26 JanNew USDA Hardiness Zone Map Unveiled

The long awaited update of the USDA Plant Hardiness Zone Map was unveiled yesterday. The new map is based on 1976–2005 weather data. Each zone represents the mean extreme minimum temperature for an area, calculated from the lowest daily minimum temperature recorded for each of the years 1976–2005. The previous edition published in 1990, was drawn from weather data for 1974–1986. The longer period (30 years) of data should provide a picture that smoothes out the fluctuations of year-to-year weather variations.

The new map adds two new zones 12 and 13 in Hawaii and Puerto Rico. The new map has a much finer scale than previous editions and differentiates between cities that tend to stay warmer and surrounding areas. At first glance it appears most areas are now about a half a zone warmer than they used to be. The new map is also searchable by five digit zip codes.

The new map looks like it will be a definite improvement over the previous edition and will provide a more accurate picture of plant hardiness zones.