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 Rhododendron rex 
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Joined: Wed Feb 13, 2013 11:56 pm
Posts: 382
Location: Seekonk, Massachusetts USA, USDA zone 6b
Post Rhododendron rex
I recently received a Rhododendron rex and rex ssp. ficto. I live in coastal Massachusetts, USA USDA zone 6b. Where in the garden should I plant these? I think southern exposure may kill them and northern exposure may be too cold with deep soil freezes. Any tips?

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Last edited by Tim B on Sun Mar 24, 2013 2:57 pm, edited 1 time in total.



Sun Mar 24, 2013 11:27 am
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Joined: Tue Oct 02, 2012 3:52 am
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Location: bandon, oregon usa USDA climate zone 9a
Post Re: Rhododendron rex
nice plant and a possibly really sticky wicket concerning placement in your climate. guessing that this plant is not any more hardy than hardier selections of magnolia grandiflora and if you don't have good success with this or similar broadleaf evergreens (?) you will have trouble with this plant as well. if you are indeed doing well with broadleaf evergreens then treat it more or less the same way you normally do. if you do not, my suggestion is that it should probably be planted away from cold winter winds to protect the foliage from drying and freezing and with a heavy mulch to protect the roots and lower stem from freezing. southern and western exposures may get too warm in summer and northern and eastern exposures too cold in winter :cry: you might consider a planting position that has some kind of overhead cover thru a mixture of deciduous and evergreen trees to give some kind of protection against cold. maybe wherever you plant it you should consider placing a temporary shelter over the plant on really cold nights combined with whatever mulching and siting you do employ. hopefully, some of the above may be of some small interest or help to you or better yet someone will offer better advice. good luck.

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Sun Mar 24, 2013 12:08 pm
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Location: Maryland, USA
Post Re: Rhododendron rex
FWIW, when Ron tried a bunch of R. rex at Rarefind, they died. I mean, over 100. But they were small seedlings. Most died in summer and what didn't die in summer died in winter.
I bought a gorgeous large plant in person and brought it back to the east coast. It was killed by the horrid summer of 2011, where there was a long drought and heatwave, then almost 40 inches of rain in 40 days during the period surrounding Hurricane Irene. (we additionally had some huge thunderstorms both before and after it) It was the rain that killed it though, not the heatwave per se: the heatwave sets the stage of too-warm soil, but the phytophthora couldn't really go berserk until that hot soil get wet. This is what happens to most of these rare high elevation Chinese and Himalayan rhodies south of about Newport, RI. Har har. You see, you are just about right on the line. There might be a couple on Long Island, and there was one for a few years at one of the old collector's gardens outside Philly. But with global warming that line is just going to move northwards. (BTW a couple smaller ones I mail ordered had survived a couple winters, but were also killed in 2011)

The solution is either to: move to the PNW, or move to Cape Cod. Anywhere north of there will be too cold in winter, anywhere south of there too warm! And you would need massive wind protection on the Cape, like a south facing building courtyard. You might be OK if it has an absolutely perfect site: that sort of wind protection, and just the right kind of shade to keep summer soil temps down. Maybe cage it its first couple winters and wrap the cage in something transparent. The wind is what will suck those leaves dry. Another solution in areas that are mild enough in winter - and I like to believe that I am - is horticultural: I'm attempting to root and raise a bunch of phytophthora-resistant rootstocks, and learn how to graft sensitive rhodies onto them. I have my first couple experiments going right now - fingers crossed. The ones that tend to die from phytophthora: almost anything yellow (including Capistrano), anything big leaf other than R. calophytum, any species whose elevation range is high and isn't hybridized to something like R. catawbiense.

"southern and western exposures may get too warm in summer and northern and eastern exposures too cold in winter"
right that's why he would need a southern exposure with high deciduous shade, but early morning winter evergreen shade. Like I said, only in the perfect situation...and even then he's going to need a lot of luck. BTW George the all-time record highs on the tip of Cape Cod are actually about the same as the greater PNW. That explains why an Austrocedrus chilensis was once found growing there, but probably wouldn't be found anywhere south or north of there on the east coast. OTOH, though all time record lows are only a little worse, winters are overall MUCH, MUCH colder, windier, more destructive to BLE plant material...which explains why the area does not look like the PNW. Still, I was pleasantly surprised to find some clones of Ilex X altaclerensis at one of the Newport estates. Proof that even up there, the Atlantic has moderating effect if you're right on the water. You certainly wouldn't find those in a place like Springfield, MA.

