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WHAT IS HEAT
BY
Most of us are
very familiar with the USDA Hardiness Zones.
In 1997, The
American Horticultural Society (AHS) released
the
Plant Heat
This past
summer and fall the prolonged heat and drought has gardeners very
interested in plants that grow and bloom under these conditions. Many
gardeners are rethinking what they will plant this summer and what
microclimates exist in their garden. They are looking for guidance.
Our youngest
son lives in
However,
The effects of
heat damage are more subtle than those of extreme cold, which will kill
a plant instantly. According to a release by AHS, “Heat damage can first
appear in many parts of the plant: Flower buds may wither, leaves may
droop or become more attractive to insects, chlorophyll may disappear so
that leaves appear white or brown, or roots may cease growing.
Plant death from heat is slow and lingering.
The plant may survive in a stunted or chlorotic state for several
years. When desiccation
reaches a high enough level, the enzymes that control growth are
deactivated and the plant dies.” (1)
The process of
cataloging plants based on a Heat Zone designation is just beginning.
Approximately 500 were initially categorized by the AHS and some
additional ones have recently been completed.
It will take a number of years before all of the plants that have
a Hardiness Zone rating will have a corresponding Heat Zone equivalent.
The Heat
Hardiness Zone map is a start to educate people about the effect of
prolonged heat on a plant.
The one problem is that the Heat Zone map does not integrate data for
humidity, or the variance between day and night temperatures. Just as
with the Cold Hardiness map, temperatures are only one factor that
affects plant hardiness. In
areas with lots of snow cover, plants may survive deadly winter
temperatures because snow, that is at least 4 inches deep, has an
insulating effect on plants and animals.
To better
understand gardening in the heat, I highly recommend “Flower Gardening
in the Hot Midwest”. This book is written by a References:
(1) “A New
Landscape Concept-Heat Zone Gardening” by
(2) “Heat-Zone
Gardening”, Time Life Books, 1998 (This book contains pictures and
descriptions of the first 500 plants categorized by Heat Zone.
It talks about the other considerations that affect plants such
as “microclimates”, “sun and shade”, and “the fine art of watering”, and
has a colored “Heat Zone Map”. It is out of print but may be ordered
from used books stores. Also visit the American Horticultural Society’s
website at www.ahs.org. Copyright 2012 |