Many world-renowned gardens utilize both natural and manipulated microclimates to achieve drama and beauty. Designers of Sissinghurst Castle Gardens in Kent, England and Butterstream Gardens, in County Meath, The Irish Republic exploited existing structures like old brick walls and buildings along with natural influences such as compass direction, water, and large trees. The Isle of Wight surrounded by waters of the Solent is a "working example" of bodies of water influencing a regional or neighborhood microclimate.
Here are some major environmental features that can shape and exploit microclimates. Once you begin to recognize and look for microclimates, you start understanding what makes a successful landscape.
1. Altitude influences temperature. In general, for every 250 feet rise above sea level the temperature drops one degree. This shortens the growing season by several days in mountainous or hilly locations. Traveling north along the east coast of North America, growing seasons decrease by weeks. Edwin Way Teale's 1951 account "North with Spring" superbly chronicles these changes in the natural world.
2. Slope influences cold air drainage. Orange-red "swamp maples" (Acer rubrum) reveal low wet spots as they announce autumn in New England. Orchardists plant fruit trees on hillsides to avoid early spring frosts. Successful gardeners plant hardy or frost-tolerant stock at the bottoms of slopes.
3. Bodies of water, whether large or small, function as heat sinks. Small ones absorb daily heat and imperceptibly return it to their surroundings. Large bodies such as rivers, lakes and oceans absorb heat over long periods and successfully moderate regional climates.
North American environments along the Great Lakes have growing seasons averaging five to ten degrees warmer than areas away from the water. The Gulf Stream, originating in North America, warms coasts of Ireland, Cornwall, Wales, Brittany and Normandy allowing semi-tropical plants to thrive in these locations.
4. Compass directions, especially positions north and south, influence heat, sunlight and occasionally amounts of water. In eastern North America, south-facing slopes support populations of oak (Quercus spp.), hickory (Carya spp.), sometimes dogwood (Cornus florida) and shadbush (Amelanchier spp.); north-facing slopes support sugar maples (Acer saccharum), hemlock (Tsuga Canadensis) and other hardwoods. Evergreen trees and shrubs, planted in unprotected south-facing gardens, face winter injury or winterkill.
5. Soils influence not only what grows where, but also how plants develop and thrive. Underlying rock and weathering dictate soil types and pH. However, inconsistencies do occur. Pockets of acid-loving Rhododendron grow in some acid pockets of lime-rich England; populations of lime-loving ferns and wildflowers grow in limey patches of acid New England soil. Gardeners modify soil by applying lime to neutralize or ammonium sulfate to acidify the soil.
6. Microclimate changes by the presence of buildings and other structures influences more than plant survival. They factor into longer growing seasons so plants reach their peaks earlier and carry on longer than indigenous growing seasons allow.
The introduction to this series of articles is found at Environmental Factors 1.
©
Text and photographs by Georgene A. Bramlage, [March, 2006]]. Reproduction without permission prohibited
