Notes To The New Hybridizer
My Experiences In Developing the Robin Hill Azaleas
by Robert D. Gartrell, Wyckoff, New Jersey
Plant breeding is a fascinating hobby that everyone may enjoy. Hybridizing can be continued on a limited scale through the later years of retirement, for it can be as complex or as simple an avocation as you wish to make it.
Evergreen azaleas are a good choice for the amateur breeder since these plants require little space in the garden but produce buds within a few years; thus, less time and patience are needed than hybridizing with large leaved rhododendrons.
The excitement of watching your own creation come into first bloom is worth all the effort. You eagerly hope for that "special" hybrid having some outstanding quality not found in present day plants - something really new. Although it is difficult not to be sentimental about your own progeny, you must set high standards for your final choices. Seedlings not up to those standards must be discarded and this is not always easy to do. Having worked with evergreen azaleas for 35 years, some of my observations and practices may be controversial, but I would like to present my thoughts to the Azalea Study Groups for discussion and consideration.
I have a 3 x 20 foot cold frame and a small greenhouse (10 x 20 feet) which can accommodate some 1000 to 1500 seedlings and/or cuttings. I have set up nursery beds in my garden for my two year seedlings and cuttings. I find that I can simplify things as I experiment and learn more. For example, I believe that I could dispense with the greenhouse with only the loss of one year's growth. Joe Gable worked with the simplest of equipment and certainly had outstanding success.
I started my hobby with only one outside nursery bed - no greenhouse or cold frame. I began with delphiniums since I greatly admired these beautiful plants as grown in the perennial border and I am partial to blue flowers. Further, this work was done in Canada where delphiniums grow well. My goal was to increase the size of the bloom and the length and shape of the flower spike. My plan was that these would be grown as biennials; a cross would be made in one year and the results would be seen the following year.
I had no idea how to select plants to serve as parents but I had read enough of genetics and cytology to know that selection of parents was the most important step in any breeding program. I decided to self pollinate - that is a single plant would be both the seed and the pollen parent. I thought this would bring out both good and poor qualities fairly quickly. About 100 of my best plants were 'selfed'. The plant producing the largest percent of offspring showing the desired characteristics would offer the best chance that these characteristics, when crossed with another plant, would be carried through to the next generation. To some degree I verified this. One mediocre plant (No. 76) produced the best seedlings when crossed with other plants. This occurred regularly in many experiments. I had quite a few successes and won some prizes at local flower shows.
On returning to the States, I settled in northern New Jersey and continued with my hobby. I soon learned that delphiniums did not adapt to the new environment. They were beautiful the second year from seed but after that they began to deteriorate, and by the third or fourth year they were lost. I might have attempted to develop a strain suitable to the new location, but this was not attempted since I never learned how to propagate the superior cultivars I had created. There were no named delphiniums at that time.
Still intrigued with plant breeding, I sought more suitable material. I considered the daylily, the Primula, and even the violet, and finally settled on the rhododendron family. The large leaf rhododendron was ruled out as it required more room than was available. Also, most of these plants in my area were inclined to be leggy and in the 1930s they were considered very difficult to propagate. Having learned my lesson in this respect, I decided to look further. I finally decided on the azalea.
Here was a wealth of material to work with. They were evergreen and deciduous, varied in plant habit, leaf form, and flower, long lived, and successfully grown in wide areas of the country. Since evergreen azaleas were easy to propagate, I chose them exclusively for my breeding program. I decided that I needed to learn something first about the azaleas that were readily available and about the culture of these plants, so I purchased all the cultivars I could find. The Tingle Nursery listed 72 azaleas of all types in 1938. Most were purchased as rooted cuttings and other azaleas were added to my collection as they became available. After growing and observing them for five or six years, I felt I was ready to start hybridizing. Even at this time I realized the selection of parents was the all important step, since once the parents were selected and crossed all characteristics of the offspring were fully determined, apart from minor variations due to environment.
In the beginning, I did the obvious. I attempted to combine the good bloom and growth habits of one plant with the good foliage of another plant. One of the first crosses was an attempt to mate 'Gumpo' (large, frilled white flowers with low, dense plant habit with 'Glacier' exceptional foliage, lustrous dark green leaves). Thirty-two seedlings were grown on. Fourteen were discarded early, some for lack of cold hardiness and 18 were grown on to maturity. None had the growth habit of 'Gumpo' or the foliage of 'Glacier', so they were all finally discarded.
