By Wendy Diaz, EMGV
A couple of weeks ago, during the peak of our latest heat wave here in the Piedmont of North Carolina, friends asked me about brown stems on their new foundation shrubs Cryptomeria japonica Dragon Prince ™ which they purchased at a local nursery and planted this spring (Photo). These compact attractive shrubs were not established, but they were watered regularly in order to sustain them through their first year in this location with exposure to afternoon-sun in a west-facing front flowerbed.
We ruled out lack of water as the culprit and suspected that the location of the shrubs in front of their new low-emissivity reflective windows could possibly be the reason for the browning of the shrubs foliage (Photo 2). I asked my friend to measure the temperature at the shrubs location and in the early evening it was over 140 degrees Fahrenheit.
On closer examination it was observed that the bottom part of the brown stem tip, closer to the trunk of the plant and more sheltered from the surface, still appeared to be green and healthy (Photo 3). A rigorous scientific study was not conducted as part of this article but circumstantial evidence of a thermometer reading over 140 degree Fahrenheit certainly leads one to believe that the intense heat caused by the suns rays reflecting off low-E windows could be the cause of the plant’s distress.
Could the shrubs brown crowns be the unintended consequence of making changes to the energy efficiency of our homes by causing another problem to the outside home environment during the more frequent intense heat waves? Low-emissivity (low-E) coatings are transparent and improve the efficiency of the glass by reflecting heat out but still letting in light. The coating is applied to the outside glass to reflect the sun’s heat out. It has been reported that heat generated from double paned low-E windows reflecting sunlight was measured in excess of 200 degrees Fahrenheit.
A possible choice to replace the front foundation shrubs may not be an evergreen non-native but perhaps a native Yucca filamentosa with some ground cover of Indian blanket flower(Gaillardia pulchella). The Cryptomeria japonica shrubs were dug up and re-potted and moved away from the low-E windows to prevent further damage awaiting replanting in the fall. Evidently some do not like it hot!