Hybridizing irises: a world-renowned breeder of Japanese and Siberian irises shares the secrets of his success - Dr. Currier McEwen; includes sources

Flower & Garden Magazine, April-May, 1993 by Marian Gagnon

You Don't Have to To Be a celebrated iris hybridizer like Dr. Currier McEwen to create lovely, never-before-seen varieties of irises. It just takes some basic know-how -- and a good measure of luck. In fact, it was a fluke early in McEwen's hybridizing career that yielded the very first yellow Siberian iris.

To McEwen, who loves to retell the tale, it's the perfect example of the importance of luck in iris breeding. A friend from England sent him the seeds produced by two blue irises, |Dreaming Spires' and |Cambridge,' each pollinated by an unknown male parent. When the resulting seedlings bloomed, two-thirds of each group had blue flowers, and one-third were white. He was delighted to find that in each group of whites, there was a seedling with flowers that were slightly yellow in color.

When he crossed those two plants he obtained an iris with distinctive yellow falls (the three lower petals) and white standards (the three upright petals). He aptly named it |Butter and Sugar' and registered it through the American Iris Society, bringing him instant fame among iris hybridizers.

"It just goes to show you," McEwen says. "If I had set out to produce a yellow, I would never have started with two blues."

That was in 1968. McEwen has had a love affair with hybridizing Siberian and Japanese irises ever since. "Once you get bit by the hybridizing bug, it's a serious disease" he quips.

At age 91, McEwen still avidly gardens at his South Harpswell, Maine, home. Every summer thousands of McEwen's irises lap up the moist sea air and salute the sun's unobstructed rays as they sway in the breeze from the Merriconeag Sound. And every summer new hybrids are born.

These days, the former Dean of Medicine at New York University crosses about 400 Japanese and Siberian irises each year, introducing three to six new hybrids each spring. There was a time when he crossed several thousand each season.

McEwen can claim many "firsts," including the first tetraploid Siberian and Japanese cultivars to be introduced to home gardeners. (Tetraploids are plants with four sets of chromosomes instead of the usual two sets found in diploids; they are often stockier plants, with larger flowers in richer colors.) His accomplishments have brought McEwen recognition as an international authority on Japanese and Siberian irises. His book, The Japanese Iris, published in 1990 by the University Press of New England, is the first definitive treatise on Japanese irises in the English language. The same can be said of his book Siberian Irises, published several years ago by the Society for Siberian Irises.

To the average gardener, hybridizing irises may seem an awesome task. But it's really quite easy, says McEwen. Begin with a half-dozen or so of the best varieties you can find. Choose flowers with the characteristics that match your specific hybridizing goals. To increase chances of genetic compatibility, stay within the species or group, whether it be Siberian, Japanese, tall bearded or any other. Also, be sure you are crossing diploids with diploids and tetraploids with tetraploids. Before you attempt a cross, study the anatomy of the iris so you can easily recognize its reproductive parts.

In order to know both the female parent and the male parent, select two buds that are expanded and almost ready to open, but are still curled shut. That way you can ensure that a bee or insect hasn't already done the hybridizing for you.

Carefully open the iris bud that is to serve as the male parent by pulling down the falls and exposing the stamens. Using a pair of tweezers, gently remove the anther (the pollen-bearing filament) from the end of a stamen. If the anther has not yet split open to release its pollen, store it deep in the center of the iris and tie the flower closed with either a twist-tie or a thin strip torn from the plant's own foliage. This will protect the pollen from bees until it is ready for dusting, several hours later or the next day.

Likewise, open the iris that will be the female parent and snip off the three stamens. Rising upward from the base of the falls are three firm, petallike styles. The small liplike structure on the lower (outer) surface of each style is the stigma -- the female, pollen-receiving portion of the flower. Be sure that the stigmas are slightly curled away from the styles, indicating that the flower is sexually receptive. If the stigma is tight against the styles, tie the flower closed and wait a few hours, as the blossom is not yet ready for pollination.

When you're ready to make the cross, untie the flower and, using tweezers, brush the anther of the male parent against the underside of all three stigmas of the female parent, transferring pollen. Protect the flower from insects by lifting the falls over the styles and securing them with a twist-tie or a strip of iris foliage. Tag the flower with the names of the parent plants, and document the cross in a book. Since iris flowers contain both male and female parts, McEwen doubles his chance of success by making a reciprocal cross each time he hybridizes a pair of irises.