ABOUT RHODODENDRONS
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RHODODENDRON FORTUNEI & ITS CHILDREN
By Dr. Philip Waldman
Rhododendron fortunei was discovered in China by Robert Fortune
in 1856 and named after him. It was probably the first hardy species introduced, and it is
considered by many to be the finest Chinese rhododendron species. It makes an elegant
ten-foot tall specimen plant with broad oblong leaves of an attractive blue-green color
and a mounded habit which tends to be slightly open and tree like. The leaves are held
usually for two years and have a matte finish. The large 4" flowers, borne in May,
are white to pale pink, often with wavy margins, and have a delightful fragrance. The
trusses consist of 6-12" flowers, also of a solid texture and beautifully formed.
The plant is cold hardy to -15°F and also exhibits commendable heat
tolerance. It grows with excellent vigor and appears to be little bothered by pests. It
has become a very popular plant for hybridizers, useful for its many virtues as well as
being extremely fertile.
A particularly admirable form was used as a parent of the Loderi group
in 1901 which are considered to be among the best hybrids in England. These are vigorous
growing plants with huge trusses of extremely fragrant, trumpet shaped flowers of white to
cream to pink. Included among them are R. ‘Loderi King George,’ R.
‘Loderi Pink Diamond’ and R. ‘Loderi Venus.’ These plants have
received numerous awards.
Charles Dexter in Sandwich, Massachusetts used R. fortunei extensively
in his breeding program starting in 1922 and the "Dexter Hybrids" were
distributed widely, many as seedlings, especially on Long Island. There are hundreds of
Dexter hybrids that were named due to their hardiness, beautiful flowers, growth habit and
ease of culture. Paul Vossberg of Westbury Rose Company commercially introduced several
excellent Dexters in 1959, some of these selected by Howard Phipps. The new plants
included R. ‘Scintillation’ (one of the very best), R.
'Westbury,’ R. ‘Wheatley’, R. ‘Brookville,’ R.
‘Mrs. W.R. Coe’ and R. ‘Parker's Pink.’ Many other R.
fortunei crosses commonly known as "Dexters" are still gracing Long Island
gardens with their beauty. Popular plants include R. ‘Dexter's
Appleblossom,’ R. ‘Dexter's Spice,’ R. ‘Dexter's
Vanilla’ and R. ‘Dexter's Peppermint.’ Their fragrance enlivens our
spring season.
W.R. Coe in Oyster Bay grew many Dexter seedlings and some still are
seen at his former estate, now Planting Fields Arboretum. Among these are R. 'Mr.
W.R. Coe,’ R. 'Mrs. W.R. Coe' and R. 'William Coe.' Donald Hardgrove
used a hardy R. fortunei from Guy Nearing and crossed this with the tender yellow R.
wardii to produce many of his unusual multi-hued rhododendrons. Still popular are R.
’Golden Star’ (yellow), R. 'Amazement' (yellow) and R. 'Donna
Hardgrove' (orange).
Nat Hess in Sands Point was a strong supporter of R. fortunei in
hybridizing and was always commenting on its virtues. His enormous plant of R. fortunei
'Blue Cloud' was an awesome sight in bloom and was admired by many. Other R. fortunei
hybrids introduced by Nat included R. 'Dorothy Knippenberg,' R. 'Dorothy
Schlaikjer' and R. 'Long Island.' He also grew a plant of R. 'Hardy Giant, a
Knippenberg hybrid of R. fortunei and R. fictolacteum.
Other popular R. fortunei hybrids encountered in our gardens
include Paul Bosley's R. 'Brown Eyes, 'Joe Gable's R. ‘David Gable',
David Leach's R. 'Bravo' and R. 'Dolly Madison, Dorothy Schlaikjer's R.
'Nathan Hale' and R. 'Halesite Maiden,' Sain Everitt's R. 'Helen Everitt'
and the R. yakusimanurn-R. fortunei hybrids of R. 'Nestucca' and R. 'Little
White Dove.'
There are now thousands of different rhododendron varieties with R. fortunei
parentage in their genes and many others on the horizon. A wonderfully useful plant with
excellent garden ornamentality, R. fortunei will continue to give rise to many
children.