Also there's a guy in CT with a bunch of hybrids between big leafs and things like R. brachycarpum ssp tigerstedtii. I think he trades sometimes with a guy in Nova Scotia. I'm sure he's nice but I'm not in the mood to ingratiate myself into the rhododendron mafia to try to wheedle a few cuttings from him. I'd rather just wait until Rarefind tests something like that and decides to commoditize it, even if that means I'll pay through the nose for it. Still too many variables in terms of whether they will really be tough enough to grow this far south. I can be a lot more muggy than coastal CT. I do own 'Hardy Giant' but I do not believe its purported 50% rex parentage is correct. I think it's just a bold form of R. fortunei.

BTW - the Polly Hill Arboretum doesn't list R. ficto/rex but they seem to have good experience growing rarer species there. You might contact them to see if they've attempted to grow big leafs and find out what happened if they did.


Sun Mar 24, 2013 2:06 pm
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Joined: Wed Feb 13, 2013 11:56 pm
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Location: Seekonk, Massachusetts USA, USDA zone 6b
Post Re: Rhododendron rex
Hi George,

I have been growing Magnolia grandiflora 'Edith Bogue' since 2004 without any issues. The 'normal' forms of southern magnolias will typically get heavy burn in our area. I'm also growing Aucuba japonica without any issues and the Aucuba is planted in a north facing position. I have 2 forms of Illicium (red and white flowered). Both are facing east and perform very well in my climate. I have a Eucalyptus debe planted in a south facing position (super hot in summer) and it performs well. The leaves do have some winter burn after this winter. This Euc has only seen 2 summers and 2 winters so far.....not much of a test yet but I am surprised it survives facing south against a 6' tall wood fence........it get hot there.

How much heat can they take in your area? Excess heat is a concern of mine. We probably get 5 to 10 days where the high temperature will exceed 90F (32.2C). Will this be a problem? Our average day time high for July is about 83F (28.3C).


Sun Mar 24, 2013 3:06 pm
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Joined: Wed Feb 13, 2013 11:56 pm
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Location: Seekonk, Massachusetts USA, USDA zone 6b
Post Re: Rhododendron rex
Hi David,

thanks for all the great insight!

How small were Ron's R. rex's? First year seedlings? In what position did he plant them (south facing, north facing, etc..)?

In what position did you plant your Rex's? My parents live in Rockville, MD and their heat is nothing like ours (they are hot). We typically get 5 to 10 days where it will hit 90F and our average high for July is 83F. Will planting the Rex in a south facing position kill it up here?

I can easily keep the wind off the Rex for the first few seasons.....I currently do that for my Citrumelo, Yucca carnerosana, Yucca linearifolia, one of my Yucca rostratas, Tetrapanex, Trachycarpus 'nainital' and Washingtonia filifera. Here's my Citrumelo in a cage/poly wrap.

Image

I don't think phytophthora will be an issue for my climate......perhaps it will. We generally have cold soil temps and our summers are much shorter than Maryland's. Are you having success with grafting Rhodo's?

How large are the 'hardy giant' leaves? Who sells hybrids with Rex or other large leaf Rhodos?

I guess my biggest question is how much summer heat can Rex take assuming phytophthora is not an issue??


Sun Mar 24, 2013 3:24 pm
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Joined: Wed Feb 13, 2013 11:56 pm
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Location: Seekonk, Massachusetts USA, USDA zone 6b
Post Re: Rhododendron rex
Hi David,

I just checked our temps for July 2011 and we had 4 days which hit 90F or higher that month and our average temp for that month was +2.8F higher than 'normal'. Hottest days in order were

101F
92F
91F
90F

You guys (Regan National Airport) had 25 days which exceeded 90F......wow.

104F
102F
102F
99F
99F
You get the picture :shock:

Your Rex actually looked OK after that heat? How much direct sun did it receive?

PS, our nightly temps typically drop below 70F here.......we only have a few nights per season where night temps remain above 70F.


