Rhododendron Leaves in Winter
Why do rhododendron leaves in winter look shriveled and weird? The answer comes in two parts, and both of them are interesting, and perfectly normal.
By John G. Stamos
Table of Contents
Rhododendron Leaves in Winter: An Intro and a Little Background
So, a few weeks back, I’m kidding around on X (the former Twitter) with a bunch of my pals about the scrunched-up, shriveled, less-than-majestic appearance of my rhododendron bushes in the cold wintertime temperatures here in my garden’s hardiness zone of 5B/6A. (The crude, unavoidable comparison involves certain parts of the human male anatomy and the way said parts respond to a solid drenching in an ice-cold shower. You get my drift.) To make a long story short, rhododendrons don’t look so great when it’s cold outside, and I thought it’d be sort of funny to snap a pic, shove it out there on X, and make a comment about it. Then, after I’d actually done those very things, I started thinking that it would have probably been more interesting and useful to explain why cold-hardy bushes of the genus Rhododendron end up, at least appearance-wise, in the grip of such a sorry state of cold temperature affairs. I mean, I actually know why shivering rhododendrons look like the plant world’s equivalent of a pair of shriveled men’s… well, you know. But instead of laying that knowledge on them, I offered my good buddies up a perfunctory, pejorative comment at the expense of my cold and lonely rhodies. You see, years back, when I first saw my rhodies react to cold weather in this unflattering fashion, I got a little worried about them and decided to bone up on the subject. And what I learned was pretty amazing. It’s the info that I should’ve shared with my buds on X a few weeks back but didn’t. The good news is, I’m sharing it with my buds in The RGG right now. And here we are.
In this article, you’re going to get the fruits of those years-ago research labors of mine, along with some new info I’ve gleaned through my ongoing obsessive reading, and from my continued observations of my own garden’s rhodie population. You’ll learn exactly what rhododendrons are actually doing that makes them look like shriveled and shrunken human male junk, you’ll learn why they’re doing it, and you’ll also learn why they’re not doing it (some tradionalist thinking is gonna get shot down right there). You’ll get some beyond-excellent product recs, and you’ll get the article’s bibliography/”For Further Reading” list. Plus, you’ll get a bunch of color photos, sprinkled throughout the article, that you can use to check the appearance of your freezing rhodies against mine (and put your mind at ease just in case the whole shivering/shriveling thing has got you freaked). Finally, you’ll get a link to The RGG YouTube Channel vid, “Why Do Rhododendron Leaves Droop and Curl in Winter?”, starring yours truly as host and narrator. This article definitely has got the rhododendron wintertime goods, boys and girls.
So, let’s do this. Let’s learn about rhododendron leaves in winter, and why they look and act the way they do during that coldest of seasons. Here you go…
Rhododendron Leaves in Winter Behaving Badly: For the Record, It's Called Thermonasty, It's Completely Normal, and It's Two Things in One
Thermonasty defined.
Ok, so we know that rhododendrons (and not just plants in the genus Rhododendron, but also members of certain other genera in the rhodies’ plant family, Ericaceae,¹ like Pieris, for example) look pretty pathetic, all shriveled and shivering and such. This overall condition arises as a result of something called thermonasty,²⁻³ and it’s a form of leaf movement that occurs as a response to changing temperature conditions. In fact, the word “thermonastic” is a compound of two words sourced from international scientific vocabulary: therm, meaning temperature, and nasty, meaning movement.⁴⁻⁵ Unlike movements associated with tropisms⁶ (geotropisms, phototropisms, etc.) which are directional in nature (for example, in the case of a phototropism, the plant, and/or some or all of its aerial parts, are moving in a specific direction toward or away from light. In the case of thermonasty, however, a particular plant’s leaf movements are not directional. The leaves aren’t actively, mechanically moving toward or away from anything. They’re just responding to temperature.²⁻³ And in the case of rhododendron leaves in winter, they’re obviously responding to cold temperature. When a particular rhododendron looks the way it looks in winter, all shriveled and shrunken, it’s because its leaves are exhibiting the results of thermonastic movement. And the big takeaway for all of you concerned rhodie plant parents out there? It’s all totally normal and indicates that your rhodie bush is healthy and doing exactly what nature’s intended it to do.
Rhododendron thermonasty is really two separate movements.
