Since they can’t don gloves and a scarf or shiver to keep warm, it’s a wonder that trees, vines and shrubs don’t freeze to death in winter.
Sometimes, of course, they do. But usually that happens to garden and landscape plants pushed to their cold limits, not to naturally cold-hardy plants or plants in their native habitats.
Think about it: Water freezes at 32 degrees Fahrenheit — not a particularly cold temperature for a winter night — and plants contain an abundance of water. Water expands when it freezes, so you can imagine the havoc that would be wreaked if water-filled plant cells froze and burst. But adapted trees, vines and shrubs survive temperatures well below freezing each winter, and those of boreal regions live where temperatures dip below even minus 150 degrees.
Supercool Plants
Water, whether in a plant cell or a glass, does not necessarily freeze as soon as the temperature drops to 32 degrees. To freeze, water molecules need something to group around to form ice crystals, a so-called nucleating agent. Without it, water will “supercool,” remaining liquid down to about minus 40 degrees.
All sorts of things can serve as nucleating agents — bacteria, for instance.
More Ways Plants Deal with Freezing Temperatures
Plants have another trick for dealing with the cold: letting water freeze only outside their cells, where the ice doesn’t do damage. Cell membranes are permeable to water, so as temperatures drop ice crystals that form outside plant cells grow with the water they draw out of the cells. With increasing cold, a plant becomes threatened more by dehydration than by freezing.
