Garden in winter

Why Don't Plants Freeze In Winter?

Excerpted from: Beautify

The mercury has plunged to a record low, winds are howling and the wind chill is off the charts. Sound familiar?

The radio warns us that exposed flesh can freeze in mere minutes. Brrrrrr, we think, as we bundle ourselves up just to walk the short distance to the car. A Wisconsin blizzard is on its way.

But spare a thought for the poor plants in our gardens. What about that yew under the front window with the icicles hanging from its needled branches? The evergreen rhododendron with its leaves curled into tight little rolls? The magnolia with its furry, brown buds? How do they protect themselves from the extremes of winter weather?

Plants are built of cells and viscous fluids just as animals are, they are at a great disability when it comes to seasonal environmental stress. Animals can remove themselves from harm’s way, but plants are stationary.

Although plants are built of cells and viscous fluids just as animals are, they are at a great disability when it comes to seasonal environmental stress. A man, a marmot or a moth can remove themselves from harm’s way, but plants are stationary. The yew needles must submit to sheets of freezing rain. The magnolia buds must hold tight against a blizzard. The rhododendron leaves must brave Arctic winds.

  Plant Adaptations

Yet nature has armed plants with remarkable defense mechanisms to help them withstand the stresses of both heat and cold.

These adaptations help trees and shrubs withstand the worst extremes of winter weather. But they’re no guarantee against that once-in-century ice storm that tears jagged branches from sturdy trunks; the atypical January cold front that sets record lows while confounding a tree’s genetic definition of normal; or that sudden spring freeze that pierces newly-awakened cellular protoplasm with lethal ice crystals.

They are merely the best that nature can do.


Cold Acclimation

Frost on plant Most important is a plant’s inherited genetic adaptability to seasonal change. In woody plants that must survive winter, this is called cold acclimation.

Plants must possess the genetic makeup to develop tolerance to harsh winter conditions. Low temperature induces the expression of many genes in plants.

Plants vary in their degree of adaptability, of course, depending on their locality or ecoregion. A rhododendron native to the subarctic tundra (Zone 1) such as Lapland rosebay, Rhododendron lapponicum, will survive far lower winter temperatures than the American rosebay rhododendron, Rhododendron maximum native to the cool, moist Appalachian Mountains (Zone 4). To that end, the Lapland rhododendron will maintain a compact height (rarely over 30 cm or 1 foot), thus exposing a minimum of its above-ground growth to the elements, whereas the southern species can afford to grow to an extravagant 7 meters (20 feet).


Woody plants may also employ two metabolic genetic strategies to help them deal with freezing temperatures. The first strategy is avoidance, for instance, the prevention of the formation of ice crystals in cells through the encoding of genes for super-cooling proteins that protect intracellular tissues.

  Freeze Tolerance

The second strategy is freeze tolerance. Plants that must survive even lower temperatures, like the Lapland rhododendron, contain genes that encode cold-stress-responsive proteins. These proteins cause the plant to evacuate water from cellular protoplasm into intracellular spaces where ice crystals can form without damaging the plant.

Provided these adaptations occur in a timely fashion after the plant has acclimated in fall, provided winter temperatures do not exceed the plant’s maximum low temperatures, and provided the plant is not lured out of dormancy by prematurely warm spring temperatures that plunge again later, there should be no tissue damage to the plant.

  Thermonasty: movements in response to a temperature change

Thermonasty Leaf Curling

Thermonasty is a non-directional response in plants to temperature. It is a form of nastic movement, not to be confused with thermotropism, which is a directional response in plants to temperature.

These movements are plant movements triggered by an external factor such as cold, heat, light or humidity. Unlike the nerve-generated movements of animals, plants “move” through changes in the internal cellular pressure of their parts. In extreme cold, the leaves of many evergreen rhododendrons exhibit thermo-nastic movement, curling the upper surface of the leaf inwards and pointing it down toward the ground, thus minimizing exposure to freezing temperatures and also reducing winter-burn caused by winter sunshine.

  Leaf Size and Composition

Reduction of leaf size is an important adaptation of conifers, many of which are indigenous to the northern boreal forest zone where cold, dry winters are a fact of life. Trees must invest abundant energy to produce their leaves, but the lean, nutrient-poor soil, the harsh atmospheric conditions and the short growing season of the northern forest do not favor an annual leaf cycle, as with deciduous trees. Therefore, depending on the species, conifers retain their oldest leaves for 2 years (white pine) to 45 years (Great Basin bristlecone pine) – that is, they stay “evergreen."

While a full leaf canopy allows a tree to begin photosynthesizing early in spring and stay photosynthetically active later in autumn, it also invites desiccation and freeze damage in winter. Thus, conifers have adapted by producing small, narrow, needle-like leaves (spruces, pines, firs, hemlocks, yews) or scaled leaves (cedar, cypress), reducing the surface area to reduce transpiration of water and the risk of freezing. They also have fewer stomata (pores) in the needles than deciduous leaves.

Evergreen conifers and broad-leafed evergreens also protect their leaves from desiccation in winter by covering them with a new layer of cuticular wax each summer.

  Winter Buds

Frozen tree bud Those furry winter buds on the magnolia and the shiny, dark-brown ones on the horse chestnut are more than mere cold season finery. Their overlapping scales form a watertight, protective covering for the embryonic leaf and flower shoots that will emerge in spring. The buds of conifers are covered with protective wax or pitch, giving them extra insulation against winter weather.

Further Information

 Soil In Winter
 Getting Started: How To Use Cold Frames
 Do Plants Breathe?
 Can Plants Tell Time?

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