Heirloom Roses recommends referencing the USDA Hardiness Zone Map because it is most commonly used by gardeners, national garden magazines, catalogs, books, and many nurseries. Although it has a few drawbacks (e.g., effects of snow cover, freeze-thaw cycles, or soil drainage during cold periods, and does not account for the variety of different weather conditions within the same zone), we feel it is the most reliable source for zone information. To determine a date for receiving roses, be…
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