For:
By: Daniel
E. Mullins
Extension
Horticulture Agent
Protecting Cold Sensitive
Plants
The first hard freeze or killing frost will be
arriving soon and some gardeners are concerned about potential cold
damage. In many cases there is no reason
for concern, but there is one group of plants that could use some help in order
to better survive the winter.
The
tropical and subtropical shrubs on the other hand, are subject to being killed
to the ground or worse, depending upon how low the temperature goes and
associated conditions during a particular freeze. These tender shrubs have become very popular
over the past 10 years and gardeners are establishing them because they are
colorful and thrive during our hot, humid summers.
Hibiscus, Pentas, Allamanda, Cassia, Datura
and Plumbago are examples of such cold sensitive plants. Though they can be seriously winter damaged,
many gardeners feel that the benefits outweigh the risk. Following are some tips for helping these and
other tender shrubs to survive the winter.
■ Thoroughly irrigate 1 or 2 days before a freeze is
expected. Well-watered plants survive
extremely low temperatures better than those that are drought stressed.
■ Covering can provide several degrees of cold protection. However, this method requires a commitment,
so limit its use only to those more valuable tender plants.
Proper covering protects by
trapping ground heat, so in order to work the material must be draped over the
entire plant and in contact with the ground on all sides. The material should be opaque, not
clear. Plastic makes a poor
covering. Use blankets, sheets or
similar materials. It will be necessary
to secure the covering material to the ground by placing bricks, blocks or
other heavy objects.
The covering should be in place
a few hours before a freeze is expected to occur and must be removed when
temperatures rise above freezing.
Coverings left on for too long, being exposed to rising temperatures and
direct sun can result in serious plant damage.
Ironically, many plants have been protected through a cold night, only
to be baked the next day because the covering was not removed promptly.
■ Mounding protects the base of plants against hard freezes. This method is commonly used on citrus and
other cold sensitive grafted plants.
Just before the first freeze
pile sand, shavings, pine needles or similar porous material around the base of
the plant to a height of 12 to 18 inches.
The material can be left in place all winter but must be removed as soon
as the danger of extreme cold has passed in late winter or early spring. Mounding insulates the trunk or stem base and
helps to ensure that at least some live tissue above the graft union will
survive hard freezes.
■ Potted tropicals or subtropicals should be brought indoors for
the winter. Placement in a greenhouse is
ideal, but they can be overwintered in a bright room or even in a garage.