Droop and curl. That’s what rhododendron leaves in winter do. And together, these two thermonastic leaf movements are what account for the rhododendron’s unhappy shrunken and shriveled wintertime appearance.*
Thermonastic droop. During the coldest temperatures of the year, each leaf on a particular rhododendron plant droops to an essentially vertical position. In the warmer days of spring, summer, and fall, each of a rhodie’s leaves are more or less horizontal in position and parallel to the ground. In the cold of winter, they droop almost completely down and assume a nearly perfectly vertical position. But remember, this movement is not directional – there’s no overriding attractant/repellent pulling or pushing those droopy, sad-looking leaves. They’ve moved entirely in response to a temperature change. Namely, the freezing temperatures of winter. You’ll get a little of the science behind this in just a bit.
Thermonastic curl. This is the second component of thermonastic action undertaken and displayed by rhododendron bushes and their ilk during the cold months of winter. Simply put, when it gets cold outside, rhododendron leaves start to curl, undersides inward along their longitudinal axes. And the colder it gets, the tighter they curl (more on this, including citations, a bit later). When it’s super-cold outside, those leaves look like long, hand-rolled cigarettes.
Given their effects on the appearance of individual rhododendron leaves in winter, it’s easy to see how these two thermonastic responses contribute to the overall shriveled, shrunken look of a particular rhodie bush spending its time out in the cold.
*I’m going to add something here with respect to thermonastic leaf-droop and leaf-curl that’s going to seem a sort of contradictory and confusing (but, hopefully, only a little). Remember that thermonasty implies leaf movement that’s not directional, and shouldn’t be consideerd the same as active, directional tropisms. Well, in the case of thermonastic leaf-droop and curl, it’s not incorrect to also think of this action as thermotropic.⁷⁻⁸ The leaves are drooping and curling (so “nastic” and “tropic” actually both do apply, since these actions imply movement), but again, are doing so in response to a temperature drop. They’re not mechanically moving toward or away from anything, as in the case of other plant tropisms. So, rhodie leaf-droop and leaf-curl, for all intents and purposes, can really be considered thermonastic AND thermotropic. But for the purposes of the remainder of this article, and for the sake of simplicity, I’ll refer to the phenomenon as thermonastic leaf-droop and thermonastic leaf-curl.
The Science Behind the Thermonastic Droop and Curl of Rhododendron Leaves in Winter: It All Happens at the Cellular Level
Why do they droop in winter? Thermonastic leaf-droop science (just a little, I promise).
The answer lies at each leaf’s cellular level.⁹ Rhododendron bushes start scaling their metabolisms back when the temperatures start dropping. While temperatures fall and approach freezing levels, rhododendron leaves begin engaging in thermonastic droop (and curl). By the time temperatures do fall to 32° Fahrenheit, all aboveground parts of a rhododendron plant are well on their way to being completely dormant, and by the time temps drop to 25° Fahrenheit, when the rhodie’s leaves have drooped as far to vertical as they possibly can, they are completely dormant. Finally, by 17.6° Fahrenheit, the plant’s aerial structures – leaves, stems, etc. – are frozen solid.⁸⁻¹³ When the rhodie is in this dormant state, it doesn’t – can’t – metabolize, process, or dissipate any of the energy from sunlight that it collects.⁹ In a plant’s leaf cells are organelles known as chloroplasts,¹⁴ which are responsible for the collection of sunlight and its subsequent conversion to food and energy for the plant. Within the chloroplasts are protein complexes called photosystems, which carry out the photochemistry component of photosynthesis, resulting in the absorption of sunlight and the transfer of energy and electrons – either incorporating it into the active plant’s metabolism as food, or dissipating it.¹⁵ Photosystem II is the first of these protein complexes involved in this process.¹⁶ When a plant, a rhododendron, for example, is active during the warm, sunny days of spring, summer, and early autumn, all of this goes off without a hitch. But in winter, in the grip of freezing temperatures, the rhododendron is dormant. But the chloroplasts and their photosystems, particularly Photosystem II, are not. These will continue to absorb sunlight and convert it to energy, even in cold temperatures. But, because the plant is dormant, there is no way for that stored energy to be metabolized or dissipated. At this point, the rhodie’s leaves are at risk of severe damage – damage coming directly from the sunlight that continues to be absorbed and converted to energy that cannot be metabolized or dissipated.¹⁷ Those leaves can potentially fry like bacon.
