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Journal American Rhododendron Society

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Dr. Glen Jamieson ars.editor@gmail.com

Volume 51, Number 3
Summer 1997

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Germination and Growth of Seeds from Russia
Donald W. Paden
Urbana, Illinois

        A unique opportunity to observe the germination and growth of rhododendron seedlings developed in January 1996 when William C. Miller III of the Azalea Works in Bethesda, Maryland, received a fairly large quantity of seeds from Dr. Igor Smirnov in Moscow, who either collected them or arranged for their collection. There was no pre-arrangement concerning the disposition of the seeds, and Miller distributed some from each of the species to a number of persons living in various parts of the United States with no restrictions on how they were to be handled. The seeds were from nine species of Rhododendron. All of the recipients were experienced rhododendron growers, who chose differing conditions for germinating and growing them. This report of their observations within the first year of growth provides some comparisons among the species and the conditions under which they were grown that may be interesting to other growers, especially those just getting started in rhododendron culture.
        Each of the recipients of seed was invited by the author to comment on how the seeds were handled and to report on the growth of the seedlings approximately five months after planting. The persons who participated were: Larry Brown, Hammond, Louisiana; Barbara Bullock, Washington D.C.; Sandra McDonald, Hampton, Virginia; Don Paden, Urbana, Illinois; George Ring, Bent Mountain, Virginia; and Herb Spady, Salem, Oregon.

Observations of five of the participants on germination are presented in Table 1. All of them used sphagnum moss, possibly with some perlite added, upon which to lay the seed. As can be seen, none of the seeds for two of the species germinated. This failure was probably due to improper handling of the seeds before arrival in the United States: the seeds may have been too old, perhaps kept at the wrong temperature, or were affected by some other unfortunate condition. Results of the other species varied, with Rhododendron caucasicum performing the poorest and R. mucronulatum showing the best results. The findings suggest, however, that if growers start out with enough viable seeds they can expect to get seedlings.

Table 1. Success in seed germination reported by five participants.
  None Poor Fair Good
R. brachycarpum 5      
R. camtschaticum 5      
R. catawbiense     2 3
R. caucasicum 3   1 1
R. molle ssp. japonicum   1 2 2
R. luteum   1 1 3
R. mucronulatum     1 4
R. schlippenbachii   2 2 1
R. sichotense   1   4

Growth of the Seedlings
An examination of Table 2 shows marked differences in growth among species. There is also variation in growth reported by different participants for specific species. Paden's growth rates are listed in Table 2 both at three months and at nine months. Rough averages for each species are shown in the last column, with Paden's findings excluded.

Table 2. Growth of seedlings in inches reported by participants after several months.
  3 5 6 7 8 9  
  Paden* Brown* McDonald* Ring* Spady Paden* Average**
R. catawbiense 1 2 1 2 4 1⅓
R. caucasicum     1 1 1
R. molle ssp. japonicum 2 1 2 3 3 6 2⅜
R. luteum 1 2 2 1 10 1⅔
R. mucronulatum 2 2 2 2 3 2 2
R. schlippenbachii 1 1 1 7
R. sichotense 1 2 2 4 8 2⅜
* Also contributed information about germination.
** Does not include Paden's data for 3 and 9 months.

Comments of Participants
On Germination and Growth
Don Paden*: In central Illinois the Russian seeds were sown on peat moss. Upon germination, the seedlings were transplanted to trays with peat moss as the sole medium. They were grown under fluorescent lights, 16 hours per day, in a basement with fairly constant temperature. Other seedlings (not reported here) were planted on peat, perlite and a bit of compost but were not kept under lights. At the end of five months their growth averaged less than half that of the seedlings grown under lights.

Sandra McDonald*: In southeastern coastal Virginia the seeds were sown on a layer of peat moss overlaying some grower's mix. Since I can no longer find these mixes without fertilizer already added, I put plain peat or sphagnum peat over the other mix to keep the seedlings from burning from the fertilizer. After germination the seedlings were placed in a fine pine bark mix locally known as a soil conditioner, into which I also mixed some plain peat moss to help hold water in this fast draining mix. The seeds were germinated under fluorescent lights on 16-hour days in my home. After pricking off they were put into a cool greenhouse in the spring which is kept above freezing but can get high daytime temperatures.
        The seedlings in the greenhouse were under the mist system every day except on rainy days when it was turned off. Because I was away so much this was not a good year to care for seedlings. I find that rhododendron seed sown in December or very early January do better because of the hot temperatures we have. I seldom have good germination or growth for this type of seed sown after the middle of January. Most of the seeds seem to be species that do better in cool rather than hot weather.

George Ring*: (Bent Mountain, Virginia) Seeds were sown on the surface of a mixture of 75% sphagnum peat and 25% plaster grade perlite in an enclosed clear plastic shoe box. They were then placed under 24-hour fluorescent light. Temperature in our basement is consistently only about 65°F.
        Later, they were transplanted into the same growing mixture in the largest plastic salad containers obtained at Krogers grocery. Clear plastic lids were placed on the transplanted seedlings. The numbers of seedlings which were transplanted were recorded for each species (about 175 in total). After a few days under lights, the containers with transplanted seedlings were placed outdoors on the north side of the garage in bright shade except for brief periods of full sun in early morning and late afternoon. With the beginning of an extended period of rain in the area, the transparent lids were removed. This procedure is for people who are satisfied to grow plants slowly. It is simple, does not require much effort, and is quite economical.

Herb Spady*: (Salem, Oregon) Seeds were germinated on sphagnum peat under 16 hours of fluorescent lights at household temperatures. When the seedlings were about 1 inch high they were moved to Nearing frames where they required a minimum amount of attention. [The use of Nearing frames is described in David Leach's Rhododendrons of the World, 1961.] Growth in such an environment is slow compared with placing them under lights. (How can we be sure the seeds were not open pollinated?)

Barbara Bullock*: (Washington, D.C.) I use two mediums, sphagnum alone, and sphagnum and perlite. Both are very successful.

Final Remarks
A few remarks about the different species: British hardiness ratings for all the species was H4, indicating that they are hardy throughout the British Isles (but not necessarily in all parts of the United States). As indicated in The Rhododendron Handbook (Royal Horticultural Society, 1980), origins of the plants in the group include the Allegheny Mountains of the United States, Turkey, Scandinavia, Japan, Europe, Asia, Manchuria. Three of the species in Table 2, R. molle ssp. japonicum, R. luteum and R. schlippenbachii, are azaleas. In looking at the seedlings, their appearance can best be described as heterogeneous. Readers familiar with the different species will recognize the large leaves of R. catawbiense and the small leaves of R. caucasicum.
        It will be several years perhaps before these seedlings bloom. In the meantime it is interesting to know that there is a bit of Russia in our back yards.

* individuals contributing information for Table 1.

Don Paden, a member of the Midwest Chapter, has researched and written extensively on DNA fingerprinting of rhododendrons for the Journal.

by Anne Lawrence