Garden 5(5): 16-19 (Sept/Oct 1981)
Iris With Two Lives
Some varieties yield exactly twice as much iris beauty—by blooming first in spring and then again in late summer or early fall
Dorothy Yoerg

... to produce fall flowers. After reblooming, another round of new increases grows out of the second set of rhizomes. These also mature sufficiently to rebloom the next spring. Thus rebloomers undergo two complete life cycles each blooming season.

The tendency to rebloom has been discovered in many iris species. The reblooming trait is inherited.

Rebloomers—rediscovered

The reblooming iris was first seen in Portugal in 1565. Records reveal that this variety of Iris subbiflora bore a flower undistinguished but for its appearance in autumn. In 1597 Gerard wrote of another iris, I. biflora, that "Twice Flowering Flower de-Luce … in Autumn (it) flowereth againe and bringeth foorth like flowers."

This kinde of Flower de-luce came first from Portingale [Portugal] to us. It bringeth foorth in the spring time flowers of a purple or violet colour, smelling like a violet, with a white hairie welt downe the middle. The roote is thick and short, stubborne or harde to breake. In leaves and shew it is like to the lesser Flower de-luce of Dalmatia, but the leaves be more spred abroad, and it commonly hath but one flower upon one stalke, which in Autumne flowreth again, and bringeth foorth the like flowers, for which cause it was called Iris biflora.

Rebloomers received little additional attention until late in the 19th century, when in England in 1893 a grower introduced a bearded rebloomer of intermediate height, 'Crimson King.' It was soon followed by two other purple varieties that also seemed to be repeat-bloomers, or remontants, in warmer climates.

As early hybridization efforts proceeded, there appeared in 1926 in France a dwarf bearded iris, a yellow bitone and a blue-violet, all blooming in spring and autumn. At about the same time two brothers in the U.S. Midwest, Hans and Jacob Sass, produced good cold-climate repeat bloomers of intermediate height. Outstanding contributors of plants of better form, substance, color and branching, they introduced the tall iris then in great demand as well as intermediate rebloomers.

Another pioneer hybridizer, Dr. G. Percy Brown, developed some outstanding winter-hardy rebloomers. His 'Autumn Twilight,' with gold standards (three petals going up) and lavender falls (three petals going down), developed many years ago, is still the most dependable rebloomer in my garden. Dr. Brown bred other rebloomers as well. Each new introduction was of better quality than its predecessors.

'Royal Summer' (left, with swallowtail) and 'Golden Encore' are among the many iris now available that rebloom in the fall. Increasing interest in rebloomers has encouraged breeders to develop many high quality reblooming varieties.

The elusive fertile offspring

Unfortunately, while many rebloomers were developed, acceptance was slow because not all the new varieties would reliably repeat bloom. To compound this difficulty, many reblooming-iris breeders were enthusiastic amateurs who had a great deal of experience with trail-and-error hybridizing but little knowledge of genes and chromosomes. Many of these early hybridizers tried to cross two diploids (plants each of whose cells contained two sets of chromosomes), unaware that the offspring were likely to be sterile. Many breeders in the 1930s and 1940s quit when sterility persisted.

Then breeders of once-blooming irises discovered that when diploids were crossed with the larger-flowered tetraploids (those with four sets of chromosomes), the offspring would have more brilliant color patterns, and better form, substance and branching.

Those working with rebloomers tried to capitalize on this discovery, but met with frequent disappointment. Then in 1936 Dr. Brown successfully crossed a reblooming diploid with a reblooming tetraploid. The result was the lovely deep-blue-lavender 'September Sparkler,' said to come close to being everbearing. 'September Sparkler' was eventually used to parent many vigorous, disease-resistant rebloomers of high quality.

Meanwhile, the once-blooming iris had been dramatically improving in color and form, while the rebloomers, although greatly improved, were by comparison muddy-colored and not as well formed—some had snaked flower stalks! Breeders continued to use the better seedlings, however, and over the years have developed dependable and truly beautiful remontants.

Choosing a rebloomer

A gardener selecting rebloomers should be careful to get those appropriate to the climate. Rebloomers must be able to bloom before a hard freeze descends. The iris originating in a warm climate but grown in colder ...

