Each plant has two numbers besides the

 Growing Zone,

For Example: 6-9.
This means the plant will grow in

Zone 6, 7, 8 and 9.

Please Note: There are many variables involved in plant hardiness. Please use the best information available to you to provide cold hardiness zone information on plants you might want to add to your collection.

 Zone maps are bases on multi-year temperature data. Maps using data from recent, milder winters have shifted many areas one zone warmer. To further complicate matters, in any given year temperatures can fluctuate a zone or even 2, up or down. Such factors as lack of snow cover, early or later extremes and protections from mulch or buildings can also have an effect. If you have any questions about plant hardiness, contact your local state land grant university, County Extensions Office.