Hardiness Zone information helps you determine which herbaceous perennials and woody trees, shrubs and vines will survive winters where you garden.
Zones are based on the average annual minimum temperatures as determined by the USDA for the years 1974 to 1986. For example, if you garden in Zone 5a, Hardiness Zone Summary suggests you can expect that your low winter temperature may drop as low as -15 F and -20 F. Based on the list of indicator plants on that page, you can expect that flowering dogwood (Cornus florida) will be survive winters where you live, but not in colder Zones.