So, what does this have to do with the rhodie’s thermonastic leaf-drooping activities? Glad you asked…
Rhododendron plants, even comparatively large ones, are essentially understory plants – they commonly grow within the shade of overarching tree canopies during the warmer months of the year. This is exactly the case with the rhododendrons, azaleas, and pieris that grow in my garden, which is surrounded by an old-growth oak forest. During the warmer months of the year, the tree canopy that shades my rhodies and company is robust. But when autumn rolls around and temperatures start to drop, so do all of the oak leaves. And, just like that… presto! The tree canopy is gone, and so is all the rhodies’ shade. So, even though temperatures are colder as fall and winter grind on, the sunlight that hits my rhodies is actually more intense and longer-lasting. Again, even though it’s winter. So rhododendrons in winter are faced with two conditions: 1) Cold weather that makes them go dormant and unable to process the sunlight energy they collect in their chloroplasts, and 2) More sunlight, in terms of both intensity and duration of exposure…
Mmm mmm mmm! Can’t you just hear those rhodie leaves sizzle?
So, what’s a rhododendron to do in this scenario? Simple. It allows its leaves to drop in a nearly vertical position to avoid those direct blasts of sunlight, which it can’t metabolize or dissipate because of its cold-induced dormancy (again, it’s temperature that’s the impetus behind this phenomenon). Problem solved. Thermonastic leaf droop to the rescue!
So, are we good here on the leaf droop thing?
Okey dokey. We’re on to the next rhododendron leaves in winter phenomenon…
Why do they curl in winter? Thermonastic leaf-curl (a little more science).
As in the case with leaf-drooping, it’s what happens to rhododendron leaves in winter at the cellular level that drives the leaf-curling component of thermonasty.
Freeze-thaw cycles. In a nutshell, living plant tissues, when subjected to alternately freezing and thawing temperatures (freeze-thaw cycles), can experience damage that manifests itself at the cellular level. When plant leaf tissues freeze quickly, the ice crystals that form within their cells are small, and the potential for cell membrane damage is minimized. The more slowly plant leaf tissues freeze, the potential for cell membrane damage is greater due to the fewer but larger ice crystals that form as a result of the more gradual freezing. This is the mechanism that informs the process of flash freezing. But the really extensive leaf damage happens during the thawing process, particularly if that thawing occurs quickly. When a frozen plant leaf thaws too quickly, the ice crystals that have formed within its cells can easily pierce and damage, or even destroy cell membranes. It’s always far less damaging to a particular plant’s leaves to thaw at a slow rate.⁷⁻⁹, ¹⁸⁻²¹
Curled leaves thaw much more slowly than flat leaves. Rhododendron leaves engaged in thermonastic curling can roll themselves up very tightly. In fact, the colder the temperatures to which they’re subjected, the tighter they curl. And a leaf that is curled will open and become flat only very, very slowly as it’s subjected to warming sunlight and rising temperatures. Very simply, those frozen, curled rhododendron leaves expose less surface area to the sun and warmer ambient air temperatures, and therefore thaw much more slowly than plant leaves that remain uncurled and flat. And since the thawing process takes so much longer in a curled rhododendron leaf, the actual number of freeze-thaw cycles to which rhododendron leaves are subjected are minimized due to the simple fact that they stay frozen longer. So, rhododendron leaves engaged in thermonastic curling are protecting themselves from 1) The damage associated with a fast thaw, and 2) The damaging effects of more frequent freeze-thaw cycles.⁷⁻⁹, ²²
A note about one of this article's cited sources.
One of my cited research sources for this article (number 9 in the bibliography’s list of cited sources) is a short article in the Piedmont Master Gardeners Website and Blog, written by noted ecologist, plant expert, blogger, podcaster, and author, Matt Candeias. The piece is informative and easy to read, and it touches on all of the points in the article you’re reading here. I highly recommend reading it, and I highly recommend a visit to Matt’s wonderful blog (where the cited article initially appeared) and podcast, In Defense of Plants. Matt’s incredibly passionate about plants and gardening, and his research skills and expertise are renowned. Since I’ve only just ordered it and haven’t yet read it, I can’t yet officially recommend Matt’s book, In Defense of Plants: An Exploration into the Wonder of Plants. I’m sure, however, that once it ends up in my mitts, I won’t be able to put it down until I’ve milked it for everything it’s got. At that point, I’m beyond confident that RGG readers and subscribers will be receiving my full-on recommendation, and will be able to order it right here from within the friendly confines of The RGG. Stay tuned, boys and girls…
Shutting Down Venerable Misconceptions about Rhododendron Leaves in Winter: These Just Ain't So
There are a few long-standing, commonly held beliefs regarding rhododendron leaves in winter, and why they droop and curl when those temperatures drop. Unfortunately for their proponents, none are accurate. Below is the short list of rhododendron droop and curl apocrypha, along with the refutation of each one.
