Backyard Gardening
The Irises
By Kathryn Dorman
The irises are blooming! I could not pass up a chance to talk about my favorite flowers. I think irises are so graceful and elegant. The shape of the iris flower is thought to have given rise to the “fleur-de-lis” symbol, which has been used in artistry and architecture for centuries. Irises have been featured in paintings by such famous artists as van Gogh and Monet.
The iris is a perennial, which means the leaves die off in fall, and grow again in spring. ‘Iris’ means rainbow in Greek. Irises come in almost any color, except – for now – true red. The genus Iris belongs to the Iridaceae family, which also includes Crocus and Gladiolus species. About 300 species of iris have been identified worldwide. According to the USDA Forest Service, 28 iris species are native to the United States.
There are three main kinds of irises. Bearded irises (most commonly, Iris germanica), and beardless irises all grow from rhizomes, which are horizontal underground stems. Beardless irises include Japanese (I. ensata), Siberian (I. sibirica), and crested (I. cristata) species. European irises all grow from bulbs, which are compact and highly modified stems. These include Dutch (Iris x hollandica), Spanish (I. xiphium), and English (I. latifolia or I. jacquinii) irises. The leaves of bulbous irises die off right after the blooming season, becoming dormant until the following spring. For the rest of this article, I am going to focus on just the bearded irises.
Iris flower parts occur in sets of three. Three sepals droop downward and are referred to as “falls.” Three petals are more upright, and are called “standards.” These sets of three flower parts are thought by some to represent faith, wisdom, and valor. Some varieties of iris are even bicolored, with one color for the falls and a contrasting color for the standards. Other irises have two different colors within each petal (See Photo 1). As of the last week of May, I counted at least 13 different kinds of bearded iris blooming in my gardens. I couldn’t even fit them all in one picture (See Photo 2)!
The bearded iris has a fuzzy growth, or beard, running down the center of each fall. Different species of bearded iris have evolved to survive different environmental conditions. The American Iris Society recognizes six different classes of bearded iris, based on plant size and flower shape. The dwarf varieties bloom earlier than the taller varieties. Plants range from a few inches to over three feet high. The flowers range from one to ten inches across. Most bearded irises are relatively hardy. They will easily survive our central Pennsylvania winters. Irises can be selected to produce continuous flowering from April through June.
Bearded irises grow best in well-drained, neutral soils. They need at least six hours of direct sunlight. Before blooming, keep soil moist around plants, but not wet. Gently remove weeds around the rhizomes. Mulch should NOT be used on top of rhizomes. Several iris varieties may re-bloom in the fall. (Note: If any of my irises re-bloom this fall, you will read about it in the Renovo Record!)
Irises can be grown from seed, but it is a tricky process. Iris plants can be divided any time the ground isn’t frozen. I dig up my irises while they are blooming, just so I’m sure of their color. Trim each section so it has at least one fan of leaves, a few inches of rhizome, and some roots. Keep only healthy rhizome sections. If the rhizome is soft and smells bad, or if the leaves have brown streaks, discard those portions. Do not use them for composting, as they may be diseased.
Before re-planting, cut the sword-shaped leaves back to one-third their original length. There should be enough leaf surface to maintain photosynthesis, but most of the energy will go toward growing new roots. Plant one to three sections in a clump, spacing clumps about ten inches apart. The rhizome should be just under the soil surface; plant the roots a bit deeper. Firm the soil well, and water thoroughly. Transplanted irises may take a few years to bloom again, but your patience will be rewarded.
After all irises have bloomed, cut each flower stalk to just above the rhizome. This prevents seed pod formation, and promotes vigorous rhizome growth. Do NOT cut the iris leaves until after the first killing frost! They are needed to build up food reserves for the next flowering season. Once the leaves have been frost-killed, remove and destroy any above-ground plant parts. This will help to curb future insect and disease problems. The iris’s main insect pest is the iris borer, a moth whose larvae feed on iris rhizomes. This may lead to bacterial soft rot, the most serious iris disease. Cut out and throw away any diseased rhizomes, and sanitize your pruning shears afterwards.
Poor flowering in irises may be due to cutting leaves too soon, too much shade, or over-fertilization. Don’t let plants get too crowded, weedy, or wet. Irises may benefit from being divided if annual flower production has decreased. Weeds can be controlled by hand pulling. The use of herbicides is not recommended, since it may kill the irises as well as the weeds.
I have been growing bearded irises for over 40 years. They are, for the most part, durable and reliable. You don’t have to dig them up every fall, just to replant in spring. They are deer-resistant and drought-tolerant. They also attract butterflies and hummingbirds. Irises make lovely cut flower bouquets. The iris’s essential oils are used in making perfumes, although some people might develop a sensitivity to some of the chemicals that irises produce. If I bring my irises inside, their strong scent overwhelms me, but I can still look at my irises outside, and enjoy their many colors. They give me a sense of peace and tranquility.
Kathryn Dorman has been a Penn State certified Master Gardener since 2017. She can be reached at clintonmg@psu.edu or through the Clinton County Master Gardener Hotline at (570) 858-0198.
