Rainbow-colored irises, commonly found in Missouri fence rows, ditches and yards, are anything but common, said University of Missouri Extension horticulturist David Trinklein.
A flower of contrasts, iris is hard to kill yet maintains an intricate and delicate beauty.
In Greek mythology, Iris was a golden-winged goddess who traveled on a rainbow. Colorful flowers sprung up wherever she stepped, Trinklein said.
A perennial plant that grows on creeping rhizomes, iris date back more than 3,000 years to the reign of King Thutmose III of Egypt. An avid gardener, the king coveted plants as much as many did gold. He found irises growing abundantly in Syria. After Egypt conquered Syria, he took them to his own gardens.
To the Egyptians, iris symbolized the essence and renewal of life. The three petals represented faith, wisdom and valor. Today, its petals are known as “standards” and stand upright.
In contrast, its three sepals, known as “falls,” droop downward. The shape of the iris inspired the fleur-de-lis emblem, which was widely used on European coats of arms and remains common on flags and in architecture today. European settlers brought irises to Virginia as early as the 1600s.
The most popular garden iris today is the German or bearded iris. Its name comes from the thick, bushy “beards” that appear on the falls of the flower and attract pollinators.
“By careful selection of bearded iris varieties, one can enjoy a remarkable range of colors and a bloom season that extends for weeks,” said Trinklein.
Some bearded irises bloom again in the summer or fall and are classified as “rebloomers.”
Most species grow easily. They need at least eight hours of direct sun per day and a well-drained garden loam. Transplant them at any time, but August to mid-October is preferred, Trinklein said.
Divide clumps when blooming declines. Under normal conditions, divide every three to four years. Reduce the size of the clump by removing several small divisions, leaving part of the clump in the ground, or by digging the entire clump, improving the soil and replanting a few large rhizomes.
Because of their hardiness and beauty, irises are among the most shared plants of gardeners. Relatively few iris are sold in commerce, since most gardeners get them free from their friends and neighbors, Trinklein said.
Irises are propagated vegetatively through division of their fleshy rhizomes. A propagule must have at least one growing point (fan) attached in order to survive.
Expose at least the top third of the rhizome to the sun when planting. Shallow planting is best. Space 12-24 inches apart. Plant closer for more color impact, but these need to be divided in two to three years.
Rhizomes need to be watered immediately after planting. Water established irises less often and avoid overwatering. Deep, occasional watering is preferred over watering frequently.
Irises are heavy feeders. Use a well-balanced fertilizer such as 12-12-12 or 5-10-10 when needed. Avoid fertilizers high in nitrogen because they encourage soft, vegetative growth susceptible to diseases.
A light application of fertilizer in early spring and another a month after blooming is best, Trinklein said. Avoid applying fertilizer directly to exposed rhizomes.
Irises are susceptible to several insect pests. The most troublesome is the iris borer, a moth whose larvae feed on the fleshy rhizome. This allows bacterial soft rot to enter and kill the rhizome. Inspect iris often and discard infected plants. Other common pests include bud moth, iris weevil, thrips, slugs and snails.
Common diseases include bacterial leaf blight and fungal crown rot. Keep the garden free of debris and encourage good air circulation to avoid disease.
Siberian iris has gained popularity with gardeners in recent years. Its blooms are smaller and its foliage is narrower than bearded iris. It prefers cooler weather and a slightly acidic soil. It grows 2-4 feet and is available in a variety of colors. It blooms several weeks later than the bearded iris.
Japanese iris have perhaps the most ornate blooms of any of the irises. They bloom about a month after bearded iris. A bog plant in nature, it prefers wet soils and requires plenty of moisture to produce its showy flowers.