If you've spent any time on our website, or reading any plant catalog, you've likely encountered the term "hardiness zone." We'd like to de-mystify this term a bit, and explain how location should play into your selection of plants.
What Is a Hardiness Zone?
Using historical temperature data, the USDA has divided the country into 13 hardiness zones, ranging from 1 (coldest) to 13 (warmest). Each of these zones is further divided into “A” and “B” for greater accuracy, with A being colder than B. Click here to see the USDA's hardiness zone map. These zones are defined by average annual minimum temperature. For example, a zip code in which the average annual minimum temperature is between -15 and -10 Fahrenheit is assigned to hardiness zone 5B.
The idea behind the zones is that gardeners can look up their hardiness zone and use it to identify plants which will thrive in their area. For example, a gardener in Northwest Connecticut (hardiness zone 5) will confidently plant a variety that has been rated hardy to zone 4, but would generally not plant a variety that is only rated hardy to zone 6, because the zone 6 plant would not likely survive their typical winter.
How to Find & Use Your Hardiness Zone on WhiteFlowerFarm.com
First, enter your zip code in the "Find Hardiness Zone" box at the top of the page. Then, as you navigate our site, you can use the filters on the left side of the page to narrow down a listing to display only plants that will thrive in your zone.
Our site will offer a gentle warning at checkout if you are shipping a plant to an address outside of its suggested hardiness range—this is intended not to dissuade you, but only to avoid the possible disappointment of a plant failing to perform well due to a climate mismatch. Please be aware that we cannot honor our usual guarantee on plants that have been shipped outside of their suggested hardiness range.
Sometimes Hardiness Ratings Include "S" or "W" - What Does This Mean?
When listing the hardiness range of a plant, we often "split" the warm end of the range—for example, you might see a plant listed as Hardiness Zone: 3-8S/10W. In this instance, the 3 refers to the "cold hardiness" of the plant—all else equal, this variety should overwinter successfully in Zone 3. The 8S refers to the humid Southeast and the 10W to the comparatively dry Pacific Coast states of CA, OR, and WA—this plant can tolerate Zone 8 temperatures in the South, and Zone 10 temperatures on the West coast. In Northern climates, summer heat is not typically a consideration.
So to summarize—a plant listed as 3-8S/10W should successfully overwinter in zones 3 or warmer, tolerate humid heat up to Zone 8, and tolerate dry heat up to Zone 10.
We realize this is complicated; the problem is that the USDA zones are really not sufficiently specific. For example, our nursery in Connecticut is in the same hardiness zone as Taos, NM—a climate that could hardly be more different than ours. Furthermore, there are innumerable other variables that may determine how a plant fares in a given site. We find that customers, over time, gain a good understanding of which plants do and don't work for them, and that this understanding is much more helpful than a strict reliance on hardiness zone. When in doubt, please contact us—our customer service team is extremely knowledgeable and ready to assist.