I got an email from Rossana today:
When your country doesn't have a hardiness map, or the planting maps for your country are more than twenty years out of date (Mexico's haven't been updated since the 1980's), the first thing to do is to find the minimum average temperature for your area, as well as your record low temperature.
Both these numbers should cover as many years as possible, as recently as possible. Information over 20 years old is probably no good and more recent data should be obtained.
You can find this information in several ways:
Once you have your minimum average temperature, you should compare this to a hardiness zone chart.
Since most plant hardiness zone maps are taken from the USDA planting zone map, and this is the most commonly used reference for online plant information, I'll use that here, but you can refer to any hardiness chart that makes sense to you.
If you hold a ruler or a piece of paper at your minimum average temperature, you can then go across and see where your USDA zone is.
According to the Wikipedia page, Campeche's average low is 70.3F/21C, which puts Rossana in zone 13, much different than it was in 1984!
(for those of you wondering, zone 13 is anything with an average minimum temperature above 60F/15C -- there is no zone 14 ... yet)
The reason I had you find your record low temperature is that you should be aware of what zone that is too.
For example, the record low for Campeche is 36.5F/2.5C, so if Rossana buys plants that are hardy in zones 10-13, she can be confident that there won't be any problems with them in the near future as far as cold damage (which is what a hardiness planting zone map is about).
Now, you should be also aware of the other types of planting zones (for example, Campeche has a tropical climate, so many desert plants may not do well there), but knowing your plant hardiness zone is a great way to begin.
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