Bearded irises have come a long way from the simple Iris pallida -- sometimes fondly called "Grandma's flags" -- that were grown in so many gardens 60 or more years ago. One of the least demanding of all plants, irises are undergoing a radical transformation regarding color, flower form, and reblooming abilities.
I fell in love with reblooming bearded irises five years ago while experimenting with companion plants for my roses. I garden in the benevolent climate of Southern California, where long periods of sunshine contribute to spectacular growth of almost any plant. I have a modest property -- 48 feet by 150 feet -- and my dwelling and garage have first claim on the land. So when I sacrifice prized garden space, the plant must be a prolific performer. My bearded irises did not disappoint.
A small group of iris fanciers have been tracking the development of bearded irises with reblooming characteristics (also called "remontant"). Jeanne Plank, treasurer of the American Iris Society, introduced me to the pleasures of 2 1/2- to 4-foot-tall bearded irises as a way of adding vertical color and sculptural leaf form to a garden landscape. When I told her I didn't want a plant that blooms for just two or three weeks a year, she swept away all my objections by educating me about reblooming irises.
These extra-vigorous plants bloom in spring, often a week or so earlier than standard bearded irises, and the good news is that they'll bloom again in summer, and again in fall. In warm, dry climates, some will bloom four or five times annually.
Bearded irises grow from rhizomes by generating an "increase," which produces the next bloom stalk. The central rhizome of any iris can produce only one of these stalks and they usually take a year to mature and bloom. Rebloomers, however, have an accelerated growth cycle. Their increases mature and bloom within the same calendar year.
Gardeners in much of the country can enjoy reblooming irises. According to John Weiler, past president of the Reblooming Iris Society and an iris hybridizer and judge, up to 200 varieties of tall bearded, intermediate, and several dwarf bearded varieties will rebloom reliably in zones 5 through 10 (with the exception of Florida and the Gulf Coast where high humidity and rainfall put a damper on remontancy). A few varieties rebloom in zone 4, and one variety, 'Immortality', even reblooms in zone 3. And we can expect more within a few years.
Iris fanciers predict that within 20 to 25 years, irises will achieve the same reblooming reliability of roses in severe as well as mild climates. Joan Roberts is a hybridizer who grows more than 1,000 iris varieties at her Maryland property where she also operates a mail-order nursery, Friendship Gardens. She grows 375 bearded reblooming irises and reports that she harvests flower stalks as late as November.
Iris experts have not been excited about rebloomers until lately because their flower form and coloration were considered inferior to the one-time bloomers. But those same experts are changing their minds as hybridizers create rebloomers that are so good they're even starting to garner a few awards at flower shows.
I also enjoy them because they add an element of surprise. John Furman, a garden hobbyist, and hybridizer Tom Carruth nurture thousands of plants in their garden in Altadena, California. "You don't really notice they're going to bloom until the flowers are close to opening," says Furman.
Like icing on a cake, many rebloomers have another tantalizing delight -- they're fragrant. Some are redolent of an aroma resembling grape juice. Others have a sweet, honey scent. These rebloomers are wonderful in floral bouquets where they perfume an entire room.
Plant reblooming irises in summer so they can root before winter. They'll thrive in almost any location that receives at least five hours of sun and that has slightly acidic, well-drained soil. Set rhizomes 1 to 2 feet apart at ground level so that they are exposed to sunlight. Point the rhizome in the direction you want it to grow. Growth will continue from the leaf end. If you live where soil freezes, mulch new plantings in winter to prevent soil heaving. East of the Rocky Mountains (except for the Gulf Coast) iris borers are a common pest; during the growing season, keep the iris bed clean and unmulched to eliminate their breeding areas.
Remontant irises have accelerated life cycles. They grow and flower faster than the one-timers so they need additional fertilizer and water. Avoid high-nitrogen fertilizers that encourage vegetative growth. Use a balanced fertilizer, such as 10-10-10, in spring and again in summer (in warm climates feed four times yearly). Water deeply in August and September if rainfall is scarce. After four years, clumps will become crowded and need dividing and replanting. At planting time, lift the clump with garden forks. Remove the nonproductive rhizomes in the center, and carefully break apart the clump.
Save the large new fans with foliage. You'll have extra to share with friends.
The popularity of rebloomers has been limited by their scarcity. Nurseries and garden centers usually have few for sale. The best source is iris growers specializing in rebloomers. They will advise you which varieties perform best in your area.
In these lists, Zone 10 refers to arid regions only. Irises won't rebloom in hot, humid regions in zone 10 (Gulf Coast and Florida).
Karen Dardick is a garden writer based in Los Angeles.
Photography by Suzanne DeJohn/National Gardening Association
Article published on June 23, 2008.