Our warmer weather this fall offers one more piece of evidence, if we need it, that climate change is real. The stunning fall-colored leaves we’re used to seeing by now have yet to arrive. At least at this writing, the frost needed to start the process hasn’t occurred. The National Ocean and Atmospheric Administration (NOAA) declares DC is hotter and wetter in 2021. No wonder Capitol Hill homeowners are having success experimenting with tropical plants.
NOAA weather-tracking trends say that 90 F is our new summer normal, and our winter months are two degrees warmer measured from 1991 to 2020. These changes favor the more tropical plants like palms and banana trees.
One of the first things gardeners consider when making a design is what hardiness zone they are working in. Since 1960, the US Department of Agriculture (USDA) has provided a hardiness zone map. The zones are defined by 10 degrees’ difference in winter temperatures. The country is organized in 13 zones, and some zones are subdivided to provide even more precise information. The USDA map can be accessed online, https://planthardiness.ars.usda.gov/. Capitol Hill is a 7b zone.
Adam Pyle, horticulturist at the US Botanic Garden, calls himself a zone bender. He works with all kinds of plants in his day job. But he really becomes a zone bender at home, when he grows things that stretch the hardiness zone, like tropical plants. In the past, Capitol Hill winter temperatures have not been conducive to keeping most of these plants alive. But that’s changing.
While zones define our overall climate, gardens can have microclimates that create special warmer areas. Pyle says to look for the place snow melts first, like buildings, stone walls and south-facing slopes, to find your warmest microclimates. The front of his house is a microclimate zone.
Zone benders like to experiment. They recognize that it is possible to lose the plant, especially in an unusual cold spell. Pyle suggests not planting more than one or two zones away from the 7b zone. Many tropical plants survive winter by dying back to the ground once it gets cold. Using straw and extra mulch can provide protection that gives the plant a better chance to spring back.
But, when it’s all said and done, Pyle believes “there are no rules other than to use your imagination and have fun.”
Tropical Plants on the Hill
Banana trees are adding visual interest in Capitol Hill yards this year. With the heat and rain of July, these trees have reached 12 feet tall or higher. Whether grown in a pot or in the ground, these cold-hardy plants with giant leaves make a statement.
The musa basjoo banana tree originates from Japan, which has a climate like the Hill’s. According to Pyle, researching the origin of plants can provide a lot of information and clues about how to proceed. Banana trees need sun and moist soil. They also need a lot of water during the summer. The biggest threat is root rot during the winter. Aphids and moths can also attack the leaves. Despite their name, most of these cold-variety trees do not produce bananas, and even those that are produced are not edible. If you like the tropical look, they are a good bet for your yard.
Another popular tropical plant is the hardy palm tree. Some varieties are native to the southeastern United States. The needle palm, dwarf palmetto and windmill palm all tolerate DC’s climate and can be seen at the US Botanic Garden, National Arboretum and Smithsonian gardens.
In yet another category, many Hill gardens show off elephant ears and canna cultivars. This summer, the cannas seem to have popped up everywhere. “Canna musifiolia, canna ‘Pretoria’ and ‘Australia’ are three good varieties to choose from,” says Pyle.
Camellias are another popular and hardy tropical plant, native to China, Japan and Korea. A woody, evergreen shrub that can be pruned into a tree, the camellia thrives in partial sun and blooms in winter and early spring. Two camellias, C. japonica and sasanqua, have been bred by National Arboretum scientists and can be seen in the arboretum’s Asian Valley.
Lessons to Learn
If you like the exotic nature of these plants, adding them to your garden may be just the thing to do. But planting only tropical plants is not advised, as one cold spell could wipe out your entire garden.
A great resource for getting started is the “Palms Won’t Grow Here and Other Myths: Warm-Climate Plants for Cooler Areas,” written by David Francko. The book’s author chairs the department of botany at Miami University of Ohio. He is a firm believer that gardening is as much about personal outlook as about rules and techniques.
Pyle suggests visiting public gardens as another excellent way to research plants. “I like to go to Richmond, Norfolk and North Carolina gardens,” he says, “because it gives me a lot of ideas for new plantings. These gardens are within the possibility of zone bending in my own garden.”
So, with climate change affecting our community, now may be the time to experiment with tropical plants. Do your research. Check out Facebook groups on tropical plants. Visit public spaces. And plant as early as possible in spring. It is fine to grow in containers and bring indoors when young. Don’t cut things back in the fall; wait until they die to the ground.
Remember this rule: “When in doubt, don’t pull it out.” And, most of all, have fun.
Rindy O’Brien loves the idea of experimenting with plantings and looks for more varieties to come. Contact Rindy at email@example.com.