Climate Zones and Chill Hours
Understanding and knowing your Climate Zones and Chill Hours will prove beneficial for the best gardening experience.
Climate Zones are divisions of the Earth’s climates into general climate zones according to average temperatures and average rainfall. The three major climate zones on the Earth are the polar, temperate, and tropical zones.
|Zone 3||Zone 4||Zone 5||Zone 6|
|Zone 7||Zone 8||Zone 9|
Chill hours are the chilling requirement of fruit computed from the minimum period of cold weather after which a fruit-bearing tree will blossom. It is often expressed in chill hours, which can be calculated in different ways, all of which essentially involve adding up the total amount of time in a winter spent at certain temperatures.
Climate Zones - USDA Cold Hardiness Zones
The Climate Zone (USDA hardiness zones) offer a guide to varieties that will grow well in certain climates. Each zone corresponds to the minimum winter temperatures experienced in a given area. For best results, make sure that your hardiness zone lies within the zone compatibility of the variety that you are considering.
Great for the East
The USDA map does a fine job of delineating the garden climates of the eastern half of North America. That area is comparatively flat, so mapping is mostly a matter of drawing lines approximately parallel to the Gulf Coast every 120 miles or so as you move north. The lines tilt northeast as they approach the Eastern Seaboard. They also demarcate the special climates formed by the Great Lakes and by the Appalachian mountain ranges. (Citation: Website – The National Gardening Association)
Zone Map Drawbacks
But this map has shortcomings. In the eastern half of the country, the USDA map doesn’t account for the beneficial effect of a snow cover over perennial plants, the regularity or absence of freeze-thaw cycles, or soil drainage during cold periods. And in the rest of the country (west of the 100th meridian, which runs roughly through the middle of North and South Dakota and down through Texas west of Laredo), the USDA map fails. (Citation: Website – The National Gardening Association)
Problems in the West
Many factors beside winter lows, such as elevation and precipitation, determine western growing climates in the West. Weather comes in from the Pacific Ocean and gradually becomes less marine (humid) and more continental (drier) as it moves over and around mountain range after mountain range. While cities in similar zones in the East can have similar climates and grow similar plants, in the West it varies greatly. For example, the weather and plants in low elevation, coastal Seattle are much different than in high elevation, inland Tucson, Arizona, even though they’re in the same zone USDA zone 8. (Citation: Website – The National Gardening Association)