Continuing along this line- I grew several thousand seedlings to find promising Parents. Some 1800 were grown on to maturity. I judged that about 90 percent were fully equal to those sold under name by nurserymen, but they were not sufficiently different or better to be named and added to the already too long list of available azaleas. The entire lot was discarded.
I was not deterred by this since the whole venture was by nature a hobby/ experiment. As new cultivars became available, there was new material to work with and I felt there was room for improvement in evergreen azaleas. Many of the most beautiful, such as the tender Ghents (Belgians) and the Satsuki were not hardy and could not be grown successfully in the north.
From previous work, I was able to isolate one plant 'Oakland' which appeared to add hardiness when crossed with tender cultivars without changing the characteristics of the tender plant in the majority of cases. I had withstood very low prolonged temperature without damage. Another cultivar that showed promise was Gable's 'Louise Gable'. It not only added hardiness but the bloom often showed some degree of doubling, hose-in-hose, petaloidy, or both. It was later found that one of my own hybrids from a cross of 'Louise Gable' x 'Lama Giku' was an even better parent with similar properties.
About this time, Ben Morrison published a monograph on the Glenn Dale hybrids, giving not only a description but the parentage of each. He selected and named almost 500 cultivars. He must have considered that these were of sufficient merit to be introduced. There was concrete information for the would be hybridizer to study, but the plants were listed alphabetically by name. To put this information into a more useful form, I re-listed them by parents. It soon became apparent that some parents were better than others. I assumed that approximately the same number of seedlings were grown from each cross.
For example, from one cross he made, R. indicum x 'Hazel Dawson', he selected and named 24. From another cross, 'Malvatica' x 'Yozakura', only six were named. This latter group contained one of his best cultivars - 'Glacier' - with its remarkable foliage. None of the sister seedlings even remotely approached 'Glacier' in this respect. I repeated this cross on two separate occasions but no 'Glacier' foliage appeared. However, I found later that when 'Glacier' was used as one parent, the foliage of the offspring was improved in many seedlings.
Here is the story of 'Nancy of Robinhill'. The cross was made with 'Vervaeneana' (a tender Ghent hybrid much used as a 'florist' azalea) as the seed parent and 'Lady Louise' ('Louise Gable' x 'Tams Giku') as the pollen parent. All seed came from a single capsule. Twenty seedlings were grown on. 'Nancy' appeared as a surprise - none of the other seedlings of this cross had any similarity to 'Nancy'. 'Nancy' had the virtue of being equal to the tender Ghent in appearance, but most important, it was hardy to least -10 degrees - the genes for hardiness coming from 'Lady Louise'.
All breeding work is a gamble, particularly when working with hybrids of unknown parentage. This however, adds much to the interest as you may find yourself the winner of a sweepstakes!
If 'Oakland' (believed to be a kaempferi seedling) and 'Lady Louise' could add hardiness to tender azaleas without losing the good qualities of a tender parent, this should be the direction of my breeding program. For some time, a number of evergreen azaleas listed as Chugai hybrids (later known as Satsukis) had been available. I used some of these with moderate success - "Gumpo', 'Mai Hime', and 'Tams Giku'.
Some time in the 1950s, Dr. John Creech of the Department of Agriculture brought back from Japan a number of very desirable Satsuki hybrids, much superior to the older Chugai. These plants had very large flowers, as large or larger than the southern azalea, 'Formosa'. The flowers were what I call "flat faced" in form and had excellent evergreen foliage. They were low to medium in height and generally dense in growth habit. Unfortunately, they were not reliably hardy in the northeast. Among these were 'Heiwa', Getsu Toku', and 'Ama Gasa'. The flowers tended to vary slightly from season to season and some had brightly colored splashes on a white or pastel background. While this suggested they might be somewhat genetically unstable, I believed these hybrids might produce a generation with new shapes to the bloom, a variability of color, good growth habit, and possibly other surprises. But, these had to be combined qualities with hardiness, and the only way to do this was to make crosses. These Satsukis became a major part of my breeding program. (Details on some of these crosses follow later.)
Having considered the selection of parents, the next thing was to make the crosses. This is quite simple and I suggest that the new hybridizer learn something about the anatomy of the flower. I recommend an article by David Leach in the January 1975 Bulletin which has a helpful flower diagram. Making the cross consists of merely transferring the pollen from the anthers of one flower to the stigma of the pistil of the other flower. When the stigma is receptive and ripe for crossing, it will become glossy and sticky. The pollen is ready when the anther tips become white and sticky. When the pollen reaches the stigma and adheres, the cross is complete. The pollen tube will grow down the style until it reaches the ovary, where the egg will be fertilized. During the summer and fall, the ovary will swell to the size of a small pea.
