Why Rhododendron Leaves Roll Up in Cold WeatherDecember 16, 2008
As temperatures have plunged into the 20s (or lower) and we’ve bundled up and watched the snow fall from our heated indoor perches, garden plants are left to fend for themselves day and night under blankets of ice and snow and amid desiccating winter winds. As the soil begins to freeze up and water uptake becomes more difficult for roots and as the dry, cold air above ground begins to sap moisture from plants, rhodies and many other plants take precautions to conserve their moisture.
Briefly, plants take up moisture in root systems and transport the water upward through roots, trunks, branches, stems and leaves. And, through the underside of leaves, water is released through leaf stomata. As water is released through the stomata, more water is drawn upward toward that same stomata. (The entire process is more complicated than that, but you get the basic idea, right?)
When a plant is faced with environmental stresses that may cause it to release more water than it can take up, which would lead to dieback in the plant, the plant will close its stomata and essentially “shut down the factory” living on reserves until the weather either warms (or cools) to a friendly temperature. Then, the leaves unroll (or in hot weather they may “unwilt”), the stomata open and the factory process of transporting water and photosynthesizing resumes.
So, don’t worry about those curled up, frozen-looking rhodie leaves. They should be just fine. You may see some frost burn later, but odds are the plant is doing what it needs to do to take care of itself while the weather outside is frightful. By spring, new leaves and beautiful blooms will unfurl.
(Oh, and in case the teaser on hot weather and wilted leaves left you wondering…a plant that will commonly “wilt” its own leaves on a hot days, despite sufficient soil moisture is the lovely hydrangea. As soon as the sun sets and the temperatures cool down, they perk right up again. Ah, to have a hot sunny day right now, right?)
Have any other garden concerns during this cold season? Please write in, and we’ll do our best to help you help your garden during this unusual Pacific Northwest cold snap.