Hardiness Zone Map

-40 to -30º F
(-39.9 to -34.5º C)

-30 to -20º F
(-34.4 to -28.9º C)

-20 to -10º F
(-28.8 to -23.4º C)

-10 to 0º F
(-23.3 to -17.8º C)

0 to 10º F
(17.7 to 12.3º C)

10 to 20º F
(-12.2 to -6.7º C)

20 to 30º F
(-6.6 to 1.2º C)

30 to 40º F
(-1.1 to 4.4º C)

One of the most common questions I receive from fellow gardeners is "What hardiness zone do I live in and what the heck is a hardiness zone anyway?"

Well, it is an important question in helping decide what plants to use in your garden. You see, all plants are cold tolerant to a certain temperature and unless you plan on treating a plant like an annual, meaning that it will only live one growing season, you need to know if it will survive through the winters in your area. This is especially important with big-ticket items like trees, shrubs and roses.

To help gardeners with this information the U.S. Department of Agriculture developed the Plant Hardiness Zone Map. This map divides the continent of North America into 11 regions or zones. The average coldest temperature for that region determines each zone. The coldest zone is zone 1, which includes areas such as the extreme northern parts of Canada, parts of the Yukon Territory, and the Alaskan interior. Average lows are about – minus 50 degrees F in zone 1 (now that’s cold!). Zone 11 is the warmest zone with average low temperatures being 40 degrees F. The other zones fall in between these extremes. What this means is that if you buy a plant that is cold tolerant to zone 7 and you live in zone 5, that plant is not going to make it through the winter.

In addition to the Plant Hardiness Zone Map, many people also reference the American Horticulture Society's Heat Zone Map, which helps you determine if a plant will survive the summer weather in your area. The AHS explains the map this way:

"The 12 zones of the map indicate the average number of days each year that a given region experiences "heat days"-temperatures over 86 degrees (30 degrees Celsius). That is the point at which plants begin suffering physiological damage from heat. The zones range from Zone 1 (less than one heat day) to Zone 12 (more than 210 heat days)."

You can learn more about the Plant Hardiness Zone Map and the Heat Zone Map on the AHS's website, www.ahs.org. Click on "Gardening Q and A."

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