I do not cover the flower after pollenizing to prevent stray pollen from entering, since I have found that the flower will not normally set seed unless crossed by hand. While the literature describes the pollen as grains, I find it is a sticky substance and I do not believe it can be wind blown readily. Normally, I only make the cross on one flower since I find each hand pollenized flower will set seed.
To keep accurate records, a small red tag is attached to the flower stem of the seed parent. Since the pollen plant is recorded on the tag, both parents are known. In my record book, I write the name of the seed parent first, followed by the pollen parent. Thus 'Nancy of Robinhill' is written 'Vervaeneana' x 'Lady Louise'. I have no evidence that it makes any difference which plant is selected to be the seed parent.
By Thanksgiving Day or a bit earlier, the seed pod will begin to turn brown and is then ready to be harvested. If left too long, it will burst and the seed will be scattered. After picking, store the pod in a warm, dry place. When dry and brittle, roll the pod between the thumb and fingers. Several hundred tiny seeds will be released.
No two seeds from the same seed pod will produce exactly the same character of plant. Working with hybrids, each seed contains a different and unknown combination of genes, so that many surprises can come from a single cross.
Having a greenhouse, I sow my seeds as soon as they are separated. I have had little success with year old seed. For germination, I use only milled sphagnum moss. Since this is difficult to dampen, I wet the moss before putting it in the container by squeezing as with a sponge. In this way you can be sure the moss is thoroughly moistened, but never soggy, since oxygen at the root zone is very important. For planting the seed I use an ordinary salt shaker in which I have placed the seed along with a small amount of sand to help distribution, I also add a very small pinch of seed disinfectant - Spergon - since I have never had damping off with this.
I tend to sow my seed too heavily in case germination is poor. However, it is better to scatter your seed sparsely since it will assist you in picking out the seedlings without disturbing the root system. After sowing, the surface of the flat should be moistened carefully with a fine mist to settle the seed in the moss. I do not cover the seed.
When the seedlings are large enough to handle, they are transplanted into flats containing a modified Cornell Mix, prepared as follows:
|Peat Moss||5 gallons|
|Coarse Perlite||5 gallons|
|5-10-5 fertilizer||6 tablespoons|
|Epsom Salts||1 teaspoon|
All ingredients are readily available. The resulting mix is porous but retains sufficient moisture to take the proper drainage it can hardly be over watered. It is sterile, weed free, and clean to handle.
"I have also germinated seed by using a shaded cold frame. In this case the seed is not sown until winter has set in. Milled sphagnum moss is used in a small flat completely enclosed in a -plastic bag. No watering is needed during the winter and germination starts in early spring. When the seedlings are large enough to handle, transplant them in flats containing modified Cornell Mix for the summer."
In the fall I move transplants to greenhouse benches for the winter months. The thermometer is set at 40 to 45 degrees F. It is usually said that 60 degrees is preferred but I find that azaleas make good growth at the lower temperature, with added advantages: reduced watering frequency and insects and diseases are discouraged. One spraying of Malathion and Kelthane in November is done as a precaution. In December, the plants are fed very sparingly with Osmocote, 14-1414, a slow release fertilizer.
The following spring, the small azaleas are put into outside nursery beds where they will grow until they reach blooming size (four to five years). These beds are carefully prepared by adding plenty of humus in the form of peat, leaf mold, or fine pine bark. After the ground is leveled, I rake in the following (for each 100 square feet): 12 lbs 5-10-5 fertilizer, 100 lbs gypsum, and 10 lbs superphoshate. In addition, I sprinkle on a water solution containing ¼ lb. Epsom salts and 3 tablespoons Sequestrene.
The plants are lined out in rows about 18 inches apart. To keep accurate records of the history and performance of each seedling, a number is assigned which will follow each independent seedling no matter where it is moved. This number remains as long as the plant is in my possession.
A simple system has evolved. When planting, each bed is given a letter of the alphabet, T, U, V, etc. Each row is given a number and the position of the plant in the row is given a number. Thus U14-5 identifies only one seedling. (This eventually was named 'Mrs. Emil Hager'.) To conveniently keep records, a notebook is assigned to each bed - a page to each row - and the position in the row is recorded on that page. Using this simple system, given the code number, I can easily check my record book to supply parentage together with comments about that particular plant as it grows. I have kept such records on several thousand seedlings planted since 1955.
