Actively growing plant tissues, such as leaves, need water to carry on their metabolic business. In the winter, plants are subject to the harsh environment of freezing temperatures and cold, dry winds. Leaf and bud cells, bloated with water, would explode if they froze, because frozen water takes up more room than liquid water. How do plants respond?
Millions of years ago, before the Ice Ages, the earth’s climate was pretty much the same everywhere most of the time. Even in Delaware County, what wasn’t covered by sea water was forested with tree ferns, cycads and plants that we think of now as tropical plants. As the earth’s climate destabilized, the Ice Ages occurred and seasons developed. Plants evolved with different strategies to survive winter.
Most of the plants which survive today in Delaware County are deciduous (they respond to winter by dropping their leaves and going into dormancy). Some plants have evolved other responses. In a previous post, I discussed plant antifreeze as one response to extreme winter conditions.
Rhododendrons don’t go completely dormant during the winter; they keep their leaves through the winter and have a different strategy to survive. When the temperature drops to below 20 degrees, Rhodie leaves move so as to expose less surface area to drying winds and thus conserve water. When the temperature rises to above 20 degrees, the leaves resume their normal position.
The same plant one day later and 10 degrees warmer…