... soon as rhizomes arrive, probably in July or August, they should be disinfected to prevent plant diseases becoming established in the new iris bed. Soak rhizomes in a Clorox solution, one tablespoon per gallon of water, for about half an hour, then transfer the plants to clear water for another half hour. (This is important to prevent disfigurement of blooms.)

The iris roots may then be placed in a weak fertilizer solution for a short time, but they should not remain in water indefinitely. Plant them as soon as possible in a prepared hole. Spread out the roots gently and make certain that the rhizome is flush with the ground surface, with part of the rhizome exposed to the sun. Do not hill up, but firm the soil around the plant. Water well until new growth appears, then water when necessary.

To prevent the soil from drying out completely, a mulch or black plastic sheet may be used between plants, but the mulch should never cover the rhizome.

The soil for rebloomers should be very rich in organic matter and high in nutrients. Compost, sand, gypsum and vermiculite (the last three especially for soil with a clay base), bone meal for bearded varieties, and cottonseed meal if it can be found, are added to garden soil. High nitrogen will encourage growth but not bloom; for superior bloom, phosphate and potash are needed. The commercial formula many irisarians prefer is 5-10-10 or 1-4-4, well mixed in the soil before planting if possible.

Peat moss may be valuable, especially where the soil is sandy. There is a difference of opinion about manures. Some sterilized manure a foot below ground level is helpful, but it should never touch the rhizome since it contributes to rot.

Borer eggs are laid on iris leaves in small inconspicuous masses, so if all dead foliage from the preceding year has been removed and burned, the iris plant has a chance of avoiding borer damage. However, spraying or a soil drench may still be necessary, chiefly in April and May, in areas where borers abound. Spray every ten days for about six weeks with an all-purpose spray. The local garden supply store may recommend Cygon 2E, Isotox or Daconil.

The gardener must choose to spray or not, taking into consideration the risk to pets, birds and wildlife. Some sprays used according to manufacturers' instructions may disfigure the iris blooms. It is best to use less than the amount recommended on the label. Some growers vary the spray so insects are less likely to become resistant.

Chemicals mixed in the soil to prevent or kill weeds are not recommended near newly planted irises. At least one year's growth is necessary before a herbicide is used, and even then with caution. Chemicals have been known to cause deformed iris bloom or even plant death.

In The World of Irises Raymond Smith writes, "To obtain rebloom demands a singleness of purpose foreign to many gardeners," and indeed it is true that anyone who values iris rebloom will have to be willing to devote more time to these varieties. The reblooming iris fancier in cold climates accepts the challenge.

Connoisseur's guide to rebloomers

While the early rebloomers tended to trail behind the once-bloomers in quality, a select few of the older varieties, and many of the newer varieties, are of high quality and great beauty. Many catalogs do not list iris as rebloommers even though they may sell them. You must know what you are looking for.

The following rebloomers are outstanding in form and substance:

The following are exceptionally dependable in cold climates:

'Lemon Duet' and 'Lemon Reflection' are two promising new introductions.


Bulletin of the American Iris Society - Issues 232-239 - Page 79 (1979)
Rebloomers
Dorothy Yoerg: Ulster Park, NY:

I did notice a distinct increase in rebloom in 1978. I attribute it chiefly to 3 things – 1. improved soil, 2. dividing large clumps of remontants and 3. an electric light (100 watt) in a lawn lamp about five feet from my reblooming bed that is lit about five hours nightly, except when the bulb burns out. This is my first and only experience with evening light. I do believe it helped encourage rebloom, as Myra Pollock reported recently in the Fall issue of the Reblooming Iris Recorder. I never put anything from the iris and rose beds into my compost piles. The state inspector here warned me about that some years ago. I burn everything from those places, and try to haul away the remainder (debris). SWEET GRAPES has not rebloomed for me and I've had it since 1975. I get good rebloom on DA CAPO, CROSSTITCH, I DO and NOW AND LATER. My iris set a record in 1978. I had bloom until October 18 (hard frost), then again bloom in November until the twentieth. Iris that were cut bloomed indoors until December 5.

Reblooming Iris Bibliography