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Development Of Reblooming Irises

From the "The World of Irises" Chapter 7, by Raymond G. Smith © 1978 AIS

'Rosalie Figge'Rosalie Figge


by Raymond G. Smith
Causing nature to respond in unusual and dramatic ways is a project that has long appealed to the creative instinct of persons with green thumbs. When such a challenge is coupled with the promise of renewed spring, it becomes enticing indeed. Such is the appeal of the iris that reblooms, for it furnishes not one, but two riots of rainbow color for the visual titillation of the addicted irisarian. The pathway to rebloom, however, although initially appealing to many, has been traditionally paved with difficulties so numerous and intractable as to discourage all but a small band of dedicated travelers. But during the past quarter century, and more especially during the past decade, progress has been rapid. Numerous new sorts have appeared, capable of competing in charm and overall quality, not with the best, but certainly with the better of the magnificent new tall bearded and median creations. Along with improved availability have come widened interest and increased support, evidence of which can be seen from the establishment of fall shows sanctioned by the American Iris Society, first in 1965 in California and later in Ohio, Virginia, and New Jersey.

The advent of official shows brought official awards, and Queen of Show has been won by such varieties as 'Early Snowbird', 'Summer Green Shadows', 'Joseph's Mantle', 'Bright Eyes', 'Cayenne Capers', 'Winter Gold', 'Red Polish', 'Western Hills', 'Bonus', Scheherazade', 'Helen Keller', 'Ruth's Love', 'Chant', 'Fall Glory' and 'Fall Fulfillment'.

Sectional status was given to the Reblooming Iris Society in 1967, and a regularly issued publication, The Reblooming Iris Recorder (initially the Reblooming Iris Reporter) has been in existence since 1962. The rebloomer organization sponsors test gardens, a free slide library, and annual median and tall bearded re blooming iris symposiums.

The potential of the rebloomer iris as a fall flower has not escaped recognition beyond the borders of the United States. A group of irisarians in Britain are now hybridizing and exchanging plants and seeds; and the annual International Competition in Florence, Italy, provides for a rebloomer section.


A rebloomer may be defined as any iris that produces an extra period of full bloom each year. By full bloom is meant bloom of one or more increases from each rhizome that flowered during the immediately preceding regular period. This definition excludes those sorts whose stalks emerge serially over an extended season, as well as clones with only a fraction of the mature rhizomes blooming during one period and the remainder during the next, even though 'such sorts do provide color apart from regular seasons and are frequently mislabeled rebloomers.

This definition also denotes an accelerated growth process. The central rhizome of any iris can bloom but once; the increases of a spring blooming plant normally mature during the growing season, and reach the bloom stage only by the following spring. The 'rebloomer trait requires a doubling of this life cycle. Two sets of increases must mature and bloom each season. In cold climates the offsets produced during, the. period of active spring growth must continue to grow throughout the summer and produce bloom the same fall. Increases produced during the fall bloom period must likewise mature sufficiently to bloom the next spring.

The rebloomer plant must possess a fan and root system capable of carrying on the rapid photosynthesis required for the double flowering cycle; it must also be capable of surviving the normally lethal shock of major tissue damage and invasion of disease-producing organisms when the new, succulent bloomstalk is subjected to hard freezes. The essential difference between the cold- and the warm climate rebloomer is in resistance to freeze damage; both must grow rapidly and bloom whenever the rhizome has sufficiently matured. (Many warm-climate originations succumb with the first hard freeze when introduced to the rigors of the Midwest. Conversely, many Midwest varieties do poorly on the West Coast, presumably due to the absence of the needed winter dormancy period. As a general rule all irises grow and perform better in climates similar to those of their origin; this rule applies with a vengeance to rebloomer sorts.

It should be noted that the above definition of a rebloomer iris is general for all species and cultivars. Rebloom occurs among many of the eupogon species and in some apogons, but because of the focus of interest of many hybridizers, most of the available varieties are either tall bearded or median bearded; consequently much of this chapter is devoted to these sorts.


As a rule, whatever horticultural practices optimize the excellence of a fancier's other irises will be best for his rebloomers. Because of the accelerated life cycle, the rebloomer requires more of everything-food, water, sunshine and cultivation. Any factor that retards metabolism, either absence or excess of any cultural need, can prevent or delay rebloom. Each variety must be provided with the optimal amount of everything it needs, neither too much nor too little. Many sorts require biennial resetting into new or rejuvenated soil. Some varieties will not rebloom the first year following transplanting. In order to assure that the grower will have some rebloom on such varieties it is necessary for him to grow two clumps and transplant them on alternate years.

