If you see curled up leaves in the summer, though, that is a sign that your Rhododendron is much too dry. Until then, I think its safe to say that we can appreciate and, to some degree, rely on the spot forecasting abilities of these wonderful shrubs. Researchers found that Rhododendron leaves freeze completely at temperatures below -8 degrees Celsius (17.6 degrees Fahrenheit), temperatures that occur regularly throughout the range of temperate Rhodo species. Water immediately! In the spring we all play a waiting game. If heavy snows break branches, so that they can no longer take water up to the leaves, this too causes foliage to curl and die. This seems pretty far fetched for a few reasons. Throughout the growing season, they are generally shaded by the overstory. For starters, Rhododendron simply do not open their stomata during the colder months. However, once the canopy leaves fall, things change. Rhododendrons Curl Their Leaves Against Winter Wind. If the leaves were to remain horizontal, this could cause enough snow buildup to break branches. When living tissues freeze, ice crystals build up to the point that they can rupture cell membranes. So, why do the leaves curl? These experiments also revealed something else about the changes in leaf position when it comes to shape. Sometimes one or more of these are contributing factors because if the rhodys went into the winter season dry from summer drought they are then more likely to be further stressed by cold winters. As it turns out, curling made no difference in protecting the leaves from light damage. Many a Rhodo lover has said that they can tell how cold it is outside by looking at Rhododendron leaves. Also, their thick, waxy cuticle keeps water within the leaves from evaporating out as well. Leaf curl on Rhododendrons is most frequently seen when the plants are under stress from drought, stem injury or cold temperatures. The fact that a considerable amount of ice and snow can accumulate on branches regardless of leaf position, and largely without harm, seems to suggest that this is not the case. Some Rhododendrons drop those curled and soon to be dead leaves but will put out new foliage from those stems in late May. By keeping them closed, there is no net transfer of water into or out of the leaves. Many a Rhodo lover has said that they can tell how cold it is outside by looking at Rhododendron leaves. 2. Experiments have shown that leaves that were forced to stay horizontal during the winter experienced permanent sun damage and photosynthesized considerably less than leaves that were allowed to droop once favorable temperatures returned. Wait and see how the plant recovers in late-May. Though we generally don't think about photosynthesis in the winter months, evergreen plants actually experience the highest light intensities of the year during this time period. Why does this happen? The leaf gall fungus, Exobasidium vaccinii, distorts the shape of rhododendron leaves so that they curl backward rather than downward, as in the case of curling caused by weather. These leaf movements do seem to be tied to the weather but their triggers and function have been the source of a lot of debate. You can take one of two actions: 1. The first of these has to do with the sensitive photosynthetic machinery inside the chloroplasts. Again, experiments were able to demonstrate that flat leaves thaw much more rapidly than curled leaves. Why Do Rhododendron Leaves Droop and Curl in the Winter? Finally, leaf drooping and curling happens long before the ground freezes and therefore doesn't seem to be triggered by a lack of water in the environment. To best preserve tissues via freezing, they must freeze quickly, which reduces the size of the ice crystals that can form, and then thaw out slowly. Download Garden Answers Plant Identifier App Today! of rhododendron leaves began in 1899 with the work of Harshberger. Certainly not all Rhododendrons are cold hardy but those that are seem to benefit from reorienting their leaves. Other plants will continue to die back and you’ll see in early June that these branches are indeed dead, at which point you can cut them off. What’s to be done now? Once a section becomes afflicted the progress of the affliction spreads rapidly. The plant is about 7 feet tall and 6 feet in diameter. Copyright © 2020 Garden Answers | All Rights Reserved |. Title: Why do Rhododendron Leaves Curl? This will prompt new growth from the area where you’ve left two leaves. The leading theories on this phenomenon seem to deal more with issues at the cellular level. How Overharvesting is Changing an Alpine Plant in China, Why Plant Relationships Matter for Caterpillars, The Knife-Edge Economy of Panama's Trash-Basket Treelet. Fertilizer won’t fix the problem so don’t go there. It would seem that drooping and curling are responses to two different types of environmental stress. This is because a curled leaf exposes far less surface area to the warming sun than does a flat leaf. These leaf movements do seem to be tied to the weather but their triggers and function have been the source of a lot of debate. In 1933, a Japanese scientist, Y. Fukuda, studied the leaf-curling patterns of Rhododendron micranthum, mak-ing the important observation that its leaves could be kept from curling if he covered them with snow, thereby insulating them from cold air temperatures. Broad leaved, evergreen plants living in the temperate regions of the world face quite a challenge come winter time. This is only exacerbated if the tissues thaw out quickly. What to Do with Rhododendron with Scorched Leaves Damaged leaves and branches may or may not recover. As the leaves droop and curl, they are hypothetically increasing the humidity around their leaves and thus reducing their chances of desiccation. Anyone that has ever tried to freeze and then thaw leafy vegetables knows what I am talking about. It seems to be happening in sections of the plant. Winter Burn Although rhododendron leaves tend to curl during cold weather, it may not always protect them from winter burn. Sometimes one or more of these are contributing factors because if the rhodys went into the winter season dry from summer drought they are then more likely to be further stressed by cold winters. Freezing temperatures, lack of water, and often intense sun can exact quite a toll on living tissues. The thought is that by positioning the leaves vertically, the plants are reducing the amount of direct light hitting them throughout winter and therefore reducing the potential for light damage.