[NAFEX] tropical, subtropical definitions

M Stanton 6ducks at comcast.net
Tue Feb 27 09:16:37 EST 2007

Tropical?  Subtropical?  Let’s define some terms!  


Truly tropical plants cannot handle temperatures below 50 °F without damage,
and are from areas where the monthly mean temperature (every month!) is no
lower than 70 °F. Tropical regions are those located at sea level or
low-elevation areas between the Tropic of Cancer and the Tropic of Capricorn
on the map, no further than 23.5 °N latitude, and no further south than 23.5
S latitude. Even at the Equator, however, plants from high-altitude climates
aren’t tropical because they live with cooler temperatures.  In many
tropical places temperatures never dip below even 60 °F.  Tropical plants
may be briefly deciduous, but this deciduous period is not due to cold
weather. A truly tropical plant is the pineapple.  It is not happy below
about 55-60 °F and does best with warm sunny days in the high 70s or 80.
You cannot grow it commercially in the continental US without supplemental
heat.  Tropical plants do not need winter chill. Tropical climates may be
wet or dry.  So pawpaws, some bananas, maypops, many citrus, etc. are not
tropical plants.  


Subtropical (sometimes synonymous with semi-tropical) plants are from areas
of mild climates north or south of 23.5 ° latitude to almost 40° N or S
latitude; if well-acclimated, they can withstand light frost, but not a
severe one.  They can take some chilling but do not require chill hours.
Mango, avocado, many psidium species (guava family), and many citrus plants
are subtropicals, as are some high-elevation plants from otherwise tropical
areas such as the cherimoya, Annona cherimola.  Subtropicals can be grown in
many areas of USDA hardiness zones 8-10.  If you look at the map of the US
you would think that since 40°N latitude runs across a good portion of our
continental land mass, plants such as the pawpaw and maypops are
subtropical, but they are not.  Since they both tolerate very low
temperatures (to 0 °F) and appear to need chilling, (pawpaw requiring
anywhere from 400-1000 hours), they are temperate (cold-winter) plants.
They may have subtropical or tropical ‘cousins’ but they themselves are not.


That brings us to temperate climate plants: plants that tolerate very low
temperatures, sometimes well-below 0 °F, and need a definite period of
chilling.  Apples, peaches, pears are typical examples.  Maypops and pawpaws
(Asimina triloba) also fall in this category.  Furthermore, even if you grow
a low-chill apple in Malaysia or San Diego, it is still a temperate climate


For more information, look up the Koppen climate classification system.


Happy fruit growing!

Michele Stanton


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