Fred W. Cassebeer, a well-known iris hybridizer, shares what to select for in your breeding and how to make the cross.
If the average gardener were suddenly asked, “What does a hybridizer do?”
He might think first of the development of the fuzzless peach or, perhaps, the plum tomato, but he would probably be at a loss to explain how hybridizing is done or just what role it plays in the gardening scene.
Little is known generally about the hybridizer or his work.
Perhaps this is because a relatively small number of people are actively engaged in this field, or possibly, after all, for the most part, results are achieved slowly and, therefore, do not receive dramatic publicity.
Work Of The Hybridizer
The work of the hybridizer—the development of new varieties of plants—is painstaking and time-consuming, for careful records of cross-pollination must be kept, and often many generations of the plants are grown before desirable results are achieved.
However, in recent years, an increasing number of amateur breeders have taken up hybridizing as a fascinating and rewarding hobby.
One flower that has attracted many professional and amateur hybridizers are the tall bearded iris.
This is probably due to the beauty of the flower itself, and, perhaps more important, to the comparatively “quick” results that are possible—the “new creation” may be observed and further work done with it only three.
Sometimes even two years after the original cross was made!
Most Horticultural Hybridizing
As in most horticultural hybridizing, the iris breeder aims to improve the flowers and the plant.
The blossoms can be bettered in color, form, substance, and size if the primary aim is the creation of bigger and better flowers.
As for the plant itself, there is always room for improvement in the branching and sturdiness of the stalk, the attractiveness of the foliage, or vigor and disease resistance.
Breeder’s Purpose In Color
In color, the breeder’s purpose is usually to improve the clarity of tone and the intensity of the hue and to eliminate any objectionable markings from the falls (lower petals) of the iris bloom.
He may also wish to obtain new and interesting variations from existing colors. An illustration of this is the comparatively new strain of coral, strawberry, flamingo, and orchid pinks that originated within the past decade by such breeders as David F. Hall. Dr. P. A. Loomis and others.
Other new colors are the beautiful golden brown blends being produced by Dr. R. E. Kleinsorge and Fred De Forest, as well as some New England hybridizers.
An iris blossom with good form has a firm, arched standards (the three upright petals) and flaring or semi-flaring falls (the three lower petals) that are broad and of good substance.
A ruffled and waved blossom is usually more desirable than one of plain, tailored form. It is a combination of an intriguing color and an attractive shape that gives an iris flower a certain charm and makes it desirable.
Also, the blossoms should be pleasingly spaced on a well-branched stalk of good proportions so that the iris plant will have a graceful appearance.
Task Of The Iris Breeder
The task of the iris breeder is to fulfill these ideals of color, form, and substance by whatever means are at his command.
For success, the amateur hybridizer should use as stock the best-bearded iris varieties, preferably those of recent introduction.
Also, he should decide right at the beginning what line of hybridizing he intends to pursue.
If he wishes to work for color improvement, then let him pick one or two colors to work with, such as yellows and purples, and purchase several outstanding varieties in these colors to use as parents in his breeding work.
Results are much more certain for the beginner if he does his crossing between iris of the same color or related shades.
Line Breeding
For example, if he crosses two yellows of different forms and characters, he is certain to get a large proportion of yellow seedlings, some of which may be more attractive than either of the parents.
These seedlings can then be crossed with each other or back on one of the parents to produce a second generation of yellow seedlings. These, in turn, are again crossed among each other.
This type of procedure, which is called line breeding, is practiced by many hybridizers, notably Paul Cook with his purples and Dr. Kleinsorge with his group of tan, bronze, copper, brown, and reddish blends.
In-line breeding varieties of other hybridizers are often used with one’s seedlings to introduce another variable factor that might improve the line.
When two iris that are dissimilar in color and character are bred, it is called a wide cross.
In this case, a breeder hopes to obtain a new break in color or form that can be improved upon after several generations of further breeding.
Unless this is done with considerable scientific knowledge, the results are usually disappointing, and the seedlings thus obtained are often a miserable-looking lot of so-called ‘‘dogs.”
Mating Of Two Dissimilar Parents
In rare instances, mating two dissimilar parents produce seedlings with hybrid vigor, which later become fine parents for further breeding.
Initially, the amateur is much safer to stick to crossing flowers that are closely related in color.
After the prospective iris parents are chosen, the crossing mechanics consists of transferring the pollen on the anther of one blossom to the stigmatic lip of the other.
This stigmatic lip is located just below the crests in the flower’s heart and looks like a protruding shelf. Immediately under the stigma is the stamen, with the anther containing the pollen.
Most breeders remove the entire stamen utilizing tweezers. Then holding the stamen with the tweezers, the pollen side of the anther is rubbed against the stigmatic lip of the second flower, thereby transferring some of the pollen.
Fertilization Effect
While it has been established that pollen placed on one of the three stigmas of an iris blossom is sufficient to effect fertilization, it is usually a good practice to rub the same pollen on each of the other two stigmas to make doubly sure that it will take effect.
All expert hybridizers have their favorite procedures for pollinating. I believe that the best time to do this is late morning on a dry, sunny day.
The pollen should be taken from a newly opened blossom as soon as it is powdery and brushed off easily from the anther.
Conversely, in my experience, the stigmatic lip of an older blossom more readily receives the pollen than the still tightly pressed lip of a newly opened blossom.
Self-Fertilization
As the chance of self-fertilization or cross-pollination by insects is very slight in the iris, the usual precaution of bagging a flower before and after pollinating is hardly necessary.
