If you’ve spent any time on our website, or read any of our catalogs, 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 US Department of Agriculture (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 temperatures. 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 map is that a gardener may look up his or her hardiness zone and use it to identify plants that will thrive in their area. For example, a gardener in Northwest Connecticut (hardiness zone 5) may confidently plant a variety that has been rated hardy to zone 4 but would generally not plant a variety that is rated hardy only to zone 6, because the zone 6 plant is not likely to survive the typical winter in that area.
How To Find & Use Your Hardiness Zone on WhiteFlowerFarm.com
First, go to www.whiteflowerfarm.com. At the top of our home page, just under the Search box, click on Find Your Hardiness Zone and enter your zip code in the box that appears, then click on Look Up. When the page reappears, your zone number will be listed at the top of the page (in the spot previously occupied by Find Your Hardiness Zone). As you navigate our site, 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.
If you choose a plant or plants that are not considered hardy in your zone, our site will offer a gentle warning at checkout. This is not intended to dissuade you (in fact, plants can sometimes be “pushed” to grow outside their hardiness zones), but we wish to help you avoid any possible disappointment if a plant fails 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 (the ‘S’ being for ‘South’) and the 10W (‘W’ for ‘West’) 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.