A Vireya Seed Odyssey: Some
Observations
Bill Moyles
from the Journal of the American
Rhododendron Society
Volume 55, No.2, Spring 2001
Germinating Rhododendron Seed
For the past thirty or so years I have been germinating and growing on
rhododendron seed and after thirty years I think I've gotten pretty good
at it. Probably because it is so easy! It has been my experience that
if one sticks to the typical lepidote or elepidote seed - and particularly
hybrid seed - it is absurdly easy. The seed is very forgiving. Collecting
and drying seed, and subsequent storing in the freezer, is quite straight
forward with no significant viability problems. I have always germinated
my ericaceous material on milled sphagnum in plastic-covered containers
under lights at around 60-70°F (15-21°C). No damp-off with sphagnum,
and the milled sphagnum decreases the problem of moss "over-growing"
the seed to just about zero. A real no-brainer for the amateur. The only
time I have deviated from fairly standard procedures was to experiment
with GA3 (gibberellic acid) to "break dormancy" with seed of
the Japanese species Rhododendron degronianum ssp. yakushimanum.
Yak seed was taking almost two months to germinate whereas most species
took around four weeks. I sprayed in some yak seed with (as I recall)
400ppm GA3. Treated seed germinated in less than a week. The control sowing
took over a month. But breaking dormancy is never really a problem with
rhododendron seed; thus no heroic methods are called for.
Section Vireya Rhododendrons as
a Special Case
I find the situation changes somewhat when one moves to germinating and
growing the seed of section Vireya rhododendrons, which is the
focus of this odyssey. It becomes a different and more challenging (and
interesting?) ballgame. The problem it seems to pose for the seed grower
is basically one of touchiness. It just seems to be more specific in its
needs and less tolerant of "sloppiness". Perhaps this is just
a reflection of its needs in general, as many vireyas are epiphytic in
nature and detest sogginess and bad drainage.
Becoming Hooked
Some years ago I became interested in vireyas. I happen to live in an
area where they can (with caution) be grown. Strybing Arboretum where
they were introduced to horticulture in this country became my hangout.
The head propagator at that time, Peter Sullivan (since retired), handled
the vireyas from Dr. H. Sleumer's early New Guinea collections and carried
on an extensive hybridization program in an attempt to create plants that
were more growable for the general public. Sullivan's original selections
still grow in a church garden in San Francisco and are probably the oldest
vireya (hybrid) specimens in the United States. They are considered by
many to be among the finest vireya hybrids available today. Vireyas were
then and are still a novelty and a challenge, but their amazing diversity
and unique beauty offer the rhododendron specialist an opportunity to
grow something very special. I became hooked.
Seed as a Way In
Having been an avid seed grower of traditional rhododendrons, propagation
by seed became the obvious way for me to extend my limited collection.
Actually it was the only practical way: you quickly find that it is much
easier to solicit and receive seed than cuttings! And, if you become interested
in hybridizing (as I did), seed rearing is a necessity.
Outside of Strybing, seed was hard to come by. At that time the American
Rhododendron Society seed manager in Oregon would send out what little
vireya seed she received immediately upon receipt. It had the reputation
of having a very short shelf life, and it was thought that stored seed
would not germinate. Not very satisfactory if you run a seed list. This
point of view really didn't encourage seed collection and distribution,
and as a consequence seed availability was limited. Strybing through its
international contacts and its own material was about the only reliable
source.
Fortunately, through Strybing, I was put in touch with John Rouse at the
University of Melbourne, Australia. Because of its benign climate and
proximity to New Guinea, the Melbourne area supports extensive vireya
cultivation. Rouse was and still is an internationally recognized collector
and grower of vireyas as well as a research scientist. Although not his
field of specialty he has investigated issues related to pollination and
germination of vireya seed. Over the years, Sullivan at Strybing had been
receiving seed from him and gave my name to him as a potential U.S. seed
"distributor".
