What does hardy in Zones 4-9 mean?

When a plant is listed as hardy in Zones 4-9, what does that mean?
Submitted by BHGPhotoContest

The USDA Hardiness Zone map (see page 603) was developed by examining average minimum winter temperatures for various locations over many years. Each zone covers a temperature range of 10 F, and the lower the number, the colder the average minimum winter temperature for that site.

 

For example, plants hardy to Zone 4 should withstand the -30 to -20 F average minimum winter low temperatures experienced there. Those in Zone 9 on average experience a minimum winter low temperature of +20 to +30 F. Some winters are milder than others, so you might be able to grow a Zone 6 plant in Zone 5 for a few years. But it's likely that a severe winter will eventually hit and kill the tender tree, shrub, or perennial. The USDA zones don't take into account the idiosyncrasies of your yard. You may have a protected spot where tender plants will thrive outside their usual zone.


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