Want To Learn About Planting Zones?

The idea behind the use of planting zones is to help you to know whether a plant will be suitable for the area in which you live. There are several kinds: hardiness zones, heat zones, and climate zones are just a few.

Hardiness zones

(January 25, 2012: the USDA has released an updated zone map which no longer shows Canada and Mexico when you click on it. For that reason I'm leaving this old map up there for those of you from Mexico until I find one for you. This map may be inaccurate: several people in the US have reported that they are in different zones now.)

Hardiness zones are areas of the country (or world) that correspond to the same minimal temperature. Hardiness planting zones are extensively used by websites, books, magazines, and other publications, to give you some idea of whether a plant can survive in your area.

A plant's hardiness zone assignment tries to tell you how much cold a plant can withstand.

At least that seems to be the intent. However, the 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 plants that can just tolerate your zone, and have a unusually cold winter, your plants may not survive without protection. So you can't take planting zones 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 must be accounted for.

In all planting zones, you have to watch your plants 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 planting zones that they should be able to survive.

Here are some more hardiness maps. Although many of them are just the USDA temperature classifications mapped onto other countries, some countries have developed their own maps. If you live in one of these countries, you should read up on how the numbering systems differ and how to translate the USDA numbering to your country's system.

Regional and specific country maps

PlantMaps is a site with interactive US, UK, and Canada plant hardiness maps, including one that was updated in 2010. Fun!

This is an experimental Canadian map without any temperature numbers, which makes it unwieldy, in my opinion, but it may be helpful to you.

An interactive hardiness zone map of Canada from HGTV.

A pdf file of the South American USDA zones. I find this difficult to read because the zones are not color-coded, just written on the map, but this show 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 map 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 the EGF have developed their own maps and zoning systems (pdf file).

Here is an interactive zone map for Europe.

Another Europe map. This one is not interactive, but shows more of eastern Europe, along with a bit of northern Africa and part of the Middle East.

A USDA map of the Ukraine.

If you're in the former Soviet Union, the Missouri Botanical Society has a detailed discussion (with maps) of hardiness zones there and how they compare to the USDA zone map.

Here are two maps for Africa:

Basically the USDA map put onto the African continent.

A USDA hardiness map put onto southern Africa

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.

A USDA map placed onto New Zealand.

USDA zones in China (the same map in pdf form, with better quality)

A pdf file with the Japanese islands mapped using the USDA system (much of this is in Japanese).

Global maps

As part of the NCSU/APHIS Plant Pest Forecast (NAPPFAST) System, the Animal and Plant Health Inspection Service (APHIS), North Carolina State University (NCSU), and the information technology company ZedX, Inc have developed a fairly detailed global plant hardiness zone map from the USDA one, adding zones 12 and 13. I actually like this one quite a bit, because of the higher zones which, of course, are not seen in the US, making this a truly global planting zones map.

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 South America and Africa.

Heat zones

The American Horticultural Society has a heat map of the lower 48 US states developed in the 1990's that you can download. However, with global warming, I wonder how accurate that map is.

Here's a heat map for Australia (pdf file). Again, this was made in the 1990's.

Until our global climate stabilizes, heat maps should be used as clues to how a plant might do in your area rather than relying on them.

Climate zones

• hot and dry (desert)
• hot and humid
• hot and wet (tropical)
• cold and dry
• cold with lots of precipitation (rain in summer, snow in winter)
• moderate temperatures with variations in rain/snowfall

and so on.

A plant that does well in one climate may not do well in another.

For example, let's take zone 7. In the United States, zone 7 corresponds to places as diverse as northern California (mild and wet, temperate), southern Nevada/northern Arizona (hot and dry, desert), and northern Georgia (hot and humid). There is no way a plant that likes northern California would ever survive in southern Nevada without a lot of watering!

(Apologies to those living in other countries, but hopefully you can see the limitations on planting zones based solely on minimum average temperature. Look at hardiness zone maps for your country if you still aren't clear on the difference between temperature and climate, or take a look at this very interesting article on climate types.)

Climate maps attempt to divide an area into planting zones that correspond to their climate.

If you look at the areas we have just been discussing, you'll see that southern Nevada is listed as desert, while northern Georgia is listed as temperate -- but on the hardiness zone map they are both zone 7. (a bigger map would be more helpful, but that's what we're given.)

Here's an interesting climate map from HowStuffWorks.com:

If you can't see the map, click here to visit the map page on howstuffworks.com.

Here's an "eco-zone" map (basically a climate map) of Canada.

Sunset zones

Sunset Magazine (a southwestern US gardening magazine) has developed a climate map for the 48 contiguous states, taking into account a variety of factors including rainfall, heat days, and so on.

If you live in the US, you can use this interactive map to find your Sunset zone and suitable plants for it. Unfortunately, most nurseries, websites, and books don't reference Sunset zones, but you can consult the Sunset website or one of their publications if you need more information.

Other types of planting zones

Annual rainfall is important to know if you don't want to have to do a lot of watering. On the other hand, some plants from very dry areas can't tolerate a lot of water.

For example, you wouldn't want to plant desert plants in a swampy area, because they would die. Knowing your average rainfall totals can help when choosing a plant for your area.

Here's an interactive US map from HowStuffWorks.com:

If you can't see the map, click here to go to the US map page.

Here's an interactive global rainfall map:

If you can't see the map, click here to go to the global map page.

Here's another global annual rainfall map.

I hope these maps have helped you. If I find more maps of planting zones, I'll let you know through my blog, Twitter, or Facebook. Click on the orange RSS button to the left to subscribe to my blog feed in your reader!

Related pages:
Outsmarting the planting zone map

One of your questions:
Zone 3 fruit trees?

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