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The Quest for Reblooming Louisiana Irises BY CLARENCE MAHAN
Louisiana irises are hybrids of iris species in Series Hexagonae. The most commonly recognized species in this series are native to the wetlands of the semi-tropical regions of the Gulf States. The exception is Iris hexagona whose home ground extends along the Atlantic coast from Florida to the Carolinas. Iris brevicaulis and Iris fulva have extended their natural habitat up the Mississippi River, with occasional clones found in areas along the Ohio River. Iris fulva has even been reported growing in the wild far north as Ontario, Canada.
Origin of
Modern Hybrids One of the most significant events in Louisiana iris breeding was the introduction of tetraploid cultivars by Joseph Mertzweiller. Mertzweiller doubled the chromosomes of diploid cultivars with colchicine. His first tetraploid cultivars, PROFESSOR IKE and PROFESSOR CLAUDE, were introduced in 1975. He subsequently introduced a number of additional tetraploid Louisianas. If one wanted to hybridize Louisiana irises with the objective of achieving reliably remontant cultivars, how would one go about it? There are several facts that should be considered in searching for an answer to this question. First, most, if not all, dependable cold climate reblooming bearded irises are hybrids. Second, all reblooming bearded irises seem to be either sterile or tetraploid cultivars. Another important fact to keep in mind is that the capability to rebloom requires an iris with great vigor and a favorable climate. Even a superlative remontant bearded iris such as IMMORTALITY will not produce fall bloom with abandon in the Syracuse, New York, area. The growing season is simply too short to facilitate frequent rebloom. How does one obtain hybrid vigor? The answer to this question is, of course, that one obtains hybrid vigor by introducing new species into one’s hybridizing program. There is a gene pool available that is virtually untapped in the development of Louisiana irises. This gene pool is to be found in Florida. The best article on this subject is Philip Ogilvy’s “Louisiana Iris: A Literature Review” in Gardening with Iris Species (St. Louis, 1995).*
Florida Potential Bringing new species into one’s iris breeding program would be worth doing even if remontancy were not obtained. Great breakthroughs in form and color have been produced in bearded irises by just such means. The possibilities of such results are apparent when one examines the beautiful and unique flower of Iris albispiritus shown in Plate 450 of Addisonia, Volume 14, Number I (March, 1929). Some clones of Iris hexagona have a vibrant, pure blue color which I believe is unrivaled by the color of any species except Iris laevigata. Breeding new Louisiana irises using this species might produce very exciting results. Remembering that dependably remontant bearded irises did not appear on the scene until tetraploidy was established, the iris breeder seeking be clever and consider using colchicine to elevate the chromosome level of Iris hexagona and the other Florida natives. This is not an easy task. One must expect many losses before viable tetraploids are obtained. Chances of success with this technique could be improved by consulting with iris breeders who have successfully used this technique with other types of irises. Currier McEwen and John White are two hybridizers who are very knowledgeable about the use of colchicine, and in my experience they are both quite willing to share their experiences. Which of the modem Louisiana irises might prove to be the best candidates to cross with the Florida irises to obtain rebloom? RED ECHO is a logical candidate because it has demonstrated a remontant tendency. Knowing that some Louisiana irises are not cold hardy, one might be wise to choose cultivars from lines with strong backgrounds of Iris fulva or Iris brevicaulis. Colchicine could be used to bring these irises to tetraploid level. The Mertzweiller tetraploid cultivars might also be good candidates to use for remontant breeding.
Clarence Mahan is a past president of the American Iris Society. This article is reprinted from The Reblooming Iris Recorder, Spring 1999. (And the Fall '99 issue of the SLI Newsletter). Worldiris.com Louisiana Rebloomer Introductions
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Henry Rowlan introduced the
Louisiana iris RED
ECHO in 1984. I immediately
ordered it. I had learned that this
iris, which resulted from a cross of
TARNISHED BRASS and a clone of
Iris fulva, would sometimes rebloom.
RED ECHO grew in my northern
Virginia garden for several years
producing lovely red flowers in the spring
but no rebloom. I had almost given up on
it when the late Rich Randall of Virginia
Beach brought a stalk of RED ECHO to
our local Fall iris show. The very next
year RED ECHO rebloomed for me in
October.
There are occasional reports of fall
bloom on several Louisiana iris cultivars.
BLUE DUKE (Arny 1963) and FOR
DAD (Pryor 1996) are two that come to
mind. The fall performance of these
Louisiana irises does not begin to
approach the level of dependability of the
best of our modern tall bearded irises, nor
does the performance of RED ECHO,
which is the cultivar most prone to
remontancy in the mid-Atlantic area.
I recently learned that Harry
Wolford, who lives on the East Coast of
central Florida has been having
considerable rebloom on his Louisiana
irises. This is not as surprising as it
might seem when one considers that his
growing season is virtually year round.
This reminds me of Gigi Hall telling me
that many Japanese irises rebloom in
her garden in Fremont, California.
When reliably remontant roses first
came to Europe and the United States, they were derived from crosses
between tender Chinese rose species and rose species native to Europe.
Almost all of the first generation of reblooming rose cultivars were very tender and rebloomed only in areas of mild climates. Indeed, most survived only in mild climates. This may also prove to be the history of remontant Louisiana irises. The day may come,
however, when reliably remontant Louisiana irises will, like modern roses, rebloom almost everywhere. It will take
some adventurous and persistent hybrid-izers
to achieve this goal.