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Posted by claire z6b Coastal MA on Sat, Jan 14, 12 at 11:40

Suddenly cones and buds become very interesting in this season (I don't want to think about last year's snow).

Icy cold is expected for the next few days - two nights bitterly cold and the day in between not much better. It occurred to me that some of the rhododendrons would be curling up their leaves for protection against the cold so I thought I'd take a few photos today before the curl-up. I didn't pay too much attention last year, and I have a few new rhododendrons, so I don't know if they all curl-up or just certain cultivars. I'll check tomorrow to see what happens.

Rh. Anah Kruschke (new this year)

Rh. Mary Fleming

Rh. Percy Wiseman (in his squirrel-proof cage)

Rh. roseum with Azalea Gumpo Pink at its feet.

Claire

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Posted by nhbabs z4b-5a NH on Sat, Jan 14, 12 at 20:01

I have a huge rhodie that I assume is Roseum Elegans (which needs pruning after bloom next spring) that has been here at my old farmhouse far longer than I have been. Since it lives by one of the kitchen windows, I use it to tell me the level of cold discomfort before I leave the house. I know from experience that if the leaves are curled, it will feel cold enough that I'll need a warm coat, hat and mittens before venturing out - no running out to the car in a light coat with my heavier coat (for walking to work later) in my hand.

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Posted by claire z6b Coastal MA on Sun, Jan 15, 12 at 10:20

nhbabs: That's a great use of a shrub as a temperature indicator! I have to rely on an electronic sensor swaddled in a jar, hung from my wisteria. Your kitchen window view must be lovely when the rhodie is in bloom. My Roseum was just labeled as "Rhododendron Roseum" so I don't know which one it is.

This morning the temperature was 10F; not cold for you northern types but chilly here on the coast.

Rh. Anah Kruschke leaves were a little curled, but not fully.

Mary Fleming, on the other hand, took the cold very very seriously and clamped the leaves shut.

Percy Wiseman is somewhat curled up:

and Roseum is tightly curled.

Tuesday and Wednesday are forecast to be much warmer so I expect all of the leaves to open up again.

Claire

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Posted by nhbabs z4b-5a NH on Mon, Jan 16, 12 at 10:04

My goodness what a range between the various rhodies. I only have the one rhodie at the house, but I will have to watch the ones down the road at the shop to see what they do in various temperatures. I know that they are all tightly rolled today as it is only a few degrees above 0.
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Posted by claire z6b Coastal MA (My Page) on Tue, Jan 17, 12 at 13:41

Not to beat this to death, but I checked the rhododendrons again today (temp. about 40 F). Cold? What cold?

Rh. Anah Kruschke

Rh. Mary Fleming (along with foxglove and geranium leaves)

Rh. Percy Wiseman

and Rh. Roseum

I am impressed, even stunned, by the rhodies' rapid adaptation to temperature.

Claire
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Posted by pixie_lou 5 on Wed, Jan 18, 12 at 15:23

Claire - I'm quite impressed with your documentation efforts. I on the other hand would never run out into the cold just to see if my leaves were curled.

I'm hoping to see a spread sheet soon - different varieties of rhodies and the particular temperature on which their leaves turn. Do you think wind chill and humidity make a difference? What about moon phase? This should all be documented on the spreadsheet.

I'm kidding of course. But I do find the whole phenomenom fascinating and I actually enjoy seeing your photo documentation.
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Posted by claire z6b Coastal MA on Wed, Jan 18, 12 at 15:51

pixie_lou: no way am I going to delve that deeply into the curly leaf phenomenon (spreadsheets? ...snort, snicker...) But I was very curious and I had to go outside anyway, to feed the birds, break the ice on the birdbaths, and get the mail, so I just hung the camera around my neck and shot photos along the way.

I also thought there might be some new gardeners who had just planted their first rhododendrons last season and who might panic when they saw the leaves suddenly curl up (oh no, did I screw up somehow? It's OK, rhodies just do that.)

There's a very nice article in the Arnold Arboretum magazine, titled "Why Do Rhododendron Leaves Curl?" by Erik Tallak Nilsen. For some reason I can't link directly to it (pdf) but It's the first hit if you google Why Do Rhododendron Leaves Curl? Apparently not just a straightforward response to cold, but also protection from bright sunlight in the cold and also prevention of too quick thawing of the leaf.

Claire