My first seed from Rouse was seed that he had received from a Japanese
collector working in New Guinea. To my amazement it germinated vigorously.
I felt that this seed must have travelled around a good bit before getting
to me, and if that were the case so much for "limited viability".
I think that started it all, and I was encouraged to develop and maintain
a freezer full and circulate a list of stored seed.
Rouse was generous with his seed and was selfing many of the species in
his collection as well as making hybrid crosses. I began to solicit additional
seed from Australia and then New Zealand and eventually took over the
vireya seed distribution for the American Rhododendron Society. Over the
subsequent ten years or so of managing the vireya list a wide selection
of seed has been distributed ranging from the southern hemisphere to the
Royal Botanic Garden Edinburgh and Kew and from various private sources.
Graham Smith at the Pukeiti Rhododendron Trust in New Zealand was extremely
generous in his support. I no longer distribute seed for the ARS and John
Rouse is no longer active, but those who grow vireyas have pretty well
identified themselves and still receive seed. The Hawaii Chapter of the
ARS is now playing an active role in soliciting and distributing seed.
Vireyas from Seed (Or How To Do It)
Based on a good bit of personal observations and communication with others,
I quite naturally have come to my own conclusions regarding the handling
and germination of vireya seed. As noted above, compared with non-vireyas
their requirements seem quite specific, and I have tried to outline the
differences and similarities (as I see them) below. Obviously my conclusions
are untested in the classic sense and most must be prefaced by: in
my opinion ...
In the Beginning
Vireya seed should be collected only when pods are mature. That is when
the seed coat is sloughing and the pod is beginning to split. I have germinated
"green" non-vireya seed but have been unsuccessful with immature
vireya seed. All rhododendron seed dries easily and quickly at room temperature
or under gentle heat. It can then be sown immediately or stored. If stored
for later sowing or sharing it should go directly into the freezer. No
special treatment or desiccator is necessary. I am of the opinion that
freezer stored seed as opposed to refrigerator stored seed increases the
seed's shelf life.
The Germinating Medium
I germinate all my vireya seed (and ericaceous seed in general) on milled
sphagnum moss with perhaps 10 or 15 per cent perlite added. Seed is sprinkled
onto the surface of moistened (fluffy) moss and then sprayed in. The container
(say, a plastic cottage cheese container with drainage holes - a hot nail
does it) is then covered with plastic film, secured with a rubber band
and placed under fluorescent lights 4 to 6 inches (10 to 15cm) below the
tubes. Rhododendron seed requires light for germination. If the seed is
good, germination can be expected in three to five weeks. The moistened
moss may need spraying every two weeks or so, but 2 inches (5cm) of moss
assures moisture retention - a thin layer of moss over other media tend
to dry out too quickly.
The above seems to be standard procedure for most rhododendron growers
in non-tropical climates. In warmer climates, e.g. Hawaii, where 70°F
(21°C) is the average and humidity is high, germination on open benches
should work nicely. And I am sure that other germinating media would work
quite well. Shredded moss and fern fiber is a possibility. Unmilled sphagnum
seems difficult and overgrows the seed. Coconut fiber is most often cited
as an alternative. I have found it quite dense, but I am sure it could
be loosened up with perlite or sand.
I leave my lights on sixteen hours a day and try to maintain (for vireya
seed) an ambient temperature of 70°F (21°C). I have concluded that
the germination of vireyas is somewhat temperature dependent. That is,
non-vireya rhododendron seed germinates nicely at 55 to 65/70°F (13
to 18/21°C), but vireyas do better at the higher temperature. Sixteen
hours is more than sufficient for germination and sustained growth, and
I feel that it is unnecessary to purchase expensive full-spectrum tubes;
cheap cool white tubes are just fine.
Vigor and Viability
Hybrid seed shows the greatest vigor and viability - in general. I have
germinated hybrid vireya seed that has been freezer stored for ten years!
All seed is stored in the freezer and I go back into my "stash"
periodically now that I have discovered the possibility of germinating
quite old seed. What does one have to lose?
