My claim that the iris is an essential part of every perennial flower bed is based on the fact that the 300 plus species of this flower come in such a variety of size and color that there will always be one to suit your requirements. Colors range from white to to nearly black with green, blue, pink and yellow in between. Height varies from a few inches to over three feet so there is no excuse for ignoring this plant. I found an article by Deborah Brown from the University of Minnesota Extension website which is aimed at northern gardeners, but has useful information which applies to all areas.

Few garden flowers have enjoyed the spectacular development and improvement that the iris has in the past fifty years. Today we have thousands of beautiful cultivars of bearded, Siberian and Japanese iris in many colors, sizes and forms. These modern hybrids may require more attention than older types, but in return they offer larger, more numerous flowers and an expanded color range.
There are more than 300 species of iris worldwide; many types are suitable for northern gardens. Most common are the tall bearded iris hybrids with flowering stems over 28 inches high. Shorter bearded iris are also available. Siberian iris are somewhat less common, though they?re actually easier to grow successfully than bearded iris. And for gardeners who like more of a challenge, Japanese iris, which demand special care, might be just the thing to provide an unusual touch of elegance to the garden.

Proper division for replanting. Discard the old central portion of the rhizome. Plant the side “fans” for bloom next year.

Growing Bearded iris

Bearded iris are available in sizes that range from only a few inches (miniature or dwarf) to nearly four feet. The flowers themselves come in almost every color and combination imaginable, from white to near black, bronze to green, blue to nearly red, pink to yellow. They get their name from the fuzzy patch or ?beard? on their down-turned petals or ?falls.? The true petals or ?standards? arch upward to form the center of the ruffled blossoms.

Bearded iris bloom in early to late spring in Minnesota (depending on type), then go into a period of ?summer dormancy? soon afterwards. To prevent seed production, remove flower stems as soon as they?re through blooming, but do not cut back the foliage until it yellows. This allows the plants to store food for the next season of bloom. A few bearded iris may rebloom in fall if left undisturbed, although the late blooms can be touched by early frost.
Like other iris, bearded types are sold as bareroot divisions or as potted plants bearing a cultivar name. A single division of a bearded iris plant will have a thickened rhizome with a ?fan? of leaves at one end and fat roots coming off the rhizome. The best time to plant these divisions is in late summer, from mid-July to Labor Day, when the plants will have time to develop new roots and become established before winter sets in.
Choose a sunny, well-drained site for your iris garden?the sunnier, the better. Make sure standing water does not collect there in spring or after heavy rainfall. Work plenty of compost or peat moss into the soil before planting, and add two pounds of 5-10-10 fertilizer for every 100 square feet of garden.
Dig a shallow hole for each division, leaving a ridge in the center. Place the rhizome over this ridge with the roots spread out on either side. Check the depth to be sure the rhizome is just below the soil surface. In very sandy soil, the rhizome may be planted a little deeper, but no more than one inch below the surface.
Space the rhizomes at least eight inches apart to allow for future growth. When planting several iris of the same variety, arrange them in drifts with the fans pointing in the same direction, bearing in mind that the new plants will come from the fan end and sides of the rhizome. You could also plant rhizomes in a tight circle with the fans pointing outward in a circular clump.
Bearded iris need the same good care that most flowering perennials require: deep watering in dry weather, regular weeding to reduce competition for moisture and nutrients, and fertilizing once or twice each year with 5-10-10 or similar fertilizer. Do not fertilize after mid-August, so plants have time to prepare or ?harden off? before winter.
Summer dormancy provides an opportunity to lift and divide older plants. Established plants need to be divided every third or fourth year or whenever the clumps become crowded and flowering decreases. Use a spading fork to lift the entire clump, being careful not to break the fat feeder roots. Wash off the soil and use a sharp knife to separate the rhizomes into individual fans. Discard the bloomed-out center portions and use only the vigorous healthy fans from the outside of the clump. Cut back the leaves to about six inches and trim off any broken roots. You can label these divisions with the cultivar name and store them for a few weeks in a cool well-ventilated place before planting, if you wish, or you may plant them outdoors immediately.
After the first hard frost in fall, cut back the tops of iris plants to about six inches and clean up any remaining iris debris. Once the ground freezes in November, mulch the bed with four to six inches of loose weed-free compost, straw or leaves. As ice and snow melt in spring, remove the top layer of mulch to allow air and sunlight to dry the surface. Wait a few days before removing the rest of the mulch, taking care not to break the center portion of the fans, where flower buds are developing. Do your final clean-up on a sunny day, after the soil has dried.

See more at University of Minnesota Extension

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