The plant hardiness zone assignment (for example, on a tag or label) tries to tell you how much cold a plant can withstand.
What kind of hardiness zone map are you looking for?
Hardiness zone maps are extensively used by websites, books, magazines, and other publications to give you some idea of whether a plant can survive the winter in your area. In general, any time you are looking for a plant to buy online, you will be asked for your hardiness zone.
Plant hardiness zone maps began with the USDA plant hardiness zones developed by the US Department of Agriculture. Many other countries use this system as well.
Here are some plant hardiness maps. Although many of them are just the USDA temperature classifications mapped onto other countries, some countries have developed their own maps, and if you live in one of these countries, you should study how the numbering systems differ.
An Australian version of the USDA map -- this one is interesting, because it has an interactive portion that you can change to see average maximum temperature and mean temperatures as well. This would be more useful if the data was taken later than 1990, but it's good information.
This is a relatively new Australian hardiness zone map, developed by the Australian National Botanic Gardens. It's similar to the USDA map but splits the zones differently.
Plant Maps is a site with interactive US, UK, and Canada plant hardiness maps, including one that was updated in 2010. Fun!
A pdf file of the South American USDA plant hardiness zones. I find this difficult to read because the plant hardiness zones are not color-coded, just written on the map. However, this shows topography, cities, and includes zones 12 and 13, which are not seen in North America, so it may be quite useful for you.
There are some drawbacks to simply mapping the USDA plant hardiness zones onto another country (one being the differences in climate caused by the ocean on an island country like the UK, for example), so the Royal Horticultural Society and European Garden Flora have developed their own plant hardiness maps and zoning systems.
Another one of the British Isles and Europe. This one is not interactive, but shows more of eastern Europe, along with Iceland, a bit of northern Africa, and part of the Middle East.
If you're in the former Soviet Union, the Missouri Botanical Society has a detailed discussion (with maps) of plant hardiness zones there and how they compare to the USDA zone map.
Here are two maps for Africa:
The USDA map has historically split each zone into (for example) 7a and 7b, each one referring to 5 degrees Fahrenheit rather than 10 as in the larger planting zones. The Aden Earth map takes the USDA a/b map and renumbers it, putting it onto a global scale. Unfortunately, it only goes up to USDA zone 11, making it less useful for those in Central America, South America, and Africa.
Plant hardiness zone maps have several drawbacks, the first being how the maps are constructed.
In the US, the maps are a recording of the average lowest temperature over a period of many years. If you live right at the border to the next lower zone, have a plant that can just barely tolerate your zone, and have a unusually cold winter, your plant might not survive without protection. So you can't take the map at face value.
The other problem is that the map doesn't take into account the effects of snow cover. Snow insulates plants, acting just like a blanket. If you live in an area that is under snow all winter, your plants will do much better than those areas with no snow even if you live in the same zone, especially if you have high winds. The lower your zone number, the more this will have to be accounted for.
In any zone, however, you have to watch your plants carefully if you live in an area that is very windy during the winter, because the wind can dry your plants out and kill them even in a zone they should be able to survive.
I hope these maps have been helpful to you. If you have found a new or better one, please contact me!
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