"English Roseum" is tough as old boots. My guess is that it was not established enough to withstand the very low temperatures you had this past winter.

Last winter was extremely hard on rhododendrons because of the cold and high winds. All rhododendrons do not reach their maximum hardiness until 3 to 5 years after planting. English Roseum and Scintillation are/will become very hardy. Purple Passion is advertised as Z5 hardy but has never done well for me at all even though it has never experienced anything below -10. If you're seeing tightly curled brown leaves, you may have to prune back to live wood. Wait a while longer to do this, though. Rhododendrons have remarkable powers of recovery.

There are a couple different but similar plants called Scintillation in the trade. I am in SE PA also and one of my Scintillations gets sun burned leaves in the summer and the other one doesn't. I think they are probably different clones.

Unfortunately rhododendrons and azaleas take a couple years to establish their full hardiness, azaleas take longer than rhododendrons. Field grown B&B plants are much hardier initially than container grown plants which are much more common today.

Wait until you see the new growth and cut back any parts that died during the winter.

True enough about more than one Scintillation. The hardiest form is the one sometimes listed as Gem Gardens Scintillation. There is no Gem Gardens nursery. The GEM stands for Gustav E. Mehlquist, long time rhododendron expert and hybridizer at the U. Of Connecticut. Originated in his garden and the name became corrupted. Like many Dexter hybrids, there are likely several versions of Scintillation in the trade.

Thanks all. My Scintillation has large, round-ish leaves, making it look sort of tropical. It did the best of all four of my rhododendrons. One more I have is Pink Roseum. That one appears to have lost all the previous year's new growth, probably did the worst of all, but is also closest to the street and probably gets more wind.

Along with the huge flower trusses, the leaves of Scintillation are one of its most desireable characteristics. For many years I have been growing an unregistered (as far as I know) hybrid of Scintillation and the species williamsianum. It is a bit bud tender, but the leaves are nearly as round as williamsianum and as large as those of Scintillation.

It's interesting you all talking about a lack of hardiness from newly planted specimens. That sure would explain the loss of my Extraordinaire that I planted last season. Interestingly enough, I also planted a Frank Galsworthy rhodi and that had no issues. Both were wrapped with burlap and they are about 15' from each other. I'm going to leave the Extraordinaire to see if it sprouts anything but I'm pretty sure it's fried. I guess since the Frank Galsworthy made it, it will likely make almost any winter. I just hope my buds are all fried on my Sappho like they were last year. Even my Polar Nacht rhodies experienced some limb loss due to the cold and they've been around for several years and sailed through last year with no issues.

As listed in Greer's handbook, there's a 10 degree hardiness difference between Frank Galsworthy (-15) and Extraordinaire (--5). Extraordinaire would be a stretch for Z6b even years after planting - I believe there is some of the notoriously tender Rothschild hybrids in its background. Ihave grown Frank Galsworthy for some years and have not found it easy. Prone to branch dieback and the flower buds seem to be extremely sensitive to cold once they begin to swell - odd since it is a late bloomer. -15 is pretty optimistic, too. -10 (maybe) is more like it. I have been growing rhododendrons in the same place for 30+ years and this past winter brought more damage than i have ever seen before. 50+ mph winds combined with very cold temperatures. Heavy wet snow breaking even stout branches. Those under the deep snow did well. Above the snow line, serious damage to even the toughest species and hybrids.

"notoriously tender Rothschild hybrids in its background"
In defense of these, I must note that in my admittedly milder (winter!) climate, 'Leo' held up rather well after 2 20-year winters in a row, and the buds have not fallen off, yet. My low was 1 F but, for perspective, the only standard Camellia japonica cultivar I have was badly burnt, though most of the stems should survive. And even 'April Remembered' had a bit of foliar burn. (yes, of course Leo is one of the hardier ones. No, I don't have a 'Crest'!)
Quick digression to repeat a story I've told elsewhere on gardenweb already: I have a Camellia 'Aida' in my garden; Longwood planted one a few years ago in a sheltered spot between the main conservatory and the production greenhouses. After winter 2013-2014, mine was scarcely damaged and even managed a few flowers. Theirs was killed outright, not even able to return from the ground although the researcher who planted it there gave it the whole summer to come back. The difference? I'd never fertilized my 'Aida' and my soil is probably rather low in nutrients. He had fertilized it to get it grow fast, I couldn't believe he got it from a rooted cutting up to a 4' plant in only 3 years. I think that's roughly the time period he implied. So, BLEs can't be spoilt with 'care' and expected to survive tougher than normal winters.

NOT that I think you would do that akmainegrower!!! I just think it's a very telling story, and confirms what I've always thought was true about plants in marginal climates. They have to be grown hard.

