Some Of My Experiences in Hybridizing
H. L. Larson
In the late 30's I began a hybridizing program at the old Nursery. Since this was a very small nursery I was forced to thin out these plants rather quickly in selecting the best of them for future propagation. Among these first crosses were R. 'Loderi Venus' x R. griersonianum. The best plant of this cross has flowers almost the size of R. 'Loderi' and in a beautiful shade of pink with a deep red throat.
From R. 'Marinus Koster' x R. 'Snow Queen' three outstanding plants were raised. About the time this group of plants was about a foot high I needed some large understock and decided to use these seedlings as they seemed to be the least promising. Three plants however, were set out to be grown on and they have large flowers in a very tall truss. One of these is pure white, the other pink and the last is a light pink with a deeper margin. I have often wondered what the variations would have been if we had grown 75 of them to flowering size.
R. fortunei x R. 'Earl of Athlone' produced a plant with bright red flowers of large size and a fine truss. It is much hardier than R. 'Earl of Athlone' and can be propagated from cuttings. R. fortunei x R. 'Mme. Fr. J. Chauvin makes a fine rounded shrub with very dark green leaves and large pink flowers.
There is also a beautiful yellow rhododendron in the Nursery, a chance seedling which came in a group of R. souliei. It is presumed that some member of the R. campylocarpum group is involved in this cross. The flowers are quite large in a nine-flowered truss and are clear yellow without markings or spots of any kind. These are some of our first hybrids and most of them are now very large plants.
A cross of R. 'Albatross' x R. 'Pygmalion' has produced flowers of large size and in pink to rose shades. R. 'Romany Chal' x 'Pygmalion' produced a plant with large flowers and trusses with various shades of red and rose in each flower.
R. 'Dawn's Delight' x R. fortunei has produced a superb plant with larger and finer colored flowers than R. 'Dawn's Delight' itself. This plant is noticed immediately by visitors to the Nursery by its strange shade of pink.
At about the same time I made crosses of R. 'Dr. Stocker' x R. campylocarpum and R. campylocarpum X R. fortunei. These crosses were very satisfactory and equal to those made elsewhere.
R. 'Romany Chal' x R. griersonianum gave us a group of tall growing plants with good flowers ranging from bright red to almost maroon. These plants and griersonianum x R. 'Loderi Venus' are plants of top quality. Later other crosses were made using griersonianum as one of the parents and none of them were satisfactory and were destroyed.
At about this time it was decided to use one-fourth griersonianum in a few hybrids and R. 'Fusilier',' R. 'May Day' and R. 'Fabia' were used. R. 'Fusilier' x R. 'Queen of the May' gave us a plant with good flowers and truss in an odd shade of pink and the entire flower being speckled red. R. 'May Day' x R. 'Cornish Cross' seems to be quite variable. Two plants of the group have flowered to date, one a red, and the other white with a red throat. It seems that the R. griffithianum in R. 'Cornish Cross' was picked up in this plant. These plants will not be at their best for another year as they were injured in the freeze of 1955.
R. thomsonii x R. 'May Day' will flower this spring and we are looking forward to seeing it with interest. R. 'May Day' x R. 'Fusilier' has given us a low growing plant with almost double red flowers.
R. didymum x R. 'Diva' and the reverse cross growing near each other seem to be very much alike and I do not think it makes much difference which way the cross is made. The flowers on the plants are mostly very deep red with an occasional plant having bright red flowers. R. didymum x R. 'Fabia' also produces dwarfish plants with flowers ranging from almost black to bright red with more or less of a collar such as R. 'Fabia' has. I think these R. didymum crosses would be ideal where plants of medium size are required.
R. souliei x 'Fabia' produces plants that vary only slightly. A number of them have bloomed and all have fine yellow flowers of very thick texture. The only variation noticed is the size of the collar which it inherits from R. 'Fabia.'
We have a great many R. williamsianum crosses that should be reaching maturity in the next few years. One of these which seems to be flowering prematurely is R. williamsianum x R. arboreum roseum. There are six and seven quite large flowers in a slightly raised truss. I think the color would be considered a glowing pink. I have an R. H. S. color chart but it has been raining here for the past 33 days which makes it hard to use it out of doors.
I could also take a flower off the plant and check the color indoors but I would like to get a picture of it intact if the sun ever comes out.
Some of the small leaved rhododendrons were used to produce plants of a more dwarf nature. R. pemakoense x 'Racil' gave us plants which are now about twelve inches across by six inches high and covering themselves with quite large pink flowers. R. ciliatum var. bergii x R. calostrotum makes a slightly larger plant with larger flowers and is also a profuse bloomer.
In this article I have given a short description of some of the crosses which have flowered here. All of these are of superb quality and would be an asset in any garden. In the past several years I have been using the chance seedling which came in the R. souliei group as a parent as it has a beautiful yellow flower and fine foliage. It is used as a seed parent only. Crosses with it and R. 'Berryrose' var. 'Belvedere' x R. 'Jasper' will be in flower this spring and we have hopes of intensifying the color in the yellows.
From my own experience I believe that better results in color and form can be obtained by using one-fourth R. griersonianum with some of the older rhododendrons which have a high raised truss. By this I mean the use of such plants as R. 'Fusilier', R. 'Fabia', or R. 'May Day', as one of the parents and R. 'Queen of the May', R. 'Snow Queen' or R. 'Marinus Koster' as the other parent. The use of one-fourth griersonianum with some of the raised truss varieties would increase the chance of putting a top on the trusses of the new seedlings.
These are my own experiences and observations and I hope that they will be of some use to others interested in hybridizing.