How plants prepare for winter
In all but the warmest regions, most plants go through a period of
dormancy during the winter. Actively growing plants cannot withstand freezing temperatures
for an extended length of time, so plants have adapted by going dormant during the coldest
months. During dormancy, growth stops and the plant remains in a state of rest until good
growing conditions return.
Though August and September can bring some of
the summers warmest weather, by this time most perennial plants have begun
preparations for their annual rest. You might think this hardening off process would be
triggered by cooler weather, but in fact it is the shortening day length that gives plants
the signal. The hardening off process is, at least in part, a photoperiodic response; that
is, it is a response to changes in day length. Many plants, notably the spring-flowering
trees and shrubs, set their flower buds at this time. As the days grow shorter, plants
slow and finally stop any new growth. Then the plant withdraws nourishment from the leaves
and enters a fully dormant phase.
Different types of plant tissues respond differently to
temperature extremes. A peach trees leaves and branches, for instance, may be able
to withstand temperatures of -10ºF. But the flower buds may be damaged at temperatures
below zero. If the buds are damaged, then the next seasons flowers and fruit will be
affected. Peach trees thrive in places like Georgia where minimum winter temperatures
generally dont go below 0ºF. Gardeners living where temperatures frequently go
below zero should look for peach tree varieties that are particularly winter hardy.
Plants that have not finished the hardening-off process
can be damaged by the onset of cold temperatures. Some factors that influence whether or
not damage occurs include: the type of plant and its overall health, what stage it had
reached in the hardening off process, and whether the onset of low temperatures was
gradual or sudden.
What can gardeners do to speedor at least not
hinderthe hardening off process? While cold-hardiness is a genetically determined
trait, it is also influenced by cultural practices. Most winter injury occurs in late fall
and early winter, when a freeze occurs before the hardening off process is complete.
Gardeners should be careful to avoid anything that may slow this process. For example,
fertilizing with a high nitrogen fertilizer after mid-summer can stimulate plants to
continue growing into fall. Sometimes late-summer pruning can also stimulate fall growth.
Heres one trick to help your roses during the hardening off process. Leave the last
flowers to mature on the canes, rather than cutting them or dead-heading the spent blooms.
Let the flowers continue to develop into the "hips," or fruit. The process of
developing fruit and maturing seeds seems to encourage the plant to harden off properly.