(This article was published in the 1998 Fall-Winter issue of New York Chapter’s
publication, Rhodora. Permission to use granted by the author Dr. Philip Waldman
and Co-editors Al Muller and R. W. Martin. Dr. Waldman has written several interesting
articles about other rhododendrons and their children, some of which can be seen on the
Internet)
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INSECT PESTS: RHODODENDRON BORER
Ian Donovan
What are the symptoms?Have you had a branch break off a plant from heavy snow load? Perhaps you've had a branch on which the growth seems stunted, or the leaves are yellowing compared to the rest of the plant, even dying. This flagging damage can be mistaken for Phytophthora dieback or similar fungal diseases. If the branch is cut across its diameter, you may find that there is a hole running inside the branch center. This latter damage is a certain indicator of a borer attack as it chews its way to the basal end of the branch. An inspection of the damaged branch will probably reveal occasional holes along its length with "sawdust", or frass, expelled from them by the larva. There may be roughened areas or discontinuous bark near nodes or the basal end of the branch.
Who did it?
The causal culprit could be a stem borer (Oberea myops) or
rhododendron borer (Synanthedon rhododendri). I've had borers attack big leaf
(elepidote) and small leaf (lepidote) rhododendrons, as well as deciduous azaleas. They
also attack mountain laurel. The latter critter is a native to Eastern US, very
destructive, and difficult to control. They usually form colonies among more mature native
rhododendron stands, and in garden plants. Damage by Synanthedon rhododendri larvae
is more likely to be found on older wood than the current season's growth. The stem borer (Oberea
myops) is a long horn beetle, which causes similar damage and has similar controls. It
has a different life cycle, however, so it will be addressed in a later note in this
series.
Synanthedon rhododendri is a clear winged moth in its adult
form. The 3/8" long body is blue-black, slim, and tubular appearing with three narrow
yellow bands circling the abdomen. Not often seen, it resembles a wasp more than a moth.
The span of the clear wings is only 1/2". They are active during the daytime in
contrast to most moths.
The adult moth usually emerges here in New England during a six-week
period from late May into July. Farther south, it emerges earlier, and into northern New
England its emergence may occur in late July. Its brief life is no more than a week. Upon
emerging the females emit a powerful pheromone to attract nearby males of the species. Egg
laying peaks during the first 3 or 4 days of the female clear wing moth's life. Eggs are
laid in bark crevices, branch crotches, or pruning wounds of host plants.
After a ten to fourteen day incubation, the larvae crawl on the surface
before making their entrance holes. Upon entry into the branch, damage to the plant begins
as the larvae become invisible and invulnerable to chemical control. The larvae begin
their journey down the branch toward the basil end where they grow to about 3/4" to 1
" long by autumn. The borer larva is easily recognized by the white body with a brown
head. It over-winters beneath the bark, completing the development in the spring. The life
cycle completes in one year.
Controls. Once you suspect that a rhododendron borer larva is inside a
branch, the only effective control is to cut the branch off below the larva and hole, and
bum it or cut the larva in half.
If you think you have a borer problem, knowledge of the borer's life
cycle is key to control. A good borer control spray program attacks the critter when it is
vulnerable and depends on: life cycle timing, weather conditions, and type of insecticide.
The moths are vulnerable to spraying of insecticides labeled for borer control once they
have emerged, as are the larvae before they enter the branch. Spraying should be done on
dry days and be heavy enough to run off all leaf and bark surfaces. This will
ensure that adults, eggs, and surface larvae are contacted. Systemic sprays, if labeled
for borers, may also be used.
Timing is best determined by using sticky traps baited with the
appropriate sex attractant and placed near infected plants. Traps should be in place 2
weeks before the first moths are expected to emerge. Male moths begin emerging before the
females and eggs require at least 10 days to incubate. Spraying need not begin until 10 to
14 days after the first capture in the trap. One good spray application, properly timed,
may last the season. Once the larvae have tunneled beneath the bark, they are invulnerable
to contact sprays.
Researchers are developing a spray to apply nematodes that will more
environmentally friendly and less toxic to non-targeted insects. Ask your local garden
center for availability of this new product. If you find information about this
forthcoming product, share it with us.
Ian Donovan iand@gis.net
(From Massachusetts Chapter Newsletter, April 1999. Permission to use granted by Ian Donovan.)
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By Harlie Peterson
At March 1999 Monterey Chapter Meeting, Monterey Chapter member Harlie Peterson tested the knowledge of the members about rhododendrons. Now it's your turn: the quiz is below.
