Growing Concerns: ‘Microclimate’ an important factor in plant placement
I had the pleasure of spending last weekend camping with a group of hardy Boy Scouts in Ely. Temperatures ranged from lows of minus-32 at night up to minus-8 on the warmest day.
Wilderness survival is a skill that can only be learned by going to an outdoor classroom and surviving it. The scouts all survived and felt it was a fun learning experience. The adult leaders even enjoyed staying out in the elements to demonstrate our own resourcefulness. However, I don’t think any of us would want to do it for a living.
Unlike our scout group that spent a weekend outdoors by our own choice, landscape plants have no other option. In nature, the plants that are best suited to a particular soil, level of sunlight and other local environmental factors succeed while plants that are poorly adapted to a particular location are short-lived.
In urban environments, people choose where specific plants are going to grow. Training, experience and intuitive observation make some people very good at placing plants where they will thrive. However, most people just try to grow something they like wherever they have a space. Sometimes this is successful and sometimes not.
For our scouts, the highest priority was to seek out the best location for their recreation. They moved quickly through shaded exposed sites where they felt chilled and rested or played in sunny protected sites that offered exposure to the warming rays of the sun.
These areas are known as “microclimates.” People and animals regularly seek out or create microclimates for their own comfort. Good horticulturists and landscape designers are ever aware of these microclimates when selecting landscape plants.
For our scouts, comfort revolved around finding the warmest possible microclimate to make our time outside more enjoyable. In our region, south- or southeast- facing slopes with good protection from the north and northwest will be the most comfortable winter climate for warm-blooded species. East and northeast slopes may be more desirable in the heat of the summer.
In the plant community, south and west exposures offer a hot, dry summer environment and the widest temperature fluctuations during the winter months. This creates the harshest survival conditions for plants. North and east exposures offer more moderate temperatures and moisture regimes. Plants are not affected by wind-chill like warm blooded species, so the extreme cold we feel from our prevailing northwest winter winds are not a factor in plant survival.
Since we have hundreds of plants to consider in the urban landscape, developing the knowledge to place plants in the best locations takes lengthy study and experience. I can only illustrate with a couple of examples here.
White birch and yew are both adapted to sites with uniform soil temperatures and moisture. Hot drying summer environments and rapid fluctuations are detrimental to these species. These are two examples of plants that are best considered for north and east exposures.
Juniper and Spirea are two plants that better tolerate hot, dry and fluctuating conditions. While they would grow well in north and east exposures with adequate sunlight, they are typically used in south and west landscape exposures that less hardy species won’t tolerate.
For most homeowners, a healthy and aesthetically pleasing landscape is best achieved by enlisting the services of an experienced landscape designer. Proper plant selection and placement will provide a healthy and long-lived plant community. It will also minimize plant pest problems and environmental damage.