HOW TO SELECT A SPECIES

To ensure the survival of your treasured tropical, do not only consider USDA Zone minimum temperatures but rather year round climatic conditions:

Winter Climate and Duration of a Freeze
USDA Zones are based on minimum temperatures. However, these zones contain no information about the length of an average freeze. So, if you select a species based on it's minimum temperature rating you should add some margin - select a hardier species. Especially if your average freeze duration is longer than a few hours or temperatures stay below the freeze point for more than a day after an absolute minimum.

Fall
If your fall temperatures are warm or even hot and generally conducive to plant growth then there is a risk the plant will get shocked by a sudden temperature drop in the winter. Usually a plant in a dormant state has a much better chance of surviving a freeze. So, a a prolonged fall with cold but not freezing temperatures is great.

Spring
The same rule of thumb applies here as for the fall season: Cooler is better! If your spring temperatures jump right away to levels conducive to growth, a belated spring freeze can do tremendous damage to the tender young spring growth.

For example, S.E. Asia experiences moderate temperatures during spring and native plants are used to start growing already at low temperatures. S.E. Asia never experiences late spring freezes because numerous mountains up north protect the area from arctic colds. So, the plants are safe to grow during the spring season.

In the S.E. US, however, spring temperatures heat up fast but because of the lack of northern mountains, there is always the danger of an arctic air mass reaching the Golf of Mexico at this time. Native plants protect themselves by waiting for the real hot summer temperatures before they start growing.

Bottom Line: Make sure if you experience occasional late spring freezes that you select a species that waits for hotter temperatures to grow (i.e. all Sabal species). HIGH RISK SCENARIO: Planting a Livistona chinensis (China) in Dallas, Texas.

Summer
Generally most tropical plants love hot temperatures and even require it for growth and sugar production. So, if summer growth is less than what dies in the winter, your plant will eventually parish even if it survives the cold winter freezes. Also, if low summer temperatures keep a plant from producing enough sugar, the freeze point of it's sap is drastically reduced in the winter. Rule of Thumb: Hotter is better!

Example: A Rhapidophyllum hystrix - one of the hardiest palms in existence (min. temp. wise) - cannot be grown reasonably well in northern Europe because it is just too cold in the summer.

Winter Moisture
Many tropicals need moisture with increased heat and growth; however, during the dormant season these plants are used to dry conditions like in the S.W. US. So, planting such species in areas with a winter rain season (i.e. N. Europe) might prove to be fatal: First, water accumulating in the top of a palm can freeze and physically destroy the growth-center (i.e. Phoenix canariensis). Second, constant ground moisture during the dormant period can decrease a plant's sugar level through osmosis (more water is taken in by the roots than the plant uses). Therefore, the freeze point of the plant is drastically reduced. Also, the root system of such a species will rot much faster (i.e. Butia, Jubaea, Nannorrhops, Trithrinax)

Tips, Tricks & Solutions To Fooling Your Climate
So, now you know you can plant only half of the potentially hardy species in your area just because it is too warm in fall or rains too much in the winter. Find what you can do to grow the other half of the hardy species too: Changing Climatic Conditions.