The first bloom usually appears after four to five years from seed. Selection begins based on the first bloom - does it appear promising? Of course, the plant is too young to judge growth habit, foliage, or time of bloom. Final selection is not made until the plant has matured (in eight to ten years).
Here is what can be expected from a relatively good cross:
|PARENTS: 'Oakland' x 'Heiwa'|
|Number of plants set in open beds||33|
|Number of plants selected for growing||12|
|Number of plants good enough to assign tentative names||6|
|Number of plants registered at this time||0|
|PARENTS: 'Lady Louise' x 'Shinnyo No Tsuki'|
|Number of plants set in open beds||42|
|Number of plants selected for growing||8|
|Number of plants given tentative names||4|
|Number of plants registered at this time||2|
|Here are my notes on the two plants of this cross that were registered:|
|U14-5 'Mrs. Emil Hager'|
|Parents:||'Lady Louise' x 'Shinnyo No Tsuki'|
|Habit:||Very dense, low, 12", 10 years old|
|Flower:||3¼" H in H, Petaloides, Wavy, Appears Double|
|Color:||Roseine Purple, 68A, RHS Color Chart|
|Date of Bloom:||6/1/72, 6/1/73, 6/6/74 5/24/77|
|U17-8 'Betty Anne Voss'|
|Parents:||'Lady Louise' x 'Shinnyo No Tsuki'|
|Habit:||Dense low, 12" 10 years old|
|Foliage:||Very dark green|
|Flower:||3" H in H Petaloides Wavy, Opens Like a Rosebud Appears Double|
|Color:||Rhodamine Pink 62A RHS Color Chart|
|Date of Bloom:||6/3/71 5/31/73, 5/25/74, 5/29/76, 5/23/77|
Each year an independent description is recorded without reference to that of the previous year. In this way, variations between seasons are noted.
Having created a superior cultivar, the next thing is getting it known and accepted. My approach to this was to obtain the cooperation of some of the best known arboretums and growers. This would not only expose these cultivars to the public but would give some idea of their performance in various parts of the country. Cuttings and small plants were distributed from New England to Georgia and later to Oklahoma. There appeared to be little interest in evergreen azaleas in the northwest. Softwood cuttings ship well in plastic bags, and cutting material has been successfully sent as far away as New Zealand Australia and Switzerland.
To get distribution, I had to learn to root cuttings. On my visits to various nurseries, I found a rather wide range of practices. This was particularly true of the propagating medium. Some used pure sand others pure peat or perlite - but most used a mixture of peat and sand or perlite - usually in a 50-50 mix. They were all successful so it would appear many different mediums can be used if a few rules are followed: drainage is very important but the medium must be capable of holding moisture without becoming soggy; it should be porous; no fertilizer, either natural or synthetic, should be used.
My best results have been obtained with a 50-50 mixture of peat and coarse perlite. This is sterile, weedless, clean to handle and readily available. It is sufficiently soft so that roots can readily penetrate and expand. After the medium is put into place it should be compacted lightly with a brick- and then thoroughly watered and allowed to settle for a few days.
For cutting material - only new growth should be selected. It is best gathered early in the morning when the material is turgid. I have successfully rooted cuttings as early as June 6 and as late as Christmas. As long as they can be kept from wilting, the azaleas will root. The earlier cutting appears to root more quickly and, of course has a longer growing period. While a misting system is helpful for the cutting taken early, it is not necessary for those taken later- say in July. A shady location and watering once a day (greenhouse) is all that is required.
In preparing cuttings, I take new growth about 1 to 1½ inches in length - shorter if necessary - depending on the growth. After the bottom leaves are removed, the cutting is dipped into Rootone. I use this powder because it may help speed rooting, and does not harm. Azaleas usually root well without any hormone. In sticking the cutting, I make a hole with a pencil so the Rootone is not brushed off. Then I insert the cutting about ¾ inch deep. Resist the temptation to push the cutting deeper since this will encourage rot. The most important thing I had to learn was that the medium must be in intimate contact with the stem. To assure this, after the cutting is in place, I surround the stem with my thumb and two fingers and give it a good poke. This simple operation has improved my success markedly. Using these procedures, I obtain almost 100 percent rooting.