1. The word "rhododendron" comes from the Tibetan meaning "mountain
flower" T or F
2. Rhododendrons come under what division of Plantae?
a. Thallophytes
b. Bryophytes
c. Pteridophytes
d. Spermatophytes
3. As a "class" Rhododendrons are Dicotyledons: T or F
4. An example of a soil pH rhodies prefer would be:
a. pH 5.5
b. pH 3.6
c. pH 7.6
d. pH 8.7
5. The ARS Convention was held on 4/27- 5/2, 1999 in:
a. Aberdeen, Scotland
b. Lhasa, Tibet
c. Bogota, Columbia
d. Bellevue, Washington
6. Lynn Watts is of ARS.
a. Treasurer
b. Secretary
c. President
d. Executive Director
7. The "Family" of rhododendrons is:
a. Rosaceae
b. Ericacae
c. Cruciferae
d. Compositae
8. A 20th Century "rhody" plant hunter in China is:
a. Rock Hudson
b. Sir Addlington Winesap
c. George Forrest
d. Aza Lea
9. The genus Rhododendron can be divided into several groups, two are:
a. Acutes and Glabrous
b. Lepidote and Elepidote
c. Undulete and Viscid
d. Ciliate and Cordate
10. Rhododendron(s) lindelyi, edgeworthii, and fortunei are noted for their:
a.hardiness
b.ability to tolerate alkalinity
c. fragrance
d. disease resistance
11. Indumentum in rhododendrons means:
a. bell shaped flowers
b. sharp pointed leaves
c.species difficult to hybridize
d. brilliantly colored hairy of woolly coatings of the leaves
12. The terms compact, dwarf, prostrate and tall refer to:
a. hardiness
b. color of leaves
c. habit
d. seed propagation
13. The seeds of a hybrid azalea will produce plants identical to that seed-bearing azalea. T or F
14. A rhododendron propagated from plant tissue is known as a:
a. clone
b. ligulate
c. strigase
d. Kleenex
15. Which one of these is not a red hybrid?
a. Jean Marie Montague
b. Fragrantissimum
c. Halfdan Lem
d. Markeeta's Prize
16. Which is not a blue-lavender hybrid?
a. Unique
b. Anah Krushke
c. Colonel Coen
d. Midnight
17. Which is not a yellow hybrid?
a. Horizon Dawn
b. Elizabeth
c. Lemon Mist
d. Saffron Meadow
18. Which is not a pink hybrid?
a. Antoon Van Welie
b. Christmas Cheer
c. Inheritance
d. King George
19. Which male and female parts go together?
a. stamen, anther, stigma; ovary, style, pollen
b. ovary, anther, pollen; stamen, style, stigma
c. stamen, anther, pollen; ovary, style, stigma
d. stamen, style, pollen; ovary, anther, stigma
20. One of the causes of chlorosis (yellowing of the leaves in rhododendrons) is:
a. Potassium deficiency
b. Sun scald
c. Phosphorus deficiency
d. Iron deficiency
(This quiz was seen in the April 1999 Monterey Bay Chapter Newsletter. Permission to use was granted by Harlie Peterson and Editor Phyllis Cole.)
The answers are at the end of this page. Go To Answers.
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Every person who has a rhododendron in the garden will want to look at this site. The materials and conditions are for people from the state of Washington so use with caution for your area. Check out the Washington State Website for Rhododendron Problems.
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[A. Richard Brooks, past ARS president, answered a question to a reader about her sick rhododendron. I thought it should be shared. Editor]
I am writing to ask for information and help for our rhododendron. I noticed the leaves were curled. Now a few weeks later they are brown and falling off. Is this due to lack of water? Or a number of things? It's in the open, under a pine of an oak tree. It gets very windy. In the summer it is in partial shade. Never had a problem with it in 11 years. It is huge, about 7 feet tall and about 7- 8 ft across. Today I am raking, and will water, and fertilize it, along with other plants. We live in Grafton, MA, Zone 5. This past winter was strange. Not much snow, but we did have rain. This spring is very, very dry. I think it was the worst in about 48 years. I don't want to loose this beautiful bush. Someone suggested picking off the buds.
Your help will be greatly appreciated.
Sincerely,
Betsy Rondeau
Dear Betsy,
Betty Spady has forwarded to me your query about a not-too-happy rhododendron. It's difficult to diagnose from a distance what might be the problem, but here are some possible causes for the curling and browning of the leaves:
You mention advice from someone to pick off the buds. I think they may be referring to what we call "deadheading", which is picking or cutting off the faded flower head, to prevent the formation of seed. Supposedly, this channels the plant's energy into forming new growth and buds for next year, rather than into setting seed. If your plant has done well without this operation in the past, I think there's no need to change--i.e., "if it ain't broke. don't fix it".
