The United States Department of Agriculture (USDA) has devised a system to provide gardeners with a basic guide to plant hardiness – how much winter cold a plant can withstand. The Hardiness Zone Map system divides the United States and Canada into numbered zones based on lowest average winter temperature. Even within a zone, different micro-climates exist, such as large urban areas which may be warmer or land situated at different elevations.
WHAT EFFECTS PLANT HARDINESS
The Hardiness Zone Map is a valuable tool but it is not foolproof. There are a variety of factors that can influence the hardiness of a given plant in a garden. These factors include: soil type, drainage, snow cover, exposure to wind, winter, rainfall (or lack of), as well as fluctuations in temperature.
HOW IT WORKS ON OUR SITE
When you are on a page with the left sidebar of filters you will find a filter for hardiness zones. If you are on a plant description page, underneath the photos you will find a "Description" box. Click the "View More" toggle and scroll down to find the zone for that plant (see below).