Hardiness zones are based on average minimum low temperatures which are one crucial factor in determining what plants can survive in your garden. In 2012, the USDA updated its Plant Hardiness Zones Map for the first time since 1990 based on newer and much more extensive data as well as the use of sophisticated mapping algorithms.
The range of hardiness zones we recommend can be found at the end of each bulb’s description and in our comparison charts. We tend to be conservative with these in order to help assure your success.
The letter “a” in our recommendations refers to the cooler, northern half of each zone, while “b” refers to the warmer, southern half.
“WC” in our recommendations refers to the West Coast where milder summer temperatures allow some bulbs to thrive beyond the zones recommended for the rest of the country. For example, 8b(10bWC) means the bulb should do well through zone 8 in the Rockies and east, but through zone 10 along the West Coast. But some bulbs such as tulips need extended cold to bloom, so for them there’s no West Coast advantage.
The Sunset Western Garden Book offers some regional guidance on bulbs, and we highly recommend Scott Ogden’s Garden Bulbs for the South.
Local experts can help guide you, too. See our “For Local Advice.”