I hope this has been of some help.
Dick Brooks,
Concord, MA
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Are rhododendrons shade loving
plants? In their natural environment many rhododendrons grow and prosper in open
situations. However, those natural climates are often cool and misty places. Over the
years I have made some observations about rhododendrons and shade.
Rhododendrons respond to light like all plants. When grown in a dark
location they reach for light. Growth is tall and spindly and blooming is sparse. When
they do bloom, the trusses are large and the leaves are large. If you want to grow
show-winning flowers, grow your plants in deep shade.
On the other hand, when grown in full sun the growth will be short and
dense. Many terminals will have flower buds, but the trusses will be smaller. This
situation creates an ideal compact rounded landscape plant. Spring flowering will find a
plant covered with color. There is a caveat. Full sun does not mean on the south side of a
building or any other reflective surface. In that site there is a double dose of heat and
light.
All rhododendrons are not created equal. Some will tolerate full sun in
the mid-Willamette Valley even in a year as consistently hot as the summer of 1998.
Remember that does not mean full sun with inadequate water. Others do not like full sun
even during our cooler summers. On the other hand most rhododendrons will tolerate and
thrive in full sun along our coastal strip. There may be a few exceptions. The problem
there relates more to wind than to sun.
So you might ask, "Where do I plant rhododendrons?" If you
want a heavy flowering, tight and compact plant use a site that is as bright as the
variety will tolerate. If you are not familiar with the tolerance of the plant consult
someone who might know. Very few of us have an unlimited number of ideal sites, so you may
end up with some in too much shade and some in too much sun. Remember that those sunburned
leaves will be covered by flowers in the spring and will be hidden or fall off the next
growing season.
Ideal shady sites are ones with open sky but shade like the north side
of tall buildings or other structures. The shade cast by a tall tree is good. Plant
outside of the drip line of the tree and watch for dehydration due to competition from the
tree. Probably the next best site is filtered dappled shade provided by trees that are
openly branched. Here again, watch for competition from the tree.
One way to provide more light for your rhododendrons is to
"limb" your trees high.
Most rhododendrons are shade tolerant, not shade loving plants.
(From Willamette Chapter Newsletter, November 1998. Permission granted by author and editor, Dr. Herbert Spady. Dr. Spady gardens in Salem, Oregon, USA.)
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Article from Journal of Arboriculture. T.A. Chick and J. J. Kielbaso in their article, "Allelpathy as an Inhibition Factor in Ornamental Tree Growth: Implication from the Literature," Journal of Arboriculture, 24 (5), September 1998, 274-279, say that not all plants are compatible. Certain species produce chemicals that are toxic to other plants, a negative effect known as allelopathy. Among those listed in the article are rhododendrons and sumac (the chemical-producing species) that affect Douglas fir that is chemical-sensitive to those two groups. Red fescue, Kentucky bluegrass and Colonial bentgrass produce chemicals that are toxic to azaleas. (Seen in "Plants and Gardens," a publication of the Brooklyn
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Botanic Garden.)
TISSUE CULTURE
One of the methods of propagation of plants is by tissue culture. While this is not a method most people chose to use, it is still of interest. Dr. Wilbur Anderson did a great deal of the early research in rhododendrons, and he was awarded the American Rhododendron Society’s Gold Medal for those efforts. Now there are several nurseries that use tissue culture for some of their propagation. It is especially useful in getting new varieties on the market in a short period of time. Two interesting sites came to my attention, one by Ann Kyte and the other by her daughter, Kathy Liu. The sites are of particular interest to me because I knew Ann Kyte through the International Plant Propagator’s Society.
Ann Kyte was one of the early people to work in developing tissue culture laboratories. She worked in the Briggs’ Nurseries Laboratory in the early days of the Briggs micropropagation program before starting her own laboratory. Ann and her husband, Bob, served as volunteer consultants to tissue culture laboratories in Brazil and Egypt. In Brazil they were called in to provide advice for a two million dollar tissue culture lab which had some business problems. In Egypt they helped plan and start up an elaborate lab. This lab was sponsored by an agribusiness that had a well-established business structure and a built-in market for its products. With some persuasion she shared her expertise in the book, Plants from Test Tubes: An Introduction to Micropropagation, currently in its third edition. (Timber Press, 1996 $29.95). In addition to being a tissue culture expert, Ann is a Master Gardener. She tends a large garden and reads extensively in biotechnology news.
