German Bearded Iris

Worldwide, there exist over 280 species in the genus Iris (family = Iridaceae). Of those, 28 are native to the United States, but only four are native to Pennsylvania. Harlequin blue flag iris (Iris versicolor) and Shreve’s iris (Iris virginiana L. var. shrevei) are found in Pennsylvania in wet areas along creeks and lakes and in boggy areas. Crested iris (Iris cristata) and the upland dwarf violet iris (Iris verna var. smalliana) are at home here in semi-shaded woodlands and their slopes. While these natives are important ecologically, most gardeners are more familiar with cultivars of the German bearded iris, a native of the Mediterranean region of southern Europe. In fact, the straight species Iris germanica can rarely be found in commerce today, but it has been such a beloved flower that there are thousands of cultivars from which to choose.

The German bearded iris (Iris x germanica) is also known as German iris, bearded iris, rhizomatous iris, and common flag. It is an herbaceous perennial flower that thrives from USDA hardiness zones 3 to 10. This iris is an old-fashioned and beloved pass-along plant.

Rhizomes can be purchased bare root from many online sources and some garden centers for late summer planting. Potted irises can be found in garden centers and planted from the pot into the ground after purchase.

German bearded iris roots and semi-evergreen leaves emerge from thick underground stems called rhizomes. This plant’s green, strap-like leaves are linear and lanceolate with entire margins. Depending on the cultivar, they are 1 to 3 inches wide and more than 6 inches tall. The leaf arrangement is technically called rosulate, as it overlaps at the base and emerges as a fan, oriented in one plane. Most cultivars flower in spring, though a relatively recent effort has produced many which rebloom. The flower stalk emerges from and is held above the fan of leaves. The leafless flower stalk can have from one to as many a dozen flowers along the stalk, blooming sequentially, with each lasting three to five days.

The glory of this plant lies in its unique, stunning, and recognizable flower. Each flower has six petals: three are “falls” that spread outward or downward from the center, and three are the inner erect “standards.” The petals vary from fairly flat and smooth to those with quite frilly edges. Along the center rib of each of the falls lies a fuzzy, colorful band called the “beard.”

Iris was the Greek goddess of the rainbow. It is an apt name for this flower as it comes in all colors of the rainbow, from pink, maroon, reddish, orange, yellow, green, blue, violet, deep purple, brown, white, and black. Some cultivars sport only one color (“selfs”) and are stunning in their own right. But the magic arises with the myriad of combinations of colors of the falls and the standards and how those petals can be accentuated by the colorful beard.

Siting and Planting

This iris prefers a site in full sun. Partial shade is an option, but flowering will suffer. The rhizome must be planted in an area with good drainage as it will more likely succumb to root rot and other problems if it stays wet. Amend the planting area with organic matter before planting, if necessary. Dig a hole 4 to 6 inches deep and mound the soil in the center of the hole. Place the rhizome on top of the mound with its roots extending down the sides of the mound. Cover the rhizome with soil so that the top of the rhizome is just below or at ground level. With this iris, it is better to be too shallow than too deep. Plant single varieties in uneven numbers, 12 to 18 inches apart, pointing the fan of leaves away from the center of the clump. 

Maintenance

German bearded iris is relatively carefree. Fertilize with ½ cup of 5-10-10 around each clump (not on top of the rhizomes) after flowering. Remove the flower stalk after the last flower fades to discourage the energy expenditure of seed development. In late fall, remove the spent leaves by cutting to a height of 3 to 6 inches. Once established, the German iris is drought-tolerant. Water the new plantings and during dry spells. Avoid mulching on top of the rhizomes.

Each year more “offsets” or rhizomes develop. After three to five years, the clump must be gently dug, divided, and replanted. Late summer is the ideal time for this process. Trim the leaves by 2/3. With a garden spade, remove the clump carefully. Pull apart the rhizomes by hand. Sometimes cutting with a sanitized knife is warranted. Toss any old or soft rhizomes. Plant the remaining irises or pass them along to a gardening friend. 

Diseases and Pests

Bacterial soft rot is the most common disease of this flower. By meeting its cultural requirements—good drainage, planting close to the surface, and minimal mulching—the incidence of bacterial soft rot is minimized. Infected plants smell absolutely awful. Remove the entire plant and bag, and toss them out with the garbage. Do not compost. Cleaning the bed at the end of the season as well as dividing the clump before it gets too crowded, also helps prevent infection.

A most serious pest of the rhizome is the iris borer. After hatching on the leaves, these caterpillars tunnel through the leaves and into the rhizome, leaving holes predisposing the plant to bacterial soft rot. Indications of infestation include dying brown leaf tips, water-soaked steaks on the leaves, an accumulation of sawdust-like frass at the base of the leaves, and, later, holes in the rhizome itself. The leaf can be crushed early in the season with the small caterpillar inside. Inspect for damage in mid-summer, and dig up and bag any rhizomes with holes or borers. Clean up debris around the iris clump in the fall after a hard frost when the female moths have finished laying eggs.  

For more information on the diseases of iris, see this Penn State Extension article on iris diseases.

Categories of the German Bearded Iris

German bearded irises are categorized by height and flower size. Generally, the shorter the iris, the earlier it blooms, yet variations in bloom time exist within categories.

• Miniature dwarf – height of up to 8, with 1 to 2-inch diameter flowers
• Standard dwarf – height of 8 to 15 inches
• Intermediate – height of 16 to 27 inches
• Miniature tall – height of 16 to 25 inches, with small flowers
• Border – height of 16 to 27 inches
• Tall – height of 28 to 38 inches

They are also categorized by the color patterns and combinations:

• Amoena – white standards and colored falls
• Bicolor – standards and falls of contrasting colors
• Bitone – standards and falls in different shades of the same color
• Blend – two or more colors that are overlaid, mixed, or swirled into each other
• Luminata – white or yellow hafts (the area on the fall at either side of the beard), with the remaining area on the petals being washed with white veins
• Neglecta – bitone iris in blue or purple shades
• Plicata – dotted, stitched, or stippled falls over a lighter ground color
• Self – same color standards and falls
• Variegata – yellow standards and darker falls of brown, red, or purple.
• Zonal – a white or lightened area around the beard

Use in the Garden

German bearded irises can find a home in every garden. Variations in height allow placement in the front or middle of a mixed border planting. Color variations easily allow for incorporation into existing planting schemes. It is just as useful in the cottage garden as in formal planting. They are beautiful enough to be the focal point. Plant them around a sculpture. Place dwarf species in a container by the front door. Add cultivars to a cutting garden, as German bearded irises make great cut flowers. They can also be a welcome addition to pollinator-friendly planting. The pollen is easily found by bees—they land on the falls and climb through the beard to get to the pollen at the center of the flower.

When you decide to add German bearded irises to your garden, the biggest problem you may encounter with this beauty is knowing when to stop!