Unfortunately, it is not that simple. For
one thing, the official temperature is recorded at one
specific location and is normally taken from a thermometer
several feet off the ground. If your landscape is in a "low"
area at the bottom of a hill, the temperature may have been
several degrees lower. If you are on the top of the hill, odds
are better that the temperature did not go below -20.
Plants in an open, windswept site may suffer
more damage. Cold, dry winds will cause desiccation (drying
out) of the plant tissue. This can make buds and twigs more
susceptible to low temperature damage.
The overall health of the plant going into
the winter will also be a factor. If the plant was
under-watered or undernourished or suffered
site stresses last summer, it is more likely to be damaged by
Many of us "stretch the zone" and use plants
that are really suited to Zone 6 which does not get as cold.
These plants may work out fine for many years until a deep
freeze hits as it did this winter.
Different tissues on a plant respond
differently to extreme cold. Generally, flower buds are least
that set their buds during the
previous fall may not be very showy this spring. Vegetative
buds which will become leaves are hardier than flower buds.
Twigs are hardier than buds and major branches and the trunk
are the hardiest of the above ground parts of the plant.
Marginally hardy species such as peach trees
located on low sites may experience loss of major branches or
the entire plant. Hardy native trees or shrubs may only suffer
loss of a few flowers.
What can you do? For existing plants, the
answer is, "Nothing." Plants that were not hardy enough for
the temperatures have experienced the damage and there is no
going back. Inspect the new growth in the spring and remove
the dead tissue.
For the future, use plants known to be hardy
for Zone 5 or lower. Keep plants as healthy and stress free as
possible during the growing season but do not stimulate lush
new growth in the fall. Plant marginal species on high sites
and/or protect them from raw winter winds.