Misconception number 1: Rhodendron leaves droop in winter in order to minimize snow load.
The illusion. A lot of long-time gardeners, including many that I know personally, have been making this claim for years. Their take on the situation is that if a particular rhodie’s leaves remained in a horizontal position, parallel to the ground, snow would more easily accumulate on the plant and ultimately break its branches.
The reality. Nah. For one thing, if snow and ice is going to accumulate on a rhododendron, it’s going to do it regardless of whether the plant’s leaves are horizontal or vertical. There are plenty of surface details along the branches of a rhodie that perfectly allow snow and ice to collect.⁹,¹³,¹⁷ This statement has been field-tested by yours truly in my own garden, and with my own rhodies. When it snows heavily enough for accumulation to occur, it does so whether or not leaves are drooping or horizontal. Besides, rhododendron branches are resilient as hell. I’ve had massive snow drifts drop on my rhodies from the roof of my house, and those rhodies got buried. It would have made no difference whatsoever if the leaves were in a horizontal or verical position. Buried in snow is buried in snow. And again, rhodie branches are tough as nails. Can a branch or two snap if your rhodie gets blasted by a shit-ton of snow (particularly in the form of one, massive, consolidated plop from the roof of your house)? Sure it could. But it ain’t gonna kill your bush, and it would have happened regardless of leaf position. So, rhododendron leaves in winter do NOT droop to minimize snow load.
Misconception number 2: Rhododendron leaves in winter are curled in order to conserve water and prevent desiccation.
The illusion. People who take this position (and there are some really smart ones) believe that the general drop in humidity levels during the winter months is enough to send rhododendron plants into full-on water-saving mode. The belief here is that a curled leaf retains moisture by limiting certain aspects of transpiration,²³ primarily water loss, and the overall reaction by the plant to dry wintertime conditions is a curling of all of its leaves. There’s no water available in the frozen ground and in the cold, humidity-free air, so the rhodie’s hanging on to whatever water it’s got by curling up.
The reality. Nope. For two simple reasons. 1) Plants, and that includes rhododendrons, have got microscopic structures – pores – on the undersides of their leaves called stomata.²⁴⁻²⁶ These pores are integral to the process of transpiration, during which carbon dioxide enters the plant through the stomata, and oxygen and water exit through the stomata.²³ But in the case of cold tolerant plants, the stomata remain closed throughout the winter.²⁷ Rhododendron plants are definitely cold tolerant plants. And rhodies’ stomatas are definitely completely closed for business during the cold days of winter.⁸⁻⁹, ¹³ Rhodies don’t curl their leaves in winter to save water because their stomata are closed and they’re not losing any water in the first place. End of story. 2) Rhododendron leaves possess a thick, waxy cuticle, which is a protective layer that allows light to enter the leaf but prevents water loss by evaporation.⁹, ²³, ²⁸ Guess what? That cuticle remains in place during the cold dry months of winter. Definitely no water loss there, either.
So, big picture: the rhodie’s stomata are closed, its cuticle is in place, and no water escapes its leaves during the winter for these reasons, and for these reasons alone. Rhodies are not curling their leaves to save water. End of story.
Misconception number 3: Rhododendron leaves curl in winter to minimize sunlight exposure.
The illusion. The theory here suggests that by curling their leaves during winter dormancy (which effectively starts when temperatures hit the freezing point at 32° Fahrenheit), rhodendrons are minimizing their damage from sunlight energy, which they can neither metabolize nor dissipate due to their dormant states.