Because of their greater requirements for nutrients and their expanded root systems, rebloomers should be spaced more generously than non-rebloomers. A fertilizer with 1-4-4 ratio of nitrogen, phosphates and potash is recommended. Whether commercial mix or home-developed compost is used, the plants should be fed all that they can absorb without developing rot or going dormant. An ideal growth medium, when available, is a liberal dressing of equal parts of sewage sludge and sand.

Some growers maintain that rebloomers should never be watered when the temperature exceeds 32 degrees C (90 degrees F) and others hold that it is wise to include a germicidal agent when temperatures are high. Substitutes for watering include dust mulch, sawdust, shavings, nut hulls, weed-free straw, marsh hay, or black plastic. These solve the moisture problem and control weeds.

Some growers have found that commerical weed killers or inhibitors of any kind, especially those that are not biodegradable and consequently build up in the soil, will discourage rebloom. For the control of insect pests by legal insecticides see chap. 23. 1


The rebloomer iris apparently appears adventitiously; it has been noted at least as early as the 16th century (figure 1) as reported by Dykes in The Genus Iris (1913). No effort was made by man to improve upon nature for nearly four centuries. Several excellent descriptions of the early varieties are readily available and these need not be repeated here. Likewise, the attempts of early hybridizers to create new rebloomers have been fully chronicled (Rundlett 1958, 1959) and will be omitted here.

The first rebloomers that achieved wide commercial distribution were sterile interspecies hybrids, 44-chromosome products of crosses between reblooming dwarfs of the chamaeiris complex and tall bearded sorts. These were products of a hybridizing program conducted by Hans and Jacob Sass in Nebraska during the 1920s and 1930s (Sass 1959). The wide cross gave hardy, disease resistant, floriferous, and attractive garden specimens that are still popular. The best of these reblooming Sass intermediates came primarily 'from crosses between the rebloomers 'Crimson King', from Barr in 1893, and the Sass 'Autumn King' of 1924, possessed of 44 and 46 somatic chromosomes respectively, and the 40-chromosome French dwarf chamaeirises Lt. De Chavagnac', and 'Jean Siret', both from Andre, 1926. During these early years hybridizers knew that a sterility problem confronted them but lacked our current knowledge of chromosomes that explains why crossing two hybrid intermediates fails to produce viable seeds. As a consequence of repeated breeding failures, most hybridizers gave up in their attempts to work with the Sass intermediates.

'Crimson King' 1893Crimson King 'Autumn King' 1924Autumn King 'Lieutenant De Chavagnac' 1926Lieutenant De Chavagnac

In the mid 1930s, however, G. Percy Brown (1956) of Barre, Massachusetts, succeeded in crossing a reblooming diploid of his own origination with the tetraploid 'Autumn King' and obtained one fertile, hardy offspring. When this seedling was backcrossed to 'Autumn Elf', it gave another tetraploid seedling which, crossed to Grace Sturtevant's 'Ambrosia', produced 'September Sparkler', the iris that became the progenitor of Brown's long line of cold-climate repeaters. Brown's rebloomers are characterized by vigor, dependability, disease resistance, floriferousness, and compound branching. Unfortunately, they are frequently marked by dirty hafts, poor substance, snaky stalks, narrow parts, and muddy colors. Brown's introductions total 78 and remain today the most dependable rebloomers available for severe climates.

In 1950, Raymond Smith of Bloomington, Indiana, began an independent program of screening the intermediates in search of fertile parents for developing rebloomers. The variety 'Southland' proved the most promising. It ultimately yielded a line of highly fertile offspring which unfortunately were characterized by poor hafts and poor substance and were discarded. Of several hundred older sorts tested, five proved to be fertile tetraploids. These included a famous old white named 'Polar King'; 'Autumn Flame', a Sass purple red, and 'Pink Lace', also from Sass; a blue-lavender, 'Martie Everest'; and the famous purple-on-white plicata, 'Gibson Girl'. Later the Hall variety, 'Happy Birthday', along with several of Hall's unnamed seedlings were brought into the program. These sorts were intercrossed with the objective of developing a variety of colors with better quality (figure 2). By the middle 1970s Smith had registered 30 rebloomers.

