At first glance, my northeast-oriented front yard looks fairly uniform, but it is actually divided into dozens of microclimates (those places in the garden where hours of sunlight, temperature, soil type or water availability differ, sometimes markedly, from the prevailing conditions). A series of raised rock gardens and a low rock wall that faces northeast, directly east, then northeast again along its serpentine route create some of the most dramatic shifts.
Other microclimates are less apparent, formed by areas of differing soils, where beds are outlined by hardscape, by permanent shade beneath trees or shrubs, by temporary shade cast by large perennials and ornamental grasses, or where I irrigate more or less frequently. Each variable meets the needs of a different group of plants and expands my planting options.
While there are shaded and sunny microclimates woven throughout, the front yard’s macroclimate is moderated by the house itself, which acts much like a butte on the plains. Overall conditions are much gentler here than in the brutally hot backyard, where desert plants flourish. Temperatures may be a full 10 degrees cooler in the front yard, and water evaporates there much more slowly because the house shades the beds for at least part of the day.
The garden directly in front of the house, a space approximately 40 by 40 feet, has wide borders of heavily amended clay surrounding a flagstone terrace. The soil beneath the flagstone was left “as is” when I killed the lawn that once covered the front yard. The borders are mixed and contain a variety of trees, shrubs and roses, plus traditional garden perennials like Shasta daisies and wildflowers with meadow and tallgrass prairie origins such as Kansas gayfeather, Liatris spicata. These borders are watered once a week.
The flagstone terrace, irrigated only once or twice a month, is home to plants from drier origins such as golden flax (Linum flavum), moss phlox (P. subulata), veronicas and thymes. But again, the device of adding microclimates is at work here. In one area, I dug out the existing soil and replaced it with a foot of sand so that I could grow sand lovers like sea thrift (Armeria maritima). The sand bed melds seamlessly into the rest of the terrace, and the only hint the soil is different is the change in flora.
Probably the best illustration of the effect microclimates have on plants becomes obvious in May when a self-sowing population of golden columbine (Aquilegia chrysantha) pops up exclusively in shady areas of the front garden. This plant, which comes from the canyonlands of the Southwest, never ventures into full sun. At the same time, just a few feet away, a sun-loving blue-purple hybrid columbine has spread throughout the flagstone terrace. The seeds of these two columbines clearly germinate only in their preferred ecological niche.
Were conditions uniform throughout this space, I could probably grow blue columbines or yellow ones, but not both.
Marcia Tatroe is a gardening writer and lecturer. Her most recent book is “Cutting Edge Gardening in the Intermountain West,” ($29.95, Johnson Books). E-mail her at rltaurora@aol.com.