Sun Mar 24, 2013 3:42 pm
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Joined: Tue Oct 02, 2012 3:52 am
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Location: bandon, oregon usa USDA climate zone 9a
Post Re: Rhododendron rex
Tim, heat is rarely a problem in my area near the coast where 75f is considered a warm day (LOL but true). our summers are very dry but the lack of heat generally keeps established plants from being stressed especially if they have some afternoon shade and mulch around the base. good to hear that you are having some success with broadleaf evergreens (especially the eucalyptus) BUT my concern that larger leaved evergreens like rex (which is likely NOT a form selected for extra winter frost hardiness like your magnolia variety was) are at extra risk for dehydration/wind burn in dry cold periods during the winter (or hot dry periods during the summer) because of the very size of their leaves (=larger evaporative surface). David's comments on the apparent necessity for being in a maritime dominated location like cape cod in your general area are probably depressingly germane for your plantings. the (relatively) mild but wet winters and definitely cool and dry summers in our nominally USDA 9a climate are pretty much perfect for lots of the big leaved rhododendrons---rex, fictilacteum, sino-grande, basilicum, macabeianum, etc,---and a number of other evergreen trees and shrubs (as long as they don't require summer heat to grow) as opposed to your more bracing 6b. nevertheless, without brave folks like you experimenting with various plants in various places in various ways, nobody can say for sure what certain plants might do in less seemingly hospitable places. hopefully, you will have success with this and other plants, prove the "experts" and nay-sayers wrong and beautify your garden (while astounding your neighbors). good luck. George

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Sun Mar 24, 2013 4:58 pm
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Location: Oxford UK
Post Re: Rhododendron rex
I've seen Tim's garden and I am mind boggled by what he can grow there... His hybrid Yuccas are state of the art :mrgreen:
May I suggest at least some shading over the plant during hot spells if you plant in a warmer part of the garden. Try to mimic the conditions the plant enjoys in its own natural surroundings. :D

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Sun Mar 24, 2013 8:35 pm
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Location: Seekonk, Massachusetts USA, USDA zone 6b
Post Re: Rhododendron rex
Thanks George & Andy,

I think I'll plant one rex in a northern exposure against my house which has a basement (which will warm the soil a bit) and another rex at an east facing position which is against a 6' tall fence which will protect against afternoon sun and cold winds from the west and northwest (our coldest air direction). I plan to protect them at least the first 2 seasons in winter. I will likely place lattice shading over the east facing specimen to keep that area cooler in summer.

Is there a difference between R. rex and R. rex 'ficto'?.......for growing conditions? Is one more tolerant to cold or heat?

PS, George here's a photo of my Eucalyptus debe after this winter......I think the stems are fine but the leaves are highly damaged.

Image


Sun Mar 24, 2013 9:42 pm
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Location: Maryland, USA
Post Re: Rhododendron rex
Tim,

I don't know what size Ron tried but since he is generally adept at growing out crosses and has produced many himself, I'm sure they were appropriately sized to allow for general survival. Seedlings at Rarefind start in the bathroom, move to an off-limits greenhouse, and finally to the field. He was hoping there would be an outlier that would be tough...there wasn't! (IIRC he had collected seed himself in SW China, or knew who had.) I have seen many of their hybrids growing out in the field, and in fact I "rescued" a plant Hank was going to throw away that I believed had some merit.

George - minor nitpick but I wouldn't quite call coastal Oregon "perfect" for these plants. Maybe only compared to the rest of the US. (wow, I'm the semantic nit picker recently) You have no summer rain, but so much fog the plants can just coast along (no pun intended) during that period. Nothing really dries out when days are <= 70F and foggy every morning. HOWEVER I have no doubt they would grow faster in their native haunts, where summer monsoon rainfall is 10-20 inches per month. Certainly, in the US the area from about Santa Cruz up to Coos Bay are the only places the plurality of big leaf series species (falconera and grandia) can be expected to thrive. The hardiest are OK up to coastal BC. Interestingly they even grow in upper Sonoma County, which is a climate I would somewhat more enticing...if they are watered in summer of course. The thing being even though they average in the 80s in the summer, the nights are still in the upper 50s so the roots will stay cool if mulched. As with Coast Redwood, the myth that these plants would _need_ constant fog is incorrect. They just need constant moisture.