Kathy Liu, Ann's daughter, teaches biology at Westmoor High School in Daly City, CA. As a graduate student in botany, she used tissue-cultured plants to study plant fungal infections but has never used tissue culture with her students. "It is something that I have always thought that I would like to do, but I just haven't. Perhaps the insight shared here will give me the confidence to try it with a class or two." Kathy, along with Sue Black and Stan Ogren founded "The Gene Connection", San Mateo County (California) biotechnology education partnership in 1990. This partnership provides everything (equipment, supplies, reagents, training and technical support) for high school classes to work with DNA. Labs supported by this program include transformation, DNA isolation, DNA fingerprinting simulation, and others. The Gene Connections now serves all 21 public high schools in San Mateo County plus several private schools and two of the three community colleges. Kathy has been a teacher consultant with Access Excellence since its inception.
If you would like to read more about these subjects, you can connect to these Websites through Access Excellence. <http://www.accessexcellence.org>
Or you can connect direct to each Website
Preparation by Ann Kyte Preparation <http://www.gene.com/ae/LC/ST/st2bgplantprep.html>
Plant Protocol by Kathy Liu Plant Protocol <http://www.gene.com/ae/LC/ST/st2bgplantprot.html>
(Thank you for permission to use this information with modification and link these sites granted by Kathy Liu and Ann Kyte BWS)
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CUTTINGS
Fine Gardening magazine in the Q & A Column of Fine Gardening, page 12, December 1998 answers a question about taking cuttings of rhododendrons. Marlo Dohery, chief propagator at Twombly’s Nursery in Connecticut, gave a brief description of how the Nursery propagates rhododendrons. Check your library if you don’t have access to another copy.
Description of R.
canescens from University of Delaware
<http://bluehen.ags.udel.edu/udbg/shrubs/descriptions/r_canescens.html>
Description of R.
prunifolium from University of Delaware
<http://bluehen.ags.udel.edu/udbg/shrubs/descriptions/r_prunifolium.html>
Description of R.
schlippenbachii from University of Delaware
<http://bluehen.ags.udel.edu/udbg/shrubs/descriptions/r_schlippenbachii.html>
Description of R. minus
from University of Delaware
<http://bluehen.ags.udel.edu/udbg/broadleafeg/descriptions/r_minus.html>
Websites About Soils from National Gardening Magazine
Building Great Soil : Experts share their knowledge http://www.garden.org/redirect/soil.html>RETURN to TOP of PAGE
Thallophytes= algae, fungi, lichen
Bryophytes=mosses, liverworts
Pterophytes=ferns, horsetails, club mosses
3. True: Dicotyledons have two leaf seeds [Other class
is Monocotyledons, which has one leaf seed, such as grasses; see Kessell's Rhododendrons
and Azalea]
4. Ans. a. pH 5.5 [see ARS publication Fundamentals of Rhododendrons
& Azalea Culture; pH scale goes from 0 to 14; 7.0 is neutral, acid lower than 7.0,
alkaline higher than 7.0; in Aptos the average pH is 7.2]
5. Ans. d. Bellevue, Washington
6. Ans. c. President
7. Ans. b. Ericaceae;
Rosaceae=roses
Cruciferae=mustards
Compositae=dandelions, sunflowers
8. Ans. c. George Forrest, Leach's Rhododendrons of the World
9. Ans. b. Lepidotes (with scales), Elepidotes (without scales),
Kessell's Rhododendrons and Azaleas p.21
Acutes and Glabrous=sharpened and no hairs
10. Ans. c. fragrance, Kessell's Rhododendrons and Azaleas
p.122
11. Ans. d. brilliantly colored hairy of woolly coatings of the leaves,
Leach's Rhododendrons. of the World p. 30
12. Ans. c. habit
13. False: Mendel's Law
14. Ans. a. clone=identical to parent
15. Ans. b. Fragrantissimum=white
16. Ans. a. Unique=yellow
17. Ans. b. Elizabeth=red
18. Ans. d. King George=white
19. Ans. c. stamen, anther, pollen; ovary, style, stigma [mnemonic for
male parts: s-a-p]
20. Ans. d. iron deficiency due to high pH
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Your comments are welcome. Send your ideas to bettyspady@aol.com.
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