Observations on Climate Change by Dennis McGlade

Top Left: Tradescantia pallida observed in Philadelphia in early April 2012. Top Right: Tradescantia pallida in full-bloom in warm climate. Bottom: Mass of Tradescantia pallida in warm climate.

Throughout my professional experience as a landscape architect and gardener, I have worked in some of the world’s warmest climates, such as southern California, Florida, Barcelona, Mauritius and the Cayman Islands, and I have developed a knowledge of plants that flourish in tropical weather. This past spring season I observed plants growing in Philadelphia that typically only survive in warmer climates. This can be viewed as anecdotal evidence of climate change.

In early April, I was on my way into our studio when I walked by a planter on the sidewalk that I have passed every day on my way to work for the past several years. Every summer the owners fill the planter with annuals and then leave them to meet their frosty demise in the fall. This year to my dismay, a Tradescantia pallida (called by the common name Purple Queen/Purple Heart) was sprouting from a non-descript clump of last year’s foliage. This plant was originally planned for summer 2011 display; however, to my surprise it had survived the winter and looks to produce another show this season. In my experience, this purple leaved vine forming plant—which is native to the frost-free tropics—is usually killed by northern winter freezes. According to the 2012 USDA Plant Hardiness Zone Map, Tradescantia pallida has a Zone of 8 to 9a on a scale of 1 through 11 (11 representing the warmest climate), while Philadelphia is identified as a cooler Zone 7b region.

Another local example of climate change is the presence of Lagerstroemia indica (Crape Myrtle) Magnolia grandiflora (Southern Magnolia) and Camellia japonica hybrids (Camellia), now growing rather commonly in Philadelphia. I moved to Philadelphia in the late 1960s to attend graduate school at The University of Pennsylvania under the flamboyant tutelage of renowned landscape architect and writer Ian McHarg. At that time, crape myrtle was solely found on the Delmarva Peninsula of Delaware and along the southern New Jersey Atlantic coast around Cape May. Southern magnolia only flourished on the south and east side of taller buildings that gave them winter protection. Back then, I do not recall ever seeing a Camellia japonica hybrid growing outdoors in Philadelphia. Today, all three of these plants grow outdoors here—along with hardy bananas and one or two palm trees tucked into particularly protected microclimates. I wonder what’s next…perhaps fried plantains will replace fried onions on our beloved Philly cheesesteaks!

by Dennis McGlade, Partner, RLA, FASLA May 22, 2012 Topics: Recent Work, Dennis McGlade