Tim you will probably be OK for a few years in terms of summer death. Capistrano seems OK in coastal New England; south of there, certainly in NJ & PA, it is subject to "sudden death after reaching apparent maturity" which my plants - the largest rhodie I had - tragically suffered last year. I'd almost rather have something like R. 'Norph' which just summarily dies the first time it encounters a hot humid summer. My concern is when New England has an unprecedented heatwave followed by a Hurricane in August 2020, your then 5 footer kicks the bucket because of phytophthora. You're just not far enough away from the US SE to completely discount the possibility of having such weather shenanigans. Though, I recall from a drive from Boston to Newport RI that the soil looked sandy or rocky for most of the trip, so that should help you out in terms of avoiding root death. Maybe that's just what the highway fill looks like though.

As to the winter, you will have to protect for a few years to even give it hope of getting established. Once it has a strong enough root system, it will still need some wind protection but if you have one of the hardiest clones, known to have ridden out -5F or so in parts of Europe, I think it will at least have a fighting chance. R. rex vs. R. fictolacteum...one is considered hardier but I can't remember which. They are some of the hardiest of the various big leaf series.


Sun Mar 24, 2013 10:34 pm
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Location: bandon, oregon usa USDA climate zone 9a
Post Re: Rhododendron rex David and Tim
David, lets say "perfect" in the context of compared to most all other parts of continental north America (certain parts of the u.k. may be even better) and certainly compared to what Tim has to contend with. I also would say that "my" area really should include suitable spots from somewhere in ROUGHLY around the san Francisco bay area to somewhere in coastal b.c. Canada. once established (and this is important to note) in a SUITABLE area and properly mulched around the base, many of the "big leaf" rhododendron species will do fine in that area without summer water and of course even better WITH supplemental irrigation. that said, in optimum parts of their native monsoonal montane climate habitat they indeed can and should do better (if they don't get cut down for firewood or crop clearing there unfortunately). Tim, is "eucalyptus debe" shorthand for the beautiful and hardy species with the unspellable and probably unpronounceable (did I spell those words correctly?) last name aka e. pauciflora ssp. debeuzevillei ?? FWIW, my recollection from scanning david cox's "the larger species of rhododendron" (great book) is that some forms of r. rex ssp. rex MAY be slightly hardier than most forms of ssp. fictolacteum.

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Mon Mar 25, 2013 12:55 am
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Location: Seekonk, Massachusetts USA, USDA zone 6b
Post Re: Rhododendron rex
Hi David,

thanks for all the input. And yes, we have sand based soils in our area from the glaciers. There is no clay in our area. I've seen the soils in MD driving down RT 95 and they seem clay textured......totally different than our soils.

Hi George,

yes debe is short for debeuzevillei. There are 3 seed grown plants at that location. Perhaps one will prove to be hardier than the others?


Mon Mar 25, 2013 1:21 am
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Joined: Tue Oct 02, 2012 3:52 am
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Location: bandon, oregon usa USDA climate zone 9a
Post Re: Rhododendron rex
Tim, it's always the hope in "marginal" areas that seed of an "iffy" but desirable plant will produce a better adapted hardier individual and sometimes (thank heavens) something really good comes up---that's your hope with e. "dee" and my hope with some other species in the genus in my garden----e. saligna or globulus or robusta, etc., etc. wishing you good luck with the eucs, the rhodies, and all other plants you try. George

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Mon Mar 25, 2013 2:54 am
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Location: Leidschendam, The Netherlands. (52 N latitude)
Post Re: Rhododendron rex
Rhododendron rex in the wild get bassically winters with some snow and frost, but mostely on the dry side. But during summer they get soaked by the heavy monsoon and that keeps the temperature arround 20 to 25 C. R. rex is a Rhododendron you see in association with Trachycarpus takil. Autumn can be still warm and very sunny as the picture shows. In winter snow occurs there also now and then.

They flower in April in Nepal and Northern India. Well as it has a large distribution there is variability in hardiness I guess. For colder climates get the ones from the coldest provenance!

Trachycarpus takil and Rhododendron aboreum at a south facing slope, Kalamuni, November 9, 2011.
Image

And here a big Rhododendron aboreum with Trachycarpus takil arround it, Kalamuni area November 10, 2011.
Image

Alexander

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Last edited by Alexander on Fri Jul 11, 2014 2:14 am, edited 1 time in total.



Mon Mar 25, 2013 4:00 am
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Location: Leidschendam, The Netherlands. (52 N latitude)
Post Re: Rhododendron rex
Here a flowering Rhododenron aboreum in Nepal, April 26, 2010.

Image

Alexander

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Mon Mar 25, 2013 4:04 am
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