Click here to open USDA Hardiness Zone Map
The production of good quality plants is a major concern of growers. Environmental conditions play an important role in achieving
successful growth and development of any kind of nursery commodity. Among many factors that will determine the growth of the
plants (like soil type, latitude, rainfall, winds, act.), temperature is of the first rank, and has to be taken seriously
under consideration.
Each plant has a range of temperatures, confined by the minimal and maximal thresholds under which plants can perform its vital
functions. Beyond that range, temperatures become lethal and either cold or excess heat is fatal to the plant. It is critical
to meet the optimum temperature requirements of selected plants.
Areas of commercial production are most often limited by:
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Minimum winter temperatures
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Timing of first fall frost
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Timing of last spring frost
The USDA (United States Department of Agriculture) provides a general indicator that is widely used by growers, in the form
of the map and accompanied table. In that system, the US is divided into 11 regions. Divisions are based on average minimum
temperatures during the winter season. The fact that it is the average minimum and not the absolute minimum temperature is
worthy of notice. Data has been collected over many years (since 1974), and the temperature in your zone can get much cooler
than what the table is showing! However, the zone map is a great tool when evaluating the feasibility of a new crop production
enterprise.
A plant’s assigned hardiness zone is the lowest temperature they are expected to survive with any reliability. Zones
are numbered from the harshest (lower #) to the mildest (higher #).
How to use zone map?
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First identify which hardiness zone you live in.
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Use that # as a references when selecting plants from catalogs and nurseries.
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Most varieties will thrive excellently in a wide range of temperatures
There are several other plant hardiness zone maps published, so when comparing a plants ratings versus a zone rating make sure
that they correspond. Occasionally plants assigned to, for example zone 7, can suffer freeze damage in zone 8. Apparently
the hardiness zone system is not totally foolproof. One of its major limitations is lack of information about occurrence of
temperature fluctuations.
A large percentage of losses occur after a warm winter followed by a cold spring spell. Plants loose their hardiness and freeze.
Obviously, zone mapping is a general guideline, and each grower has to acquire the knowledge of their specific microclimate
conditions.
Factors that will change climate are for example:
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Elevation- the higher the area, the colder the winters.
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Hills- south and west slopes are the warmest.
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Body of water- the closer the proximity to a body of water, the milder the temperature.
For annual crops and others that are treated as such in your area, minimum winter temperatures are not a major concern.
It is advisable to analyze your climate for a frost- free growing season. Data can be obtained that will indicate dates of
last occurring frost and the first frost in the fall. The best source of such information is your local Extension Service
Office.
Click here to open USDA Hardiness Zone Map
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