The US Department of Agriculture Plant Hardiness Zone Map, revised in 1990, shows the lowest temperatures that can be expected each year in the United States. These temperatures are referred to as "average annual
minimum temperatures" and are based on the lowest temperatures recorded for each of the years 1974 to 1986. The different zones represent areas of winter hardiness for agricultural and natural landscape plants.
For each plant we offer, we include a range of hardiness zones, for instance, Zones 3-8. This means that we think that as far as temperature goes, that a particular species when established should be able to grow
anywhere on the map between and including Zones 3 to 8. This is very general and one would need to take into account specific cultural and habitat requirements. So use a zone to determine minimum temperature thresholds and our ranges to determine broad climate tolerances.