Also in the early 1950s Lloyd Zurbrigg of Listowel, Canada, working with 'Gibson Girl', F. Brown's 'Western Hills', 'Martie Everest', 'Autumn Flame', and an unnamed seedling of Tell Muhlestein's, was trying unsuccessfully to produce rebloomers that would perform in his frigid climate. When he moved to the United States in 1958 he made the pleasant discovery that these early efforts had in fact achieved a measure of success (figure 2). Zurbrigg, now of Radford, Virginia, subsequently registered more than 30 rebloomers and as of this writing is still hybridizing for improvements.


'Immortality' 1983Film  

Thirty-four warm-climate rebloomers of high quality were developed and popularized by Lloyd Austin of Placerville, California. Another west-coast hybridizer of high quality remontants was Thomas Craig of Escondido, California, and later of Hubbard, Oregon. At the time of his death he had registered 28 outstanding warm-climate varieties.

Craig's Rebloomers

'Persian Pattern' 1963Persian Pattern

The developer of the famous forebear, 'Gibson Girl', as well as of some of the world's finest modem plicatas, is James Gibson of Porterville, California. His 'Gibson Girl' resulted from a cross between the French Dykes Medalist, 'Mme Louis Aureau', and the hardy old Sass plicata, 'Tiffany'.


Various sources including personal correspondence and a review of the literature have suggested that the reblooming trait is widespread throughout the genus Iris. Simply because a particular clone of a species occasionally or even regularly reblooms does not make the species a rebloomer, however. A mountainside might be covered with a certain species, only one clone of which inherited a genetic constitution resulting in rebloom.

Rebloom has been noted in the following species: I. versicolor; I. olbiensis (I-44D and I-44F from 'San Angelo', 'Olbiensis Sannicandro'); I. subbiflora; I. albertii (from Rodionenko), I. mellita ; I. violacea; I. balkana (Darby); I. aphylla, I. biflora, I. nudicaulis, I. bohemica; I. uniflora; I. cristata; I. laevigata (alba); I. tenax; I. pseudacorus; I. pallida; I. ensata; I. pumila; I. ruthenica; I. graminea; I. bulleyana; I. variegata (remontant, Paul Cook); I. tenuis; I. innominata; I. setosa; I. unguicularis; and lacustris; in addition the natural hybrid forms of I. germanica, I. kochii and I. nepalensis; and the horticultural hybrid chamaeirises, Lt. De Chavagnac', 'Jean Siret'. Even allowing for confusions of identification and error in records, it is clear that rebloom has occurred in many species.

Several of C. G. White's arilbreds such as 'Black Joppa', 'Kalifa Hirfa', and the oncogelias 'Clara', 'Lutetia', and 'Dardanus' will rebloom. The 45-chromosome 'Lady Mohr' possesses the tendency as do Zurbrigg's arilbred intermediates 'Dead Sea Scrolls' and 'Once Mohr'. The genetic complex requisite for rebloom obviously has been passed down to certain individuals of the horticultural series, for rebloom occurs frequently in the miniature dwarf bearded, the miniature tall bearded ( 'Two For Tea'), and the standard dwarf bearded ( 'Twice Blessed'), as well as in the previously discussed talls and intermediates. It occurs in the Louisianas ( 'Pegaletta'), Japanese ( 'Scheherazade'), Siberians ( 'My Love', 'Violet Repeat'), Spurias ( Premier, I. halophila x 'Blue Acres') and 'Orchid Sprite').

First generation reblooming seedlings from interspecies crosses and between species and rebloomers have been reported: I. croatica (Straznjek); I. albertii x I. olbiensis I-44F; 'Gibson Girl' x 'Aphylla Wine-Red'; 'Bluet' x 'Illyrica Trieste'; I. douglasiana x I. innominata ; 'Gibson Girl' x I. croatica (Klanjec); I. albertii x I. balkana ; and 'Clear Sailing' x I. pumila (Schacht).

Geographically, varieties have been reported as reblooming in England, France, Germany, Switzerland, Canada, Australia (New South Wales), and Japan. There are members of the Reblooming Iris Society in 36 states, and in Canada, Japan and Britain. Although widely distributed, the trait appears infrequently within any individual species. Among the registered sorts, only about 500 are officially listed as rebloomers in all of the American Iris Society Check Lists published since 1939. The reblooming trait, however, is firmly established in the lines of current hybridizers, with many reporting rebloom from 50 to 80 percent of progeny from crosses of two reblooming parents.