Wild collected seed often (not always) shows vigor similar to hybrid seed.
I am now annually testing seed of Rhododendron lowii collected
four or five years ago by a friend, Dr. David Binney (New Zealand), on
Mt. Kinabalu in Sabah.
This seed continues to germinate, and I have sufficient seed to carry
on for another (God willing) five or ? years. The lowii seed
is probably "hybrid" seed with overlapping populations of R.retivenium.
But that is another story.
To be expected, self-pollinating (most) cultivated species does not show
the same vigor or extended viability as does selfing (pollinating) with
a sibling. But some do. And some just poop out or produce weak children.
There is always a good deal of variation.
Quite understandably folks insist on getting seed of the "real thing",
but insisting on hand pollinated seed of the "best form" often
results in weak seed. Unfortunately many think that there is only one
"real" example of a species. And if I've got one I've got "it":
the "true species". Hard for folks to accept the population
concept of a "range of variation". It's that range of variation
that is most interesting.
Most of this variation is a matter of genetics. What is this "hybrid
vigor"? Assuming perhaps that much of the "species" seed
collected in the wild is in fact "hybrid" seed in the sense
that it results from the cross pollination of different individuals. The
only recent paper I have seen on vigor is John Richards' "The Genetics
of Vigor" appearing in the Bulletin of the Alpine Garden Society,
Vol.61, 1993. I highly recommend it.
This is not to say that technique and environment count for nought! It
is always best to do several sowings of the same seed lot at different
times and perhaps under different conditions.
Now That They've Germinated
Vireya seedlings are much slower to establish themselves than are non-vireyas.
Sometimes they will sit and sit in their seed pan until they decide that
it is okay to grow. Some may never make this decision. Again the differences
between hybrid and species are evident. Several potential seed growers
have left the fold because of this: "They just won't grow".
This recalcitrance is relatively easy to overcome by merely them to a
fresh medium and feeding a bit. Rhododendron growers will recognize this
as "Rule #1": if it isn't doing well just move it!
I go a bit further and move seedlings (1 to 2 sets of true leaves) to
a mix of 50 per cent perlite and 50 per cent milled sphagnum in community
plastic "trays" (6 x 10 in, 2 in [15 x 25cm, 5m] deep) that
are "hooped" with cane and covered with plastic film.
They look much like covered wagons. These are put back under fluorescent
tubes and the temperature inside the wagon goes up by virtue of the enclosure,
but humidity is maintained. A light (1/4 strength) foliar feed at 80°F+
(27°C+) in the wagon generally does the job. Sometimes growth is phenomenal.
I never lose a thing.
Coping With Success
After an inch or so of growth the hoops and covering can be removed (perhaps
a month or two) and then it's just a matter of space and your growing
environment. I move seedlings out of the lights into my protected conservatory
very soon. But they could be kept under lights for longer. Some do move
seedlings into individual (perhaps 1 in [2.5cm] square) containers and
grow them longer under lights. It's really up to you and your overall
growing situation.
Transitions can be touchy but small seedlings are very adaptable. I find
that a 1- or 2-inch (2.5- or 5-cm) seedling can be moved out of the seedling
mix and find its way in rougher growing medium very quickly. My rougher
mix consists of mainly of coconut chips, fine fir bark, perlite and bits
of rough peat. This can be in a flat in your greenhouse - any warm well
lit area - or into individual squares. The objective is always a well
developed and active root system. It is a mistake to think that you must
initially produce lush vegetative growth; it;s what's going on underneath
that counts.
The Big Question
How long does it take to bloom a vireya from seed? The answer is probably
an optimistic four to five years. The more vigorous plant will probably
bloom sooner and many later. Some growers feel that by taking tip cuttings
of 1-inch (2.5cm) seedlings and re rooting them in a peat/perlite mix
will in time produce blooms sooner. I know of no data that supports this
but certainly a tip cutting of a seedling roots easily and produces a
fine new root system in an enclosed high-humidity environment. This is
something the advanced grower can experiment with and is one way to cope
with a seedling's refusal to grow. It is amazing to take a tip cutting
from an inch seedling and see it root!
