in size. It is a dainty, frilly bloom in shades of blues, violet, or white. They have a crest or ridge on each fall instead of a beard.

Crested Iris

Iris Reticulata is grown from a bulb and is fragrant.  It blooms in early spring in a variety of colors and is only about 4-6” tall. Hardy in zone 5-9.  Plant in full sun to part shade. It has a central yellow mark on each fall. Cute as can be and a sure sign of spring! 

Iris Reticulata

Japanese Roof Iris (Iris tectorum)  is native to China but was found growing on roofs in Japan, hence the name. It grows about a foot tall with a spreading, rhizomatous habit common to most irises. Leaves are light green, about a foot long, sword shaped with a slightly corrugated texture down the length. The leaves do not stand erect, but arch over, making them a graceful groundcover. Flowers appear in late April and early May. 4” flowers come in white and lavender. Roof Iris were grown on the roofs in Japan, when during wartime, a decree was issued by the Emperor that made it illegal to waste land growing flowers.  All available land had to be used for rice or vegetables. The main reason for growing the iris was for the white powder that was made by grinding the roots. This powder was used to make the makeup that created the white faces of the Geisha girls. Roof iris grows as well in shade as in sun. Rhizomes should be just at surface of the soil. 

Japanese Roof Iris

  Iris spuria, commonly called salt marsh iris or butterfly iris, is a tall, rhizomatous, beardless iris.  Developed around the turn of the century in England, it has the ability to compete with other plants and grows well in dry soil! Grows from a rhizome with stems  20-40” tall with 1-3 blooms per stem. Plants will tolerate light shade. Blooms will remind you of the Dutch Iris. Colors range in white, yellow, orange, copper, brown, blue, lavender, and purple. It flowers after the Bearded Iris. Hardy zones 5-9.

Iris Spuria