Email
PrintA Site to Behold
Our region’s microclimates depend on elevation, aspect, proximity to canyon breezes, and more
When I went land shopping in Teton Valley, Idaho, more than a dozen years ago, my realtor understandably had trouble envisioning my dream property. No, I didn’t want knockout views of the Teton peaks or an intimate mountain setting where I could watch wildlife from my deck. What I longed for was a spot where I could grow a beautiful and productive garden.
For the decade prior to my shopping trip I had gardened in the most inhospitable domain: a north-facing hill at 6,800 feet above sea level in the Snake River Range south of Wilson, Wyoming. At the end of my first gardening summer, reality hit with a ten-degree hard freeze and two feet of snow by Halloween. When my garden reappeared with late May snowmelt, I came to grips with the limitations of my chosen site. Yet for years I persisted and grew food and flowers for the few short months of mountain summer I was blessed with. But imagine the potential of a garden with just a little longer season, a more benevolent microclimate.
My land search was fruitful, and now I have a home and garden at the mouth of a beautiful canyon, where sixty-year-old apple orchards indicated its promise. Teton Valley and Jackson Hole are peppered with such tiny topographic pockets, or microclimates, where conditions favor cultivation (or make success a challenge). A scrutiny of local microclimates can help gardeners evaluate landscapes and garden sites or choose new ones. For gardeners transplanted to the Rockies, a realistic assessment of microclimate may ease the transition to choosing less risky plants for flower or vegetable gardens. Meanwhile, regionally experienced gardeners should look at their sites to avoid the “keep up with the Joneses” game: they might discover they’ve been unfairly comparing their garden with one situated in more forgiving topography.
Perhaps the most striking characteristic of gardens in the northern Rockies is the jig-saw-puzzle variability of their terrain. As one Montana grower commented, “The climate here changes every mile or so.” With growing conditions marginal anyway in the region’s short, high-altitude summer, even subtle changes in geography compound gardening challenges.
First, consider elevation. A few hundred feet makes a significant difference in evening temperatures on a summer night. But altitude isn’t everything, and more complex interactions of slope and airflow can create different microclimates at similar elevations. Frequently, a lower elevation site is actually more frost-prone. The critical fact here is that cold air sinks (as air cools, it becomes denser than warm air). When the chilly air of a high-altitude evening flows down a slope, it puddles in dips and depressions, causing frost pockets when the temperature falls. River bottoms are the classic example—they’re not the place for a tomato patch. In Teton Valley, seemingly benign elevation changes from the Teton River to the foothills of either mountain range make for a temperature difference of several degrees, as local farmers can attest. Jackson Hole slopes to a lower elevation at its western edge by the Snake River, creating a frosty region encompassing Wilson and the West Bank.
Given the phenomenon of cold air moving downhill, slope sides are preferred, whether they’re facing north or south. Due to cold air drainage, even a slight slope will be less likely to harbor frigid air. But given a choice, select a south-facing hill for a high-altitude garden: the soil needs the solar heat. “An incline of 5 degrees toward the north reduces soil temperature about as much as moving 300 miles of latitude in the same direction,” the late Frank C. Craighead, Jr. wrote in For Everything There is a Season: The Sequence of Natural Events in the Grand Teton-Yellowstone Area.
Once air gets rolling down a slope, there’s an even better microclimate found at the end of its descent, the canyon mouth. “The canyon acts like a chimney,” explains Jackson resident Jim Woodmencey, a meteorologist at www.mountainweather.com and author of Reading Weather. “In the day, warm air rises up the canyon and at night, cooling air flows down.” These constant canyon breezes stir things up, and settling cold air layers are mixed with warm air layers on top. “As a general rule, when winds are over 5 miles per hour, no frost forms,” Woodmencey says. Differential heating of canyon walls, especially over a short distance, can also create air movement. Sunny sides of a canyon heat up more than shady sides. This effect is most pronounced in narrow steep canyons. The result of these dynamics is a continuous airflow that prevents any pooling of cold air, keeping nighttime temperatures elevated.
Gardens in these fortunate locales are protected from frosts on many nights when those of neighbors by the rivers succumb. Some prime garden spots include the base of Cache Creek Canyon in Jackson Hole, lands around Alpine, Wyoming, and especially property in the vicinity of Victor, Idaho, where Teton Pass and Pine Creek Pass adjoin. Here, as Woodmencey points out, different canyon orientations create airflow at varying times of the day, all for the benefit of lucky local gardeners.
Though less prominent a feature in the Teton region, lakes can also drastically affect the microclimate. Flathead Lake in Montana, a huge natural feature, is the best regional example. It sits like a jewel in the midst of miles of bountiful fields and orchards. Large bodies of water like Flathead have a moderating influence by retaining warmth and buffering temperatures in the surrounding area. “Lakes don’t heat up or cool down as quickly as land does,” Woodmencey explains. “Differential heating, like in a canyon, between land and water, also creates airflow.”
With the big picture in mind, let’s take a look at “nanoclimates.” These are the mini-microclimates that abound at every curve of home sites and properties. A clever gardener uses them to her or his benefit, planning which plants will thrive in certain spots. Look at orientation first. A north-facing deck will typically be plunged in shade while, simultaneously, the south side of a house cooks in the midsummer sun. Obviously, each area calls for distinct plant choices. Looking for a place for those precious tomatoes? Construct a cold frame or mini-greenhouse on the south wall of the house or garage. One gardener in the Green River Valley outside Pinedale, Wyoming, grew early spring greens in such a structure—while the rest of her property was covered with snow.
Other terrain and landscape features can also create warmer or cooler nanoclimates. Be watchful of any sinks or depressions and steer frost-sensitive plants away. Even a berm or hill can create diverse exposures, with shady and sunny orientations. While a little wind is a good thing, a blast is not healthy for man or plant, and a well-situated fence can reduce dehydration and stress caused by too much breeze. One very green-thumbed gardener in Jackson Hole had a small south-facing yard bordered by a medium-height fence. He nonchalantly grew ample crops of sweet basil, unaware of the benevolent nanoclimate created by both his fence and southern orientation. A creative look around your yard may reveal similar possibilities. By observing nanoclimates with a discerning eye and selecting plants accordingly, you can optimize their chances for success in an already challenging environment.
Early every summer morning, I delight in the steady breeze, rich with the scent of pines from miles upwind, coming down my canyon. It’s a harbinger of the sweet corn, pumpkins and gladiolas I anticipate each fall. As residents of the Northern Rockies, we love our mountain homes, and we love our gardens. With an eye to microclimate, it’s not a paradox after all.
Author Judy Allen now shares her Teton Valley microclimate at the mouth of Darby Canyon, renting garden plots to anyone interested in escaping valley frosts and growing fresh produce all summer long. Each fifty-square-foot bed has been enriched with compost and organic soil amendments for over ten years, and the garden meets national certified organic standards. Irrigation water and initial soil prep are included. New and experienced gardeners can also glean occasional tips from Judy when she's working in the garden. Call (208) 354-3199 to reserve space for next spring.
This story originally appeared in the Fall/Winter 2004–05 edition of Teton Home.