The reality. Nope again. Although, as you’ll remember from Section 3 above, rhodies actually do droop their leaves to a vertical position during winter dormancy to avoid damage from sunlight, they don’t curl them to avoid sunlight damage while they’re dormant during the winter. Here’s why: First, when rhodies curl their leaves, it’s their undersides that are curling inward around themselves. The tops of the leaves remain on the outside of the curl, and it’s the tops of the leaves that are primarily responsible for allowing light to reach the chloroplasts (where, again, it’s converted to energy but neither metabolized nor dissipated during the rhodie’s winter dormancy).¹⁴, ²⁸ Since it’s each leaf’s underside that’s doing the inward curling, and the leaf’s top is remaining comparatively exposed to the sun, rhododendron leaf-curling does very little to stop sunlight from reaching the chloroplasts contained in each leaf.⁹ Second, as also noted above in Section 3, the lower the temperatures are outdoors, the tighter rhododendrons curl their leaves. By the time temperatures drop to 20° Fahrenheit and below, a rhodie’s leaves are curled as tightly as they can possibly be. There’s no disputing this. The science backs it up, and I’ve observed it time and time again in my garden. But what I haven’t seen in my garden, and what I don’t need science to back up for me, is a case of a rhododendron plant curling its leaves more tightly in winter due to the presence of bright sunlight. And that’s because it just don’t happen that way. On a sunny 30° Fahrenheit day in winter, those leaves are not curled any more tightly than they are on an overcast and cloudy 30° Fahrenheit day in winter. No way, baby. It ain’t the sunlight on a cold winter’s day that’s making ’em curl, it’s the cold on a cold winter’s day that’s doing the trick. Plain and simple, easy peasy.
Product Recs: Some Old RGG Standbys to Use in Spring, Summer, and Fall to Guarantee Healthy Rhododendron Leaves in Winter
I really do take a ton of pride in my garden’s rhododendron, azalea, and pieris populations, so you’ll forgive me if I feel that showcasing my rhodies in their current shrunken, shriveled condition requires some overcompensation on my part. Here’s a link to my 2022 article here in The RGG, titled “How to Fix Yellow Rhododendrons (and Azaleas and Pieris, Too.” There are some great shots of rhodies, azaleas, and pieris bushes looking good and feeling fine in the spring and summer, and there’s also a great methodology – including a feeding and care regimen, plus products to help implement it and keep it going – in this article. The same products recommended there are also included right here for your convenience. Keeping your rhodies and company healthy and happy during the growing season means keeping them healthy and happy during the coldest months of the year. Use these products in spring and summer, and you can be sure that those rhododendron leaves in winter, even if they don’t look it, will be healthy as hell.
Luster Leaf Rapitest 4-way Soil Analyzer. I bought this Luster Leaf Rapitest 4-way soil analysis meter in February of 2022 and have used it successfully time and time again since then to test for soil fertility and pH levels. It also measures sunlight and soil moisture levels. It’s fast, easy to use, convenient, and accurate. By using this device, I’ve been able to determine the necessity of appropriate fertilizer applications and pH amending to the soil of a large number of the plants in my garden. Order it here, directly from Amazon, by clicking the #advertisement link. Note that this unit doesn’t test for iron levels in soil. Also note that I really love this little meter!
Espoma Organic Soil Acidifier. Whether we’re talking rhododendron leaves in winter, spring, summer, or fall, we know that they’ll be happy and healthy if the rhodies they’re attached to are growing in acidic soil. Espoma Organic Soil Acidifier is the perfect product for lowering the pH and increasing the acidity of your garden’s soil. It’s a fabulous organic product which I use to lower soil pH for plants like my blue hydrangeas and my rhododendrons, azalea, and pieris. It’s very effective and allows acid-loving plants like these to properly access and utilize nutrients from fertilizing products. Order it here, from Amazon, by clicking the #advertisement link.
Espoma Organic Holly-tone. Espoma Organic Holly-tone is an unparalleled food for acid-loving plants and evergreens. It’s an organic formulation with an N-P-K of 4-3-4, a multitude of beneficial microbes, and a respectable amount of sulfur (5%, in elemental sulfur form) on tap for performing its own bit of soil acidifying. As a stand-alone product, there is, in my own experience, simply not a better fertilizer for rhododendrons, azaleas, pieris, hollies, and other acid-loving evergreen bushes. Click the #advertisement link to learn more, or to order it here, directly from Amazon.
Ohrstrom’s Maxicrop Liquid Seaweed Plus Iron. Ohrstrom’s Maxicrop Liquid Seaweed Plus Iron is a remarkable source of iron for acid-loving plants. When used in conjunction with Espoma Organic Soil Acidifier and Espoma Organic Holly-tone, it literally works miracles. It’s got an N-P-K of 0-0-1 and it contains 2% iron. It’s sourced from Ascophyllum nodosum seaweed harvested from the waters along Norway’s coastline. The beneficial effects of this product are noticeable almost immediately after its application. Trust me, your rhododendron leaves in winter will thank you for the Maxicrop treatment you give them in spring and summer. Click the #advertisement link to learn more, or to order it here, from Amazon.
