Image source: https://planthardiness.ars.usda.gov/ Interpreting the Plant Hardiness Zone Map Updated: 11/17/23 by Jonathan Foster, Horticulture Outreach Professional How does this Hardiness Zone Map differ from the old one? The new map is based on about 30 years of weather data, from 1991-2020, and the recommendations from a multi-disciplinary panel of experts. This recent data is