A guide to mountain states' gardening climates - Sunset climate zone maps - Brief Article

Sunset, Dec, 2000 by Jim McCausland

Here's what the new Sunset climate zone maps tell you about gardening in your region

Taking advantage of newly available weather and climate data, Sunset has refined the climate zone maps for our next edition of the Western Garden Book, available in bookstores in mid-February 2001. Maps for the West's mountain states, as well as gardening climate descriptions, appear on these pages. Find your region on the map, then read the corresponding description of your garden climate zone.

Gardening in the mountainous West is always a challenge, but understanding your climate zone will help you grow plants successfully. In fact, climate determines what plants you can and cannot grow in your garden. Once you know the characteristics of your zone, you can use the newly revised Western Garden Book to choose plants suited to that climate zone.

* Zone 1A: Coldest mountain an intermountain areas

Marked by a short growing season and relatively mild summer temperatures, zone 1A includes the coldest regions west of the Rockies, and a few patches of cold country east of the Great Divide. The mild days and chilly nights extend bloom of summer perennials like columbines and Shasta daisies. If your garden gets reliable snow cover (which insulates plants), you can grow perennials listed for some of the milder zones. Along with hardy evergreen conifers, tough deciduous trees and shrubs form the garden's backbone here. Gardeners can grow warm-season vegetables as long as they're short-season varieties.

Winter lows average in the 0[degrees] to 11[degrees]F (-18[degrees] to - 12[degrees]C) range; extremes range from -25[degrees] to -40[degrees]F (-32[degrees] to -40[degrees]C). The growing season averages 50 to 100 days.

* Zone 1B: Coldest plains climate

Centered over the plains of Wyoming and Montana, this zone sees January temperatures from 0[degrees] to 12[degrees]F (-18[degrees] to -11[degrees]C), with extremes between -30[degrees] and -50[degrees]F (-34[degrees] and -46[degrees]C). Zone 1B lies east of the Great Divide, where the continental climate reigns supreme. Arctic cold fronts sweep through 6 to 12 times a year, sometimes dropping temperatures by 30[degrees] or 40[degrees]F in 24 hours. The summer growing season tends to be warm and generous at 110 to 140 days long, but constant winds-12 mph average, year-round, in many places--call for windbreaks and shade trees, such as hackberries and cottonwoods. Few shrubs are better loved here than lilacs or better adapted than smoke tree. With protection, annual vegetables and flowers thrive, as do wind-tolerant perennials like buckwheats, grasses, and penstemons. Where winters are dry and snow cover light, gardeners compensate with mulch and extra water.

* Zone 2A: Cold mountain and intermountain areas

Another snowy winter climate, zone 2A covers several regions that are considered mild compared to their neighbors. This zone stretches over Colorado's northeastern plains, a bit of it along the Western Slope and Front Range of the Rockies, and in mild parts of river drainages such as the Snake, Okanogan, and Columbia. It also shows up in western Montana, Nevada, and in mountainous areas of the Southwest. This is the coldest zone in which sweet cherries and many apples grow

Winter temperatures usually hover between 10[degrees] and 20[degrees]F (-12[degrees] and -7[degrees]C) at night, with drops between -20[degrees] and -30[degrees]F (-29[degrees] and -34[degrees]C) once every few years. When temperatures drop even lower, orchardists can lose their trees. The growing season is 100 to 150 days.

* Zone 2B: Warmer summer intermountain climate

A good balance of long, warm summers and chilly winters makes this a perfect zone for commercial fruit growing, which is why you'll find orchards in this zone in almost every state in the West. You'll also notice this snowy-winter climate along Colorado's Western Slope and mild parts of the Front Range, in Nevada from Reno to Fallon and north to Lovelock, in large parts of northern Arizona and New Mexico, and in mild parts of the basins of the Columbia and Snake Rivers.

Winter minimum temperatures are milder than in neighboring zone 2A, averaging from 12[degrees] to 22[degrees]F (-11[degrees] to -6[degrees]C), with extremes in the -10[degrees] to -20[degrees]F (-23[degrees] to -30[degrees]C) range. The growing season ranges from 115 days in higher elevations and more northerly areas to more than 160 days in southeastern Colorado.

* Zone 3A: Mild intermountain areas

East of the Sierra Nevada and Cascade Range, you can hardly find a better gardening climate than zone 3A. Winter minimum temperatures average from 15[degrees] to 25[degrees]F (-9[degrees] to -4[degrees]C), with extremes between -8[degrees] and -18[degrees]F (-22[degrees] and -28[degrees]C). Its frost-free growing season is 150 to 186 days in a normal year. The zone tends to occur at lower elevations in the northern states (Idaho, eastern Oregon, and Washington) and at higher elevations as you move south to Utah's Great Salt Lake and into northern New Mexico and Arizona. Fruits and vegetables that love long, warm summers--melons, gourds, and corn--typically do well here. This is another great zone for all kinds of deciduous fruit trees and ornamental trees and shrubs, as long as you water them well in summer.