In the winter I seek a warmer clime for four months. I leave the cuttings in the medium during this time while a kind neighbor waters once a week, whether needed or not. With the porous medium, there is no danger of over watering. The thermostat in the greenhouse is set at 40-45 degrees F., and good growth is evident since by April the ball of roots has become almost fist size.
The rooted cuttings are now ready to be put into benches filled with Cornell Mix and spaced in 4 inch rows. They grow there through another year. In December, they are fed very sparingly with Osmocote 14-14-14 for extended slow release feeding about some three months. If I have insufficient space in the greenhouse to accept the plants, I put them into a lath frame with only fair results. Tender plants will be killed and heaving from late frosts, is a problem. Generally, I have found young plants are tougher than usually thought.
If you have no greenhouse, I recommend an article by Alfred Fordham that appeared in the July 1972 issue of Arnoldia, the bulletin of the Arnold Arboretum. It is entitled, "A Simple Frame for Softwood Propagation", and I have tried this frame in the open with considerable success.
As I watch plants grow, I tend to set up hypotheses to account for what I have observed. One such hypothesis is that plants are adaptable if given sufficient time to adapt to new conditions. A good growing plant maintains a balance between that portion above ground (foliage) and that below ground (roots). If the balance is upset, the plant attempts to restore that balance. For example, when a cutting is prepared for rooting, it consists of a bare stem with a few leaves but not roots. It is out of balance. To restore balance, it begins to send out roots and above ground growth is retarded until enough roots form to support the foliage. Then above ground growth will start.
When a plant is heavily sheared, the balance is again lost - too many roots for the amount of foliage. If left alone, the plant will attempt to strike a balance by growing more foliage and presumably retarding root growth.
For the last two years, I have been potting up my young plants rather than planting in outside nursery beds. This requires less work and is much easier to manage. When in pots, the plant becomes an individual to watch, more so than when in a bed crowded with a number of clones. I now put the two year plants into 6 inch plastic pots filled with fine pine bark. Since the bark contains little or no nutrient, I add a small pinch of 5-10-5 fertilizer for quick growth and a pinch of Osmocote 14-14-14, a slow release fertilizer that will probably last about three months.
To control insects, I have a program for outside plants. The first spraying is done just as first buds show color and the second after the flowers have fallen. I use Malathion, 150 ml per 10 gallons. If mites are suspected, I add Kelthane, 1 teaspoon per gallon. So far I have found little evidence of petal blight but I am considering preventive spraying. Dr. G. Lewis has written an excellent article on this, "Petal Blight - A Threat to Us All". Azaleas require little in the way of fertilizers. Ordinary 5-10-5 appears to be as good as the higher priced specialty brands. I scatter this over the plant by hand in dry weather and there is no sign of leaf burn. I estimate that one 50 pound bag covers about 10,000 square feet. It is never applied after the middle of July since new growth would have insufficient time to harden off and this growth would be killed back during the winter.
A number of materials can be used for mulching, such as pine bark, pine needles, wood chips, chicken litter, and oak leaves. The natural fall of oak leaves in the autumn is sufficient for established plants, but small azaleas may be smothered. I prefer pine bark, if available. Never use peat moss since it forms a thatch and does not allow water to reach the roots. I think mulching is more effective in the summer than in the winter; although mulching small plants helps to keep them from frost heaving.
A form of mulch which practically eliminates weeds while conserving moisture has been used successfully for the last four years. After planting, I cover the whole bed with newspapers, about three pages thick. Over this I place mulch material to hold the papers in place and to give the beds a pleasing appearance. This practice has been effective for four years so far.
Do not prune or shear the original seedlings from crosses. It is important for the hybridizer to see the natural growth habit. Older established plants, however, can be sheared as severely as yew or privet. There is no need to cut at a node - two or three new shoots will appear near each cut.
The foliage of so called evergreen azaleas varies considerably in the retention of evergreen appearance during the winter months. This depends on the cultivar as well as the season. Some are almost deciduous in appearance, while others seem fully evergreen. Evergreen azaleas have spring leaves and summer leaves. Those that grow in the spring are larger and less persistent. The summer leaves are small and appear at the terminal of the branch, but are more persistent, remaining throughout the winter.
It is important that plants have a pleasing appearance during the long period between blooming seasons, and this is possible with many evergreen azaleas. Plants with a low growing, dense plant habit and attractive, persistent foliage can rival Ilex crenata or some of the boxwoods as foliage plants, with the added bonus of a beautiful blooming season. And, depending upon the weather, many azaleas have attractive fall coloration, another landscape asset.