Baby , it ’s cold out of doors !
How cold?you involve .
So inhuman that my rhododendrons have fainted .
Your heart stops beating for a second if you don’t know about this natural phenomenon.
As I was wait outside the window of my home office on a particularly glacial January day , I noticed how the leaves of my rhododendrons were all droopy , like a collection of small umbrellas . Over the next duo of hours , the farewell started curve inwards ; and by late afternoon , they were hang like weird large green attic .
I ’m not particularly good at read nature sign , but I bonk this meant it was very very cold outside . It might just be the wintertime equivalent of that summertime temperature gauge when you break off an egg on the sidewalk during a heatwave just to see if you may fry it .
It was n’t the first prison term I find this happening to my rhododendron , so I knew on the dot what was going on . But it was the first time I thought , hmm , mayhap I should tell others , just to void the “ assistant , my plant life is dead ” panic , specially for our reader who are new to growing rhododendrons .
Your heart stops beating for a second if you don’t know about this natural phenomenon.
Why are rhododendron leaves curling inwards in the winter?
This reaction to below zero temperature is called thermonasty .
Thermo obviously indicate temperature , while “ -nasty ” stands for “ nastic effort , aka a works movement in response to a input . So thermonasty is a social movement in reply to temperature .
But why does it happen in rhododendrons?
One of the skilful feature of rhododendrons – and why they ’re an excellent shrub option for any garden – is the fact that they ’re evergreen . Their foliage will remain the same coloration whether it ’s the centre of winter or the top of summer .
However , there ’s a catch :
In the cold season , rhododendron do n’t involve as much brightness for photosynthesis . And this unconscious process slows to a halt when the temperature dips below freezing .
The rhododendron leaf curling gets gradually worse the colder it gets.
But rhododendron still have their canopy of leave on , which will still act like solar panels , even when the plant has no consumption for solar energy . If the plant absorb this solar energy , it will fire up up and melting . Then it will freeze out again at dark when the sun is gone . Then heat up and thaw again the following twenty-four hours . And so on . This diurnal freeze - warming cycle would be very detrimental to the cellular structure of the farewell .
So for protect themselves from engross too much light when the temperature is too scummy , the farewell draw in in on themselves . The less aerofoil exposed to light , the in high spirits the chance of surviving the freeze unscathed .
In addition to this , let ’s commend that rhododendron , in their aboriginal habitats , grow as an understory – one bed below the tall jacket crown of trees . They do n’t take as much sunlight . In the cold-blooded season , there is no tree canopy to protect them from the sun . So they require to protect themselves .
The curling is the downside of being evergreens.
In other words , they do n’t curl up to stay lovesome – like people do – but to stay shaded .
The curling of the rhododendron leaves is getting worse!
It may calculate like it ’s give way from bad to defective , but it ’s just a rude adaptation to how cold it is . The nastic movement in rhododendrons is not an immediate flop , but a gradual movement that start with the umbels lowering ( like the windup of an umbrella ) at about freezing temperature ( 32F or 0C ) .
When the temperature reaches about 25F ( about -4C ) , the single leaves will start to curl inwards , like little wetback . Then at around 20F ( around -7C ) , the parting will be fully rolled up .
A cocksure side - effect of this response is that it also makes it harder for crank and snow to gather on the leaves . Since the folio are both pendant and convex ( not to mention course glossy ) , the blow slides off faster than it would off a insipid horizontal surface .
On a really cold day in February.
Will my rhododendrons recover after winter curling?
Good news ! Yes , they will recover . As soon as the temperatures climb again , the rhododendron leafage will uncurl . That ’s because the thermonasty is a two-sided leaf movement . Once the stimulant is gone , the leaves discontinue responding and go back to their common shape .
Will rhododendron leaf curling affect flowering?
Another piece of good newsworthiness ! No , the curling of the foliage due to low temperature will not have a noticeable effect on future blooms .
However , there may be other cause why your rhododendron are n’t blooming . Have a face at this clause , in which I explain in more detail the most plebeian reasons .
Are there any other plants that curl in cold weather?
Have a look at how the leaves of my camellia shrub were curl up when the thermometer dipped to below freeze . Just like rhododendrons , camelia are evergreens and grow as an understory in their lifelike home ground .
It ’s the same chemical mechanism at play , although there are more studies about rhododendrons . ( Seriously , just type “ thermonasty in rhododendron ” in Google Scholar and you ’ll be amazed at the number of studies done . )
And just like with rhododendrons , the curling of the leaves did n’t affect the subsequent blooming of the camellia .
A positive side effect: the snow doesn’t accumulate in a thick layer.
Which is even more surprising , since camellia shrubs bloom much in the first place in the twelvemonth than rhododendrons . Have a expression at the beautiful flowers opening up less than a month afterwards on the same shrub . Is n’t nature awful ?
So to summate up , the rhododendron go away curling in the winter due to cold temperatures is just nature ’s way to accommodate . Just conceive of it as one more trial impression that the garden is still alive and transforming during the cold months .
The same rhododendron, a couple of days later.
The same rhododendron, perfectly happy and blooming in May.
My camellia was also curling at the same time as the rhododendron.
It still bloomed about three weeks later. The leaf curling doesn’t affect blooming.
