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Differences between 1990 USDA hardiness zones and 2015 arborday.org hardiness zones

Much of the U. S. has been warmer in recent years, and that affects which trees are right for planting. The Arbor Day Foundation has recently completed an extensive updating of U.S. Hardiness Zones based upon data from 5,000 National Climatic Data Center cooperative stations across the continental United States.

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