Hardiness Zones

If you've spent time on our website or reading any plant catalog, you've encountered the concept of a "plant hardiness zone." We'd like to de-mystify this term a bit and explain how your location should play into your selection of plants.

What Is a Plant Hardiness Zone?

Using historical temperature data, the USDA divides the country into 13 plant hardiness zones, ranging from 1 (coldest) to 13 (warmest). Each of these zones is further divided into “A” and “B” for greater precision, with A being colder than B. These zones are defined by average annual minimum winter temperature. For example, a zip code in which the average annual lowest winter temperature is between -15 and -10 Fahrenheit is assigned to hardiness zone 5b. The plant hardiness zone map is shown above and further information about how the map is assembled and maintained is available at USDA.gov.

Gardeners can look up their hardiness zone by zip code and use it to identify those perennial plants which can be expected to successfully overwinter in their area. For example, a gardener in Northwest Connecticut (hardiness zone 6a) will confidently plant a variety that has been rated hardy to zone 4 but may not choose a variety that is only rated hardy to zone 7, because the zone 7 plant would not be expected to survive a typical winter Zone 6 winter. 

How to Use Your Hardiness Zone on WhiteFlowerFarm.com

Look up your hardiness zone by entering your zip code in the "Find Hardiness Zone" box at the top of this page. Then, as you navigate our site, use the filters on the left side of the page to narrow down our plant offering to those varieties that we rate hardy for your zone.  

Shortcomings of the Plant Hardiness Zone System

The Plant Hardiness Zone system is useful and widely adopted but it has significant limitations, including:

• It's based on historical averages and winter temperatures are highly volatile.
• It indicates only a plant's expected cold tolerance - not its ability to withstand heat or drought, its preferred soils and moisture levels, or any of the other variables that bear on a plant's success in a given site.
• Many gardens contain "microclimates" where topography, light levels, and other factors give rise to conditions that differ from the rest of the garden.

We find that our customers, over time, gain an anecdotal understanding of which plants do and don't work for them, and that this hands-on experience is much more helpful than a strict reliance on hardiness zone. When in doubt, please contact us - our knowledgeable customer service team is standing by to help.