When someone says a plant is rated to Zone 6, it means it will generally not survive the winter below -10°F (-23°C). Sometimes, however, you'll read where a plant is rated between two zones (e.g., Zone 5 to 9). By that it means the plant can survive to -20°F (-29°C) in winter, but the summer temperatures found in Zone 9 will be too warm for the plant to survive. That is, the plant will consume more energy trying to survive than it can create with its normal metabolic processes. The upper limit temperatures are not represented.

For those outside this area, you can compare your average temperatures to the following table: