USDA Plant Hardiness Zone Guide
| |
Zone 1 |
Below -50 F |
|
Zone 2 |
-50 to -40 F |
| |
Zone 3 |
-40 to -30 F |
|
Zone 4 |
-30 to -20 F |
| |
Zone 5 |
-20 to -10 F |
|
Zone 6 |
-10 to 0 F |
| |
Zone 7 |
0 to 10 F |
|
Zone 8 |
10 to 20 F |
| |
Zone 9 |
20 to 30 F |
|
Zone 10 |
30 to 40 F |
Most gardeners are familiar with the U.S. Department of Agriculture's Plant Hardiness Zone Map. First published in 1960 and updated in 1990, this map is based on average annual minimum temperatures recorded throughout North America. By using the map to find the zone in which they live, gardeners are able to determine what plants will "winter over" in their garden because they can withstand these average minimum temperatures.
Although these zones are useful as an indicator of a plant's likelihood for survival in a given area, many factors, including soil type and fertility, soil moisture and drainage, humidity, and exposure to sun and wind determine a plant's growth and success or failure in its enviroment. Today, nearly all American reference books, nursery catalogs, and gardening magazines describe plants using USDA hardiness zones.
Microclimates
The USDA zone map doesn’t guarantee a definite average minimum temperature. Microclimates are small areas inside a zone that are a little warmer or cooler than the surrounding area. There are factors to take into consideration. Hills, valleys and windbreaks change the flow of air. A change in air flow can cause warmer or cooler air to be trapped in an area, or move out around that area. Buildings will absorb heat during the day and release it into the evening and night (radiant heat), keeping that small area a little warmer. If you're unfamiliar with the microclimates in your area you should ask other local growers to share their information.
USE MAP ONLY AS A GUIDE
Many variables determine a plants true adaptability including rainfall, humidity, soil, elevation, light, age and cutural maintenance. ZONE MAP does not determine plants adaptability to given locality but indicates minimum expected temperatures for region and how it relates to a plant's chances of survival at that temperature.
Many plants can be grown in one zone "colder" than rated by simply placing in a protected location or by proper winter care (such as mulching). A southern exposure protected from winds will often allow one to plant specimens normally expected to grow only in warmer climates. Many houses have areas protected by two sides of an "L" and that protected spot will act ten degrees warmer than the open yard, even in the coldest weather.
Do not be discouraged from attempting to grow a "Zone 5" plant in "Zone 4", or a "Zone 3" plant in "Zone 2". Just try to think of a spot in your landscape that is a little more protected.
Zone Finder
Enter your zip code in the form below, and we'll tell you where you fall in the Arborday.org Hardiness zones database.
|