In Addition
For those interested, and even if you do not pursue your own seeding odyssey,
I would highly recommend seeking out a paper by John
Rouse: "The Propagation of Rhododendron Section Vireya From Seed"
(see Notes From the RBG Edinburgh, 1985, Vol.43:1, pp99-115).
I feel that Rouse's paper is essential background reading: pollination,
seed production, storage, germination, growth processes, the works - and
quite readable for the non-botanist.
Growing on to Maturity
Vireyas love warmth, but I think it has to be shown that they do not need
to be treated as a "tropical". Obviously they must be protected
from freezing and if protected they will grow nicely in a temperate clime,
e.g. here in the San Francisco / Oakland Bay Area and most of coastal
California. Admittedly they grow faster where it is warmer year round
but they do quite well here. Vireya hybridizers are now having some success
breeding material that will take 25°F (-4°C) for short periods.
This work is being extended (see below re: R.saxifragoides) and
evaluated.
Fortunately vireyas take well to containerizing. They can be grown in
boxes on patios and back porches and easily moved in and out during winter.
They can be experimented with as "house plants" and as hanging
baskets in a conservatory. Where the climate supports it they take readily
to growing in protected raised beds where sharp drainage is assured.
But however grown some essential conditions must be met:
1. They should be grown in a rough fast draining mix - medium to rough
fir bark, coconut chips, redwood fiber, rough perlite or pumice and some
chunky peat where available. Really any "chunky" mix avoiding
traditional loamy soil. Always keep one eye on drainage!
2. If containerized they should never be overpotted. In fact, a potbound
plant is probably to be desired as long as fast drainage is maintained.
It's really a matter of aesthetics and the balance between plant characteristics
and container.
3. Periodic weal fertilizing will be necessary. Gypsum can always be applied
as well as Epsom Salts to maintain a calcium magnesium balance and acidity.
4. Vireyas seem to do well in strong filtered light - full sun is probably
to be avoided. But the appearance of your plants will tell you and some
colors just do not look attractive in too much sun.
In Conclusion
Establishing an effective technique for raising seedlings opens one up
to sampling the fantastic variation within this section of the genus,
and I will close with one example that has given me great satisfaction:
In the early 1990s, Os Blumhardt (New Zealand) contributed several hybrid
seed lots involving R.saxifragoides as one of the parents. Rhododendron
saxifragoides is a dense cushion forming shrub growing in New Guinea
at 9,000 to 12,000 feet (2,700 to 3,600 m) and is on every collector's
list of most wanted. Rhododendron saxifragoides itself has proved
difficult to grow, but we now see (thanks to Blumhardt) that its hybrids
grow well and retain its dwarf characteristic. And, in addition, coming
from such a high altitude one also hopes for a bit more tolerance for
cold temperatures. Thanks to the Blumhardt seed Jim Gerdemann in Yachats,
Oregon, is pursuing the hardiness issue with the saxifragoides
hybrids and other parents, particularly R.commonae in both its
red and cream forms. I am just having fun growing a spectrum of dwarf
bonsai-like pot plants. I am now crossing several clones and siblings
and using them as parents crossed with larger flowering vireyas.
The criticism is often hears within traditional rhododendron circles that
hybrids never really have that "species look". I do not think
that this is necessarily the case with vireyas. They are so diverse and
can be combined in so many ways. You are able to create your own new "species"
with that distinctive look. And seed raising is the only way to do it.
I have tried to keep the above "instructions" generic and they
should be read more as guidelines than anything else - nothing is hard
and fast. Fortunately rhododendrons set copious seed and the seed stores
well in the freezer. Experimentation costs little.
Reproduced by kind
permission of
The American Rhododendron Society
©
ARS
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