Persons interested in growing rebloomers should be apprised of the existence of a number of special problems. Anyone living in the northern tier of states, that is, in or north of USDA hardiness zone 4 (US Department of Agriculture Miscellaneous Publication #814) will find it virtually impossible to obtain rebloom with present varieties, and an attempt to do so is generally a waste of time and money. Even so, it might be noted that the Dunbar miniature dwarf bearded 'Velvet Toy' has been reported as a reliable rebloomer in Stillwater, Minnesota, for several seasons.

One may expect success in hardiness Zone 5 about half of the time or less, and will experience occasional failures in Zone 6. Fortunately even when an early freeze takes the open flowers, later stalks will again produce, provided a warm spell lasting a couple of weeks or more follows.

Any fancier who purchases varieties from areas with climates or soils quite different from his own cah anticipate problems until the plants are fully acclimated.

Persons new to growing rebloomers can expect to devote more care and attention to them than they do to standard sorts. Not only is the period of care extended over the full summer season, but the time schedule generally is telescoped. All cultural activity is accelerated. Grooming and cultivation must begin earlier in spring; transplanting must take place as soon as the last flower fades; plants cannot be permitted the luxury of dormancy as a consequence of inadequate care or shipment delays. Sandy soil always requires extra moisture and fertilizer and with rebloomers even more is needed.

When transplanting some growers remove the soil to a depth of 45 cm (18 inches) and incorporate a mixture of earth, fertilizer and compost 30 cm (12 inches) or more below the roots of the transplanted rhizome. This supplies the necessary sustenance for at least two years. In areas with early frosts, caps or plastic shields must be provided. Furthermore, the grower should be prepared to cope with insect pests ordinarily presenting no problem in the spring. Spraying for such pests may eliminate them but also wilt or disfigure the irises. Special problems arise in each geographical locale and no universally successful rules can be prescribed.

The double life cycle that produces two new plants and flower stalks where ordinarily one would grow results in diminished flower quality. This problem has plagued growers from the time of the early Sass varieties and remains unsolved. The constraint of accelerated plant growth makes it difficult for a hybridizer to produce reblooming seedlings in sufficient number to provide a wide choice of forms and colors. The aspiring gardener must therefore accept whatever is available for his particular climate. The most serious problem confronting the new grower, however, is that expectation exceeds possibility. When the iris lover reads a glowing description of a visit to an autumn garden in full bloom, he little realizes the amount of struggle and effort that have entered into its actualization. He may rush out to acquire rebloomer rhizomes only to suffer disappointment and disillusionment. The reality is that rebloom does not peak as does bloom in the spring. Fall bloom begins sporadically in late July and gradually accelerates over a four-month time span. Consequently, the grower finds the diluted visual picture disappointing. In addition, fall flowers generally lack the perfection of those of spring. The absence of spring rains along with shorter days means less well-nurtured plants and less intense colors. Oddly enough, instead of from five to seven well-substanced flowers, the stalk of the vigorous fall blooming plant generally sports from seven to fourteen. The result of this increased florescence is a reduction in flower size and substance.

Many of the special cultural problems have previously been noted. The rebloom gardener must be prepared to ward off mid and late-summer invasions of disease or insects. There is little time for relaxation or attention to other floral delights. To obtain rebloom demands a singleness of purpose foreign to many gardeners. Disappointments abound. The plants selected must thrive in the particular climate provided. Major differences exist among available cultivars. Varieties originating in one climate may fail to perform in another. However, the returning beauty of spring, manifesting itself amidst the golds and browns of the autumn season, is within the reach of the avid gardener. By scaling down his aspirations to a size consonant with reason, by recognizing the special needs and problems that accompany successful culture, by devoting extra care to these special charges, the new grower of rebloomers should realize at least a modicum of success. Here is a challenging outlet for a creative spirit and a green thumb.

[Editors note, the above was written prior to 1978. much progress has been made. One can learn more by joining the Relooming Iris Section of the American Iris Society. ]

Continued from Chapter 6 Border Bearded Irises

For more information on historic Irises visit the Historic Iris Preservation Society at

-- BobPries - 2015-12-01
Topic revision: r12 - 05 Sep 2017, BobPries
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