The chill of this spring hasn’t been good for many trees.
Several freezes separated by
warm weather have caused major damage.

Your oak may produce no acorns this year because the cold has
killed all the female
flowers.

Trees can adjust to freezes, but these changes depend on the
tree’s health, how much
food it has stored and how fast temperatures change.

For a tree, cold weather survival can be costly and
disruptive, leading to stress and
tissue death.

Many trees can survive extreme cold. A northern willow holds
the record for survival at
minus 320 degrees Fahrenheit in a laboratory.

Trees need time to prepare for freezes. Rapid change from
warm to cold can damage the
most hardy tree.

If given time to adjust, a live oak (Georgia’s state tree)
can survive to minus 18
degrees. Southern magnolia and longleaf pine can survive to
minus 50, sweet gum to minus
20 and American elm to minus 55.

When tree tissues get this cold or colder, they’re severely
damaged. The parts a spring
freeze will damage most are the growing areas at shoot tips and
along twigs.

Flower buds are extremely sensitive to cold. On one tree,
flower buds may be 20 to 30
degrees more sensitive than leaf buds.

Roots are tender, too. They can’t adjust well to freezes once
they’re growing. Cold
damages leaves, if present, along the main veins and connection
to the tree.

The living tissue right behind a bud, connecting it with the
twig, is highly
susceptible, too. It’s small, active, unprotected and
exposed.

The water-carrying tissues, which are dead when functional,
aren’t affected. This leads
to what is called false, or dead, blooming in some trees. The
blooms come out but quickly
wither because connections to the living tree have been
killed.

Trees make a natural antifreeze to survive freezes. They do
this in two stages.

The first requires a gentle cooling-down to below 55 but not
to freezing. The tree
starts to gather sugars and break down stored starches.

As the weather chills over a few days, trees start to change
their living membranes to
maintain a liquid, cold-temperature form.

Trees easily damaged by cold usually can’t modify their
membranes, which become
impermeable solids when cold and suffocate the cells.

Stage two happens below freezing. Trees use collected sugars
and proteins to bind water
inside living cells and prevent ice crystals from forming.

Between the cells, ice can form and pull water from the
cells. If too much ice forms,
new or sensitive tissues are mangled.

Across the range of a tree species are usually many climatic
races. Each has developed
in areas with unique fall and spring temperature patterns.

Moving Southern races farther north can damage trees. A rule-
of-thumb is to beware of
moving native trees more than 100 miles south-to-north or 300
miles east-to-west.

Southern trees moved only a few hundred miles north can have
many problems:

* They don’t develop enough resistance to cold damage.

* They aren’t fast enough in developing resistance in the
fall.

* They come out too early in the spring.

* And they’re killed by extreme freezes that happen every few
years.

Northern tree races won’t grow early enough in spring and
will shut down too early in
fall to stay healthy farther south.

Trees are tuned to their environment. They make all the
materials and growth responses
they need to survive and thrive in normal weather. But extreme
and unseasonal cold can
stress them badly.

Keeping trees healthy is one of the best things you can do to
keep down the stress of
hard freezes.