Why a Plant Hardiness Zone Map?
Low temperature is one of the most critical environmental limitations for plants. Some plants, like annual flowers and vegetables, simply avoid the cold of winter by dying at the end of summer. Perennial plants (including trees, shrubs and herbaceous perennials) must be able to survive the lowest temperature each winter in order to live into the next growing season. Such plants have a threshold temperature below which they will die. These threshold temperatures determine how far north plants will survive. The Plant Hardiness Zone Map of the United States Department of Agriculture (USDA) represents low winter temperatures in North America. It is a guide to help you to assess plant hardiness. What the Map Shows The map above shows the plant hardiness zones of Maine based on average yearly minimum temperatures, from data for each year from 1974 to 1986. (This time period was the most recent prior to the map s release for which reliable data were available, with most sites reporting at lea