Ahh yes the Frank Galsworthy is more hardy than Extraordinaire. I had forgotten about that. Well that is certainly proof of the hardiness then. I think I may have lost a single branch on it. I hear you about tough to grow specimens as my Polar Nacht plants experience frequent dieback. If it's not phytophthora in the summer, it's winter kill. They do plod along though and always seem to make it. I guess the Frank Galsworthy will be another needy specimen. The Polar Nacht always bloom though so their buds must be tougher. I've been gently squeezing some buds between my fingers the last couple weeks to see if they are burnt out. Overall, I don't think they are as bad as last year although I'm worried my Sappho won't bloom again for the second year.

Hardiness in rhododendrons is a fascinating and complex subject. David Leach who probably did more to create hardy rhododendron varieties for North America than any other individual, held that there were really three types of hardiness: resistance to fall temperature drops, resistance to absolute midwinter cold and resistance to late spring frosts. All of these are genetically determined but strongly influenced by siting, patterns of rainfall/irrigation, plant nutrition, protection from sun and wind, among many other factors. Then when you consider that the species from which all hybrids derive occupy a vast geographic range ( in most cases) and huge variations in altitude, another level of complexity emerges. Pioneer rhododendron growers like Joseph Gable and G.G. Nearing grew 1000's of seedlings in an effort to find the hardiest.

david28rt: There are some hardy Rothschild hybrids, but considering the vast scale upon which his breeding program operated in the early 20th century,relatively few. That is no dispargement of what was accomplished. Many, maybe most, of the hybrids are incredibly beautiful. They just are not well adapted to anything very different from the benign Exbury climate.

As for "growing hard", this is not likely to actually increase the hardiness hardwired into a plant's genes. What i think is more likely is that more exposed locations trigger the mechanisms the plant uses to prepare itself for winter earlier in the season so they achieve full dormancy before the onset of serious winter. Net effect is the same is the same as increased hardiness:better chance of survival.

As for g

If there is dieback of the last year's growth (tan-brown drooping leaves and tan stems), is it still possible to get blooms this year?

I might be wrong but if it was cold enough to kill leaves, then the blooms are likely lost. On my rhodis, it's often the case that the blooms are more easily affected than the leaves.

mainegrower,
I think we are basically agreeing but saying it different ways.
Yes of course every plant has a predetermined absolute minimal temperature of survival. Growing conditions can't change that. But above that, and it some cases well above it, is a temperature range where, as you say, all these factors like "siting, patterns of rainfall/irrigation, plant nutrition, protection from sun and wind" come into play.
In the case of a plant grown hard, it had to build an extensive root system to find both food, and water in times of drought. (which were plentiful here in 2010, 2011, and 2012...and for all of which my 'Aida' was in the ground) It seems too obvious to even suggest that a plant with a more extensive root system is going to fare better in the dehydrating scenario of a colder than normal winter. It's too late to do a necropsy of the Longwood plant...and I certainly wouldn't have sacrificed mine to science, but I bet if both had been dug up we'd see that mine, though only 2-3' tall, had a bigger, wider root system than their 4-5' plant that was a couple years, at least, younger. I remember after the first drought in 2010, basically saying to the plant, "deal with it, no more drip hose for you." The soil here probably stayed moist in the deeper layers, so maybe it grew down more than the plant at Longwood had to, too.

Without providing details because I don't want to "trash talk" another horticulturalist, it has come to my attention that there's another folio of evidence of this after last winter, in this case applying to rhododendrons. Basically, someone lost a lot of plants that did just fine in this winter for me. This person loves to fertilize heavily. The slight climatic difference cannot possibly account for such a difference in outcomes.

If nothing else, if you use those so-called slow release beads, they can't magically only release nitrogen in the spring. They are going to release nitrogen all year whether the plants need it or not, and especially whether or not it's a good or a bad idea for them to be dosed with nitrogen at that time of year. The waxy bead matrix might actually open up a bit more in summer, in response to warmth...but, again, autumns are warm and sunny around here compared to Europe. it's going to keep releasing nitrogen until October at least.

davidrt28: I agree completely about the dangers of excessive nitrogen. Nothing makes a rhododendron more vulnerable to cold than late soft growth. Size of root system is to my mind a bit more iffy, at least for rhododendrons. The complex chemical changes that allow rhododendron roots to withstand temperatures that would kill many other plants really should not operate any differently in a large root mass than in a smaller one. Root depth is a possible factor, but both it and size of the mass would seem to have more to do with withstanding summer drought and increasing nutrient uptake than winter survival.

m_a and sequ: Flower buds are more likely to die from cold than other parts. Chances are a branch with brown drooping leaves has died, either from cold and exposure or some other cause. You can try peeling a bit of the bark to check a green cambium layer. If you find one, wait a while to see if the branch puts out new leaves. If none, best to prune out the whole branch. In any case, no bloom this year.