How cold did you get?? I'm in zone 7 and it hasn't gone below 15 at my place so far. My Rh. fortunei is fine so far, bouncing back from every deep freeze. I didn't think it was considered particularly hardy and expected it to be marginal. Of course we haven't had the single digit temps since I got it so I shouldn't be too complacent yet.

I recorded a low of 8 degrees by my mini greenhouse. R. macabeanum, R. mallotum, and R. edgeworthia are all hardy to 5-10 degrees. They're still babies, and we hadn't had a hard frost yet when that first cold snap hit. Even the R. cinnabarinum, which I've had a long time don't look very good. I'll give everything until May or June, but I suspect some of them are goners.

The problem is you chose a bunch of kinds that are not hardy enough. There are lots more that are. Do you visit local large collections of them, such as the Rhododendron Species Botanical Garden? Hardly a shortage of interesting and beautiful kinds in such displays that do not burn up or freeze out every time it gets below double digits (F.).

When I used to go to local rhododendron society meetings in the 1970s a rhododendron hardy to 10 degrees F. was "tender" or a "California Special". Even in northern California there have been big freezes that wiped out kinds that they have been able to keep for very long periods in mild parts of Britain etc.

8F is a typical USDA Zone 8 low. The USDA zones are based on the

Average
Annual

minimum temperatures for specific 15 year periods and are not based on the lowest temperatures seen in the areas mapped, either during the 15 year period used or outside of that period. I've seen readings below 5F at least twice in my USDA 8 location, north of Seattle and less than 1/4 mile from Puget Sound.

Two of the most noticeable failures of evergreen shrubs commonly planted in this area that are on display this month are those of Cotoneaster lacteus and Magnolia grandiflora 'Little Gem'. Both have already been browned by the cold this winter. I saw the cotoneaster freeze all the way to the ground in 1990, labels and catalogs typically designate it at least USDA 7. Probably it is hardy to about 10F so then in the minds of those trying to sell plants that makes it a Zone 7 item, since Zone 7 is 0-10F, right?

In the case of the magnolia this is a repeat of severe damage occurring in 2008. Numerous properties around here are again sporting examples that look almost as though gone over with a torch.

I used to work at the RSBG, but I haven't been lately. My R. cilipense and my Mahonia 'Charity' look like hell, too. This is the coldest garden I've ever had. It's colder than the surrounding areas. It's warmer in the summer, too. It means I need a different plant palette. Live and learn.

I share your pain Hallerlake. I used to have a lot of R. cilpinense. Started them from cuttings. They turned into frozen toast years ago. As you say, "Live and learn".
My low so far this year has been 9 F. I live on a bluff above Maple Valley at 750 ft elevation. Haller Lake, in Seattle, must be in a frost pocket with poor air drainage at times.
Mike

Yes, both of those have a history of being damaged in colder local winters. I think 'Cilpinense' is yet another rhododendron that is thought to have a floor of about 5-10F. (Note that more than one clone has been grown under the name, perhaps these vary a bit - as do species rhododendrons, with different representatives sometimes ranging rather widely in cold tolerance).

More than one kind of Mahonia x media is showing some singing at this time. The 'Arthur Menzies' near what is now the Witt Winter Garden at the Seattle arboretum were turned to stumps in 1990.

It doesn't help that they're mostly in the corner that got run over last spring, and subsequently, had to be dug up.

I took a closer look yesterday. The Rododendron edgeworthia, R. mallotum, and the 'Cilpinense' are green below the snow line, so there's hope, but I may still have to rethink them. I don't want to have to worry about them every winter. They won't serve their function in my landscape if they die almost to the ground every year or so. R. strigillosum is hardy to 0 degrees. Maybe I should try that again. The trick will be finding decent sized ones that I can afford.

>R. strigillosum is hardy to 0 degreesNote, again that species rhododendrons vary in hardiness within the species. Even when named clones are on the market you are dealing with variation between these clones. I think P. Cox talks in one of his books (I am not near my library at the moment) about Rhododendron edgeworthii, for instance being as tender as 20 degrees F. in some forms.

The R. edgeworthia form I have is hardy to 5 degrees according to the RSBG