Learn about landscape plant hardiness zones to help you select trees, shrubs, perennials, bulbs, and annuals for your outdoor spaces as you page through plant books and plant catalogs.
What is Plant Hardiness?
The United States Department of Agriculture (USDA) is the developing agency of the hardiness map. Basically, the hardiness of a plant refers to it’s capability to thrive and survive in a specific minimum temperature. The USDA divided the United States into areas, or zones (numbered 1 – 11), determined by ranges in minimum temperatures.
Thus all plants are associated with the specific hardiness zone that a plant can survive in. For example, if a landscape plant is designated as a Zone 3 plant, then that means that plant is capable of surviving in the minimum temperature that would occur in Zone 3 (Zone 2 minimum temperature would be too cold for it to survive through the winter). Therefore, the plant is hardy in Zone 3. But, that plant would also survive in the milder zones south of Zone 3. Landscape plants are not only affected by the winter cold but also may have limits as to how much heat (high temperatures) they can withstand. When you see a zone designation in a plant nursery stock book or catalog, this is what that designation is referring to.
Other countries all over the world have adopted our USDA plant hardiness mapping concept for their own country. To see the hardiness zone maps for the United States and other parts of the world, look in our Garden Links section.
