Gardeners love to talk about the weather and have a tendency to lament whatever weather comes our way – it’s too hot, too wet, too dry, or too cold, and every variation carries with it concern about its impact on our gardens. Give us two days of warm weather in early spring and we are already worried about how we will protect our plants from extreme heat. This season, however, I decided to stop feeling so helpless and to do something in the garden and in my house to counteract the summer heat. About eleven percent of American energy use goes to heating and cooling our homes. Last week, I wrote about creating windbreaks to mitigate my heating bills and carbon footprint. This week, having finally met with an architect to plan the renovations on my house, I am thinking about how I can keep my house cool.
Even though the last few summers have been among the hottest on record, I do not have air conditioning and want to keep it that way. My architect smartly suggested that I at least cost out the price of central air, with the idea that I could install it either now or later, if the warming trends, which our current President is denying, should continue. This is sound advice and much appreciated, but I could not help but think that, if I can plant a windbreak to keep my house warmer in winter, could I also use plantings to keep my house cooler in summer? If I am to invest in green energy, I’d rather it be in plants than in energy-efficient cooling systems.
In temperate regions of our country, the rules for keeping a house cooler in the summer are quite straightforward. First, provide summer shade for roofs, windows, and east and west facing walls. Second, funnel summer breezes towards the house. But it is also important to make sure to coordinate what works for winter cold with what works for summer heat. The plantings on the north side of my house to deflect winter winds are evergreen as they are not in the path of the winter sun, but I need to take a different approach in selecting plants to provide summer shade to the south, east and west of the house so I can take advantage of the sun’s rays in the winter. The best answer seems to be deciduous plantings that provide cooling effects in the summer, but have leafless winter forms that allow the winter sun to reach the walls and roof of my house. And while we all think of stately, tall shade trees, such as elms and oaks, as the ultimate providers of shade, we need to recognize that shrubs, small trees, and even vines can also work to shade the west and east side of the house and to keep direct sun from pouring through windows.
The west side of my house is currently sheltered by an allee of beautybush and a flowering cherry, as well as a climbing hydrangea that scurries up the walls and fireplace chimney, leafing out as the weather warms up just in time to provide the necessary cooling effects. Vines and fast-growing shrubs are useful for getting the process going quickly and are well suited for shading west- and south- facing windows. But as with all environmental issues, it is ideal to plan for the long-term, and large shade trees are the best investment for reducing future energy usage. Large shade trees cool in several ways: they keep the ground cool by preventing the sun’s rays from making direct contact with the soil; their foliage does not trap and radiate heat the way stone and metal do; and, lastly, they lower temperature by releasing water vapor from their leaves, a process known as evapotranspiration.
Shading a driveway or a terrace from summer sun, particularly if made from asphalt or dark stone, can reduce the ambient temperature by as much as 25 degrees Fahrenheit on a sunny day. Similarly, roofs shaded from summer sun can help keep indoor temperatures 8 to 10 degrees cooler. Planting a six-to-eight foot tree can help shade windows in its first year and, depending on the siting and the species, should be shading the roof in eight to 10 years (most likely coinciding with the end of the life-cycle of that new air-conditioning unit that I hope not to purchase.) Incidentally, providing shade for an air conditioning unit, which can be accomplished through strategically placing plants around it while allowing for proper air circulation or simply siting it on the north side of the house, can reduce its energy usage by as much as 10 percent.
So, as I await my house plans and construction cost estimates, I am looking up the price of air conditioning systems on the Internet and seeing how I can spend that budget at the nursery instead. Either way, I am not going to break a sweat, except perhaps when I put shovel to earth.
A gardener grows through observation, experimentation, and learning from the failures, triumphs, and hard work of oneself and others. In this sense, all gardeners are self-taught, while at the same time intrinsically connected to a tradition and a community that finds satisfaction through working the soil and sharing their experiences with one another. This column explores those relationships and how we learn about the world around us from plants and our fellow gardeners.