What is my Plant Hardiness Zone and why should I care?

For zip code 02129, Charlestown MA, the zone is 6b. What does this mean?

According to the USDA, "The 2012 USDA Plant Hardiness Zone Map is the standard by which gardeners and growers can determine which plants are most likely to thrive at a location. The map is based on the average annual minimum winter temperature, divided into 10-degree F zones."

By knowing your zone, you can look up plants or varieties that thrive well and purchase them for your garden. So now maybe you realize why that tropical plant, suited best for zone 11a died the second you brought it home. Here are some more helpful links to explore.