Bearded Irises are among the easiest and hardiest perennials to grow, blooming year after year with little attention. Named after Iris, the Greek goddess of the rainbow, they are available in almost all colors except true red. There is a whole range of colors, sizes and forms available that can give you a succession of blooms from mid-April to early July.
Are there different types of Irises? Irises are divided into four main groups: bulbous, crested, beardless, and bearded Iris. Of the hundreds of Irises available bearded Iris are the most
popular and spectacular. Bearded Iris share a common characteristic of fuzzy beards on their falls.
Where can I grow them? Bearded Irises are usually planted in garden beds along with annuals and other perennials. They will grow best if they are sited in well-drained, neutral (7.0 pH) soil and receive lots of sun.
When should I plant iris? Bearded Irises are best planted in mid-to late August. If you are planting them in September keep in mind the later you plant the less likely you are to have blooms the first season. If you are using iris rhizomes that are dry soak them in warm water for a few hours before planting. Irises that are growing in a pot can be transplanted at any time. Just slip the soil, root system, and plant from the pot to the soil being careful not to plant the iris rhizome too deeply. You should be able to see the top of the rhizome after planting.
Should I plant them alone or in groups? Planting in clumps is more effective that planting them alone. If planting several of one variety space them six inches apart in a circle with the growing elbows facing outward and spacing between clumps of 2-3 feet.
Do Irises need mulch during the growing season? No – covering the rhizomes with soil or organic materials at this time promotes rhizome rot.
What about dividing Iris? Healthy iris plants should be divided every third or fourth year. The rhizomes branch like a fork and grow outward from the back of the fan of leaves. Dig the plants with a spading fork and gently pull apart the divisions. Cut back the foliage to about six inches. Examine the rhizomes carefully for signs of problems, such as rot or borers, keeping only healthy rhizomes. Generally the vigorous portions are the younger parts of the clump. Place the rhizomes on top of a ridge of soil and spread out the roots. Cover with soil making sure the rhizome is partially exposed. When the soil has been firmed and the plant watered the rhizome should be half-exposed out of the soil.
Why won’t my Irises bloom? Lack of sun, too much nitrogen, and planting too deeply are the most common factors that keep your irises from blooming well. Often it is a combination of these factors. It isn’t unusual at all to have properly sited and planted a bed of irises years ago but over time the conditions change. As surrounding plant material grows it provides more shade and mulch tends to build up on top of the rhizomes. If this has happened just dig and reset the irises. Applying fertilizers high in nitrogen (such as lawn fertilizers) in the immediate area will result in lush growth with few blooms.
What about iris borer? One of the few problems to bother irises is the iris borer. This insect begins as eggs lay late in fall on iris foliage and rhizomes. In spring the next stage burrows into the foliage and rhizomes and develops through the summer into a gray wormlike creature around an inch in length. In early summer you might be able to see tracings where they are traveling around inside the leaves. By mid-summer the borers are in the rhizomes. In late summer the borers leave the irises and pupate in the soil until fall when they hatch into a small indistinct moth that starts the cycle over again by laying new eggs on the irises. The foliage on irises that is affected by iris borers will have yellow and brown edges and the rhizomes will have holes chewed through them.
What should I do if I suspect my irises have borers? Whenever you find evidence of borers it is important that you dig the rhizomes and examine them, replanting only those that are healthy. The chemical that has proven to be the most effective against borers is Cygon, a systemic insecticide, however, Cygon has been taken off the market and there is no other chemical that is labeled to be used on Iris to control Iris bore. University studies have shown positive results in controlling Iris bore by beneficial nematodes. The best species of nematodes is one called Steinernema carpocapsae showing nearly 100% control of borers is used properly. Soil temperature needs to be above 50°F, also applying 1 quart of water per square foot so the nematodes can swim to their prey.
How should I fertilize irises? Bearded irises are not heavy feeders and will do well with a yearly spring application of a fertilizer with 10-10-10 or 10-20-10.
There are a variety of irises available and the will add a great amount of color to any landscape. Please ask a professional at McShane’s Nursery and Landscape Supply to find the variety right for you and your landscape. They are always eager to help!