What’s the difference between zone 8 and 9?
As cited in the description of Zone 8, the biggest readily apparent difference between Zones 8 and 9 is that Zone 9, a thermal belt, is a safer climate for citrus than Zone 8, which contains cold-air basins. The zones are then broken down again into “a” and “b” zones, which have 5-degree Fahrenheit differences. Zone 9a has minimum temperatures of 20 – 25° Fahrenheit and Zone 9b has minimum winter temperatures of 25 – 30°F.