Bibliography/For Further Reading
Below is today’s bibliography/”For Further Reading” list. It’s a list of the cited works that assisted me in writing this article, and that’s helped me with my original and ongoing research into rhododendron leaves in winter and why they do what they do. As always, each entry is listed in link form, so you can click on any one of them to give it a read if the spirit moves you.
- “Ericaceae.” Wikipedia, pp. 1-7.
- “Thermonasty.” Wikipedia, pp. 1-2.
- Melissa Reckner. “Rhododendrons as Thermometers.” Brandywine Conservancy Blog, January 22, 2021, pp. 1-7.
- “thermonasty.” Merriam-Webster, p. 1-2.
- “International scientific vocabulary.” Wikipedia, pp. 1-6.
- “Tropism.” Wikipedia, pp. 1-3.
- “Cold and Curl.” Kruckeberg Botanical Gardens Blog, January 28, 2013, pp. 1-2.
- Elaine Fogerty.”Ask Elaine: Rhododendrons and Winter.” Friends of Lakewood Arboretum Blog, January 28, 2018, pp. 1-3.
- Matt Candeias. “Why Do Rhodendron Leaves Droop and Curl in the Winter?” Piedmont Master Gardeners Association Blog, February 2021 – Vol. 7, No. 2, pp. 1-5.
- Steve Henning. “Caring for Rhododendrons in Winter.” The American Rhododendron Society’s Rhododendron & Azalea News, pp. 1-7.
- Cathy Ludden. “How Cold Is It Outside?” nature Center at Greenburgh’s Around the Grounds, Native Plants, January 20, 2022, pp.1-10.
- Dave Anderson, Chris Martin, and jessica Hunt. “Something Wild: How cold is it? Check the rhododendron!” Society for the Protection of New Hampshire Forests’ Something Wild, February 28, 2024, pp. 1-5.
- Teo Spengler. “How Curling Leaves On Rhododendrons Act Like A Thermometer.” Gardening Know How, May 4, 2023, p. 4.
- “Chloroplast.” Wikipedia, pp. 1-48.
- “Photosystem.” Wikipedia, pp. 1-5.
- “Photosystem II.” Wikipedia, pp. 1-8.
- Nilsen, E.T. Seasonal and diurnal leaf movements of Rhododendron maximum L. in contrasting irradiance environments. Oecologia 65, 296–302 (1985). https://doi.org/10.1007/BF00379233
- Vyse, K., Penzlin, J., Sergeant, K. et al. Repair of sub-lethal freezing damage in leaves of Arabidopsis thaliana. BMC Plant Biol 20, 35 (2020). https://doi.org/10.1186/s12870-020-2247-3
- Kane CN, McAdam SAM. Spatial and Temporal Freezing Dynamics of Leaves Revealed by Time-Lapse Imaging. Plant Cell Environ. 2025 Jan;48(1):164-175. doi: 10.1111/pce.15118. Epub 2024 Sep 10. PMID: 39253967; PMCID: PMC11615429.
- “Flash freezing.” Wikipedia, pp. 1- 5.
- Christine Thompson. “Rhododendron leaves in winter: A moving tale.” Royal Botanical Garden Edinburgh’s Botanics Stories, March 20, 2018, pp. 4-5.
- Wang H, Nilsen ET, Upmanyu M. Mechanical basis for thermonastic movements of cold-hardy Rhododendron leaves. J R Soc Interface. 2020 Mar;17(164):20190751. doi: 10.1098/rsif.2019.0751. Epub 2020 Mar 11. PMID: 32156184; PMCID: PMC7115238.
- “Transpiration.” Wikipedia, pp. 1-7.
- “Stoma.” Wikipedia, pp. 1-12.
- James Urton. “Stomata – the plant pores that give us life – arise thanks to a gene called MUTE, scientists report.” University of Washington UW News, May 7, 2018, pp. 1- 3.
- “Evaporation and Transpiration Basic Concepts.” HEC-HMS Technical Reference Manual, pp. 1-5.
- Wilkinson S, Clephan AL, Davies WJ. Rapid low temperature-induced stomatal closure occurs in cold-tolerant Commelina communis leaves but not in cold-sensitive tobacco leaves, via a mechanism that involves apoplastic calcium but not abscisic acid. Plant Physiol. 2001 Aug;126(4):1566-78. doi: 10.1104/pp.126.4.1566. PMID: 11500555; PMCID: PMC117156.
