Freezing Temperatures Affect Plants
Plants Freeze . . .
Ice, and Plants, 101
Not all plants react the same way to freezing temperatures. Native plants and
others that originated in cold climates have adaptations to survive typical
winter conditions. Plants that originated in more tropical locations have fewer
defenses against freezing temperatures.
Plant leaves contain many layers of cells. Water inside the leaves, but outside the
cell walls, is relatively pure, so it freezes at 32 degrees F. But water inside the
living cells of many "hardy" plants has dissolved salts, sugars, and
other substances that act like anti-freeze. (They lower the temperature at which
the water freezes.) So water in the living parts of cells in winter-hardy plant
leaves has some protection against freezing. But it will freeze if temperatures
drop suddenly or extremely.
freezes, it expands; this can rupture cell walls and other parts. Frozen
water between cells can also draw water out of the cells, causing them
to shrink and rupture. The ice crystals that form between or within
the cells exact the most damage; these can act like miniature needles,
piercing cell walls and the living parts inside.
of thawing out can be more dangerous than freezing! Water can flow
back to a damaged cell and cause it to burst. Students may see evidence
of this when they observe leaves after taking them out of the freezer
and again once they thaw.
If a plant
is to survive freezing winter weather, it needs to protect cells from
ice crystals, or prevent crystals from growing big. Here are a few cool
plant adaptations for getting by:
If you have a spring snow or freeze, what will happen
to your tulips? The plants should be fine at 20 or 25 degrees.
But below that, any frozen part will turn white and not be able
to make food to form a flower or to store for next year's bulb.
If a tender flower bud freezes, it will not likely bloom.
- Seeds: Plants
that have only an annual cycle get through the winter by making
dry seeds; can survive freezing.
- Toughening/"Anti-freeze": Some
plants toughen up or "harden" in the fall in response
to slowly increasing temperatures. Most produce sugars and salts
that prevent ice crystals from forming or growing large. They also
gradually lose water; the drier tissues are less likely to freeze.
Loss/Adaptations: Some plants simply lose their leaves
altogether and store energy in their roots. Others, such as spruce
trees, have needle-like leaves with waxy coatings; these prevent
water loss and cold damage.
Water Location: Some plants keep water in cell walls,
but keep it out of the living part of the cell where ice could
kill the plant.
Storage: Some plants, like tulip bulbs,
store energy in underground structures. Temperatures at that
depth rarely fall much below 30 degrees F. Sugars in a hardy
bulb, like salt on a winter sidewalk, lower the temperature at
which water freezes.
the Strategies Might Fail
Even a hardy plant can suffer or die under certain winter
conditions. These include the following:
temperatures fall below a plant's maximum low-temperature limit
even after it has acclimated (toughened up!)
early freezes occur before the plant has acclimated in the fall
unusually late freezes occur in the spring after the plant has