Some hybridizers do cut away all of the falls of the pollinated blossom to preclude any remote chance of fertilization by a pollen-bearing insect alighting on the falls.
After a cross has been made, the stem should be carefully tagged just below the pollinated blossom so that the cross is recorded.
Pollen Parent and Seed Parent
The labels should bear the name of the variety, that is the recipient or female (seed parent), followed by the name of the male (pollen parent).
If a cross is a successful “take.” the ovary just below the withered blossom will begin to swell and form a pod within four or five days.
These pods will continue to grow in size for several weeks and mature in about six to eight weeks when they look rather like a miniature watermelon. When the pods begin to turn brown and split open at the top, it is time to harvest the seeds.
These will be found in three compartments arranged like kernels of corn on a cob. A healthy pod will produce from 25 to 60 seeds.
Treating Newly Harvested Seeds
Where there is a considerable difference of opinion among the experts about how to treat the newly harvested seeds and just when to plant them, we have found that air-drying the seeds for several weeks and then planting irises in a cold frame late in October will produce entirely satisfactory germination in the spring.
If the seeds are planted soon after harvesting, some of them may germinate in the fall, and the young seedlings are apt to receive a severe setback during the winter.
The soil in the cold frame should be mixed with a little sand and plenty of humus, peat moss, vermiculite, or other water-retaining materials and carefully sifted to a depth of several inches.
The iris seeds are then sown in drills about an inch deep and 6” to 7” inches apart. The iris seed should be spaced in the drills, not closer than ½ inch apart.
Firm Soil After Sowing
After sowing, be sure that the soil is firmly tamped down, then water and leave the frame open without a sash for the winter.
However, a mulch of salt hay or excelsior after the frozen ground is strongly advised to prevent heaving.
Remove the mulch very early in the spring—the first week in March—and cover the frame with the glass sash.
From this point on, it is important to keep a close watch on the cold frame, ventilating it during warm days and covering it again with the sash on cold days and at night.
At the same time, the soil should be kept constantly moist, even if it means watering occasionally. As a result, the iris seeds usually begin to sprout during the last two weeks of April.
At this time, to ensure maximum germination, it is especially important not to let the soil dry out. Any germination results above 50% percent are considered good.
The manner and time of transplanting the young seedlings from the cold frame depend largely upon the space available in the hybridizer’s garden and the demands upon bis time.
Seedlings Should Be Transplanted
If possible, the seedlings should be transplanted in May while they are still tiny and set in a carefully prepared seedling bed enriched with natural fertilizers such as dried manure, bonemeal, or superphosphate, and humus in the form of pulverized Icafmold or peat moss.
These beds, which should be located in a sunny place with good drainage, should be about 5’ or 6’ feet wide for easy cultivation from either side.
In these beds, the baby seedlings are set out about 8” or 10” inches apart each way, and markers are carefully put in front of the seedlings from each cross to denote the number of seedlings planted and their parentage.
If these May-planted seedlings are kept watered during dry spells in the summer, they will give a high percentage of blooms, generally about 75% percent, the following spring.
If the press of spring work is such that it is not possible to set the seedlings out as early as May, one may wait until the early part of August when they are much larger and have well-developed root systems.
Transplanting In Midsummer
When transplanting in midsummer, it is best to set the seedlings in a larger space in rows about 3′ feet apart with plants spaced one foot apart.
While this late planting will seldom give more than a smattering of bloom the following spring, it has the advantage of resulting in close to 100% percent bloom the second year, when the plants will have formed clumps.
Although this late setting out of the seedlings usually will delay the first flowering for a year, it will give the hybridizer a much better basis for appraising his seedlings, for they will have full clumps rather than single stalks, and after all, the ultimate use of the iris in a garden will be as clumps.
When the hybridizer believes a seedling has merit, he will number the plant and record the number with a brief description of the flower and the cross from which it resulted.
Some weeks after flowering, he will divide a portion of the clump and set the divisions out for increase.
If, after growing the new seedling another year or so, he is fully satisfied that it has some exceptional merit, he will name it and register the name with the American Iris Society for a fee.
When through the careful subdivision, he has increased the number of rhizomes to 50 or more, he is ready to introduce the new variety either himself or through a dealer.
The iris breeder may aim to improve the clarity of tone and the intensity of the hue of the bloom or to obtain new and interesting variations from the existing colors.
The hybridizer may also strive to improve the shape and substance of the bloom, the sturdiness and branching of the stalk, or the spacing of the flowers.
8 Step By Step Operations In The Development Of A New Variety Of Iris
Here is the step-by-step guide to developing a new iris variety.
- Using a pair of tweezers, pinch off the stamen (anther) of the variety you will use as the mate or pollen parent.
- When the pod ripens and splits at the top, remove the seeds and store them with their tag in an open container.
- Roll back the crest of the female or seed parent, and brush the pollen-laden anther across the top of the stigmatic lip.
- After you complete the cross, pull off the three falls and tag the blossom, recording the parents of your cross.
- If your cross has been a successful “take,” the ovary will begin to swell and form a pod within 4 or 5 days.
- In late October, sow the seeds in the cold frame in drills about 3/4” of an inch deep and 6” or 7” inches apart.
- The seeds will germinate at the end of April. When the seedlings are 3” inches high, they may be transplanted.
- Plant the seedlings 8” to 10” inches apart in a sunny, well-drained bed, and label each variety carefully.
44659 by Fred W. Cassebeer