- “Photosynthesis and plants (CCEA).” BBC Bitesize, pp. 1- 4.
A Short RGG YouTube Channel Video Explaining the Thermonastic Action of Rhododendron Leaves in Winter
The vid is a comparatively brief recap of this article. Click the image link below to watch it.
And, That’s All for Rhododendron Leaves in Winter…
… because spring will be here before you know it!
I hope you enjoyed the article (though “enjoy” might be too strong a word – this was a long one). I appreciate your sticking it out to the end. And, since you’ve made it this far, you’ve now got the goods on rhodendron thermonastic leaf-droop and leaf-curl. You know why it happens, and you know why it doesn’t. You’ve got some great products to use on your own rhodies during warmer days, you’ve got a boatload of additional, informative reading to do if you’re interested, and you’ve got a pretty short synopsis of this article in the form of yet another poorly produced (but admittedly helpful) RGG YouTube Channel video.
And most importantly, you know that the two thermonastic activities in which rhododendron leaves in winter engage – leaf-droop and leaf-curl – are the perfectly normal way that these plants protect themselves in winter.
So, when your rhodies start looking and behaving like certain parts of a dude’s anatomy during a dip in Lake Michigan in the middle of January, you ain’t gotta panic. It’s the dude in the Lake who’s got the sackful of worries.
I think that covers it, gang. As always, I thank you for your continued kind interest and readership.
Cheers, and Happy Gardening!
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Very informative and interesting article….
Always learning something new …
Can’t wait to see all those blooming
flowers in the spring 🌸🙏
Thank you for reading it and for commenting, Roxxy. I really appreciate it. I’m glad you found the article interesting. I really think the whole process of rhododendron cold defense is super-interesting, too. When they look miserable, shriveled, and droopy on the outside, it means that they’re actually really happy and healthy on the inside – they’re getting themselves through the winter so they can dazzle and impress in the spring and summer! Pretty amazing, I think. Thanks once again, Roxxy!
This is a very informative article. My rhododendron looks exactly like yours do. I would always wonder if it would come back in spring. Now I know why it looks this way, and I know not to worry about it! Thanks for the explanation.
Thanks for reading the article, Kevin, and thanks for commenting here. I know exactly what you mean with regards to the “wondering if they’ll bounce back” thing. Back when my rhododendron bushes and I spent our first winter together, I was really alarmed by their shriveled and sagging appearance. Scared the hell out of me. When I see it happening now, I take it as a sign of their good health, because I know they’re doing exactly what they need to do to get through the winter. Sad-looking rhodies are happy on the inside! Thanks once again, Kevin.
Thermonastic droop and curl! I’ve learned something new here! We have rhododendrons here by the ocean, but our temperatures don’t drop as drastically so I don’t think we see that phenomenon as often.
I’m not surprised, Lisa. Air temperatures need to get pretty low for those kinds of leaf movements. When it gets down to the mid-twenties and lower out here, my poor rhododendrons look pretty pathetic with their leaves pointing downward and all curled up like little cigars. If I didn’t know better, I’d be really worried! But it’s just their way of coping with the cold. Admittedly, I do wonder if mine would be happier on the West Coast! Thanks for giving this one a read, Lisa, and thanks for commenting here.
Thank you for this amazingly detailed analysis of Rhoddys – which is our state flower.
We have one – given to us by a friend a few years ago. I like that it has stayed small. I also like that I gets several colours on it at the same time – ranging from lavender to pink to white.
Thank you for reading the article, Annie, and thank you for your kind words. I’m glad you enjoyed it. Your own rhododendron sounds like it really puts on a floral display – those multiple colors sound amazing! When it blooms, you’ll have to send in some pics – I’d love to see them, and I’m sure RGG readers would love to see them, too. Long live your colorful little rhododendron! Thanks once again, Annie.
Enjoyable and informative article and video. Fully explained in an erudite and pithy manner. Thanks again for another special article.
Thank you, Rick. Wow, I really appreciate those kind words. And, of course, I’m very glad to hear that you enjoyed the article. I think the subject is really interesting, and I remember the first time I ever saw my own rhododendrons react this way in the cold. It sparked my interest, resulted in lots of research, and ultimately led to my writing this article. Cool bushes. Literally. Thanks again, Rick.