USDA Hardiness Zone Map          https://planthardiness.ars.usda.gov

 

Virginia Tech publications:            http://pubs.ext.vt.edu/

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American Horticultural Society:     https://ahsgardening.org/the-american-gardener/

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Edith J. Carrier Arboretum at JMU:    https://www.jmu.edu/arboretum/index.shtml​

 

Missouri Botanic Garden:              http://www.missouribotanicalgarden.org/

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United States Botanic Garden:      https://www.usbg.gov/

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Chicago Botanic Garden:              https://www.chicagobotanic.org/