Want more tropicals in your Nashville garden?
Hardiness Zones, Heat Zones and Microclimates Create More Options
Although you wouldn’t know it from the brutal cold this winter, Greater Nashville is officially in a warmer hardiness zone than it was four years ago.
In January 2012 the USDA updated its plant hardiness map, the first such update in 12 years. Nashville itself had been in Zone 6B; now it is in Zone 7A. The shift, though slight, increased our average annual extreme minimum temperature from -5 to 0 degrees to 0 to 5 degrees (F).
For gardeners, however, those five little degrees make a big psychological difference because Zone 7 is the outside limit for semi-tropical perennials. Perfect World Landscaping is not advising you to rush out and pepper your landscape with plants rated for Zones 8 through 10. That said, the warming trend is good news if you want to add more tropicals to container gardens.
Burgundy Cordyline, with its striking spiked foliage, is a popular option, as are the newer black and gold cannas. A staple of California’s Bay
Area landscaping – Agapanthus africanus, with balls of blue or white flowers on tall stems – also may work in protected containers.
Experiment with microclimates
Microclimates give gardeners more options and a better shot at success when experimenting with tropical plants. A south-facing brick wall, for example, absorbs heat in the day and radiates it back into the environment at night, creating warmer air near it. Fences and large rocks or boulders produce a similar effect.
Filled with buildings and paved surfaces, urban areas usually will have less extreme low temperatures than rural areas only a few miles down the road. A protected courtyard in Belle Meade will not get as cold as a backyard in rural areas of Antioch or Pegram.
Wind protection is another factor, so understanding the direction of your prevailing winds and how they wrap around your home can make for wiser plant choices.
Remember, too, that warmer microclimates in the winter will also be warmer in the summer, which means plants need frequent watering and may scorch if they can’t stand the extra heat.
Not all microclimates are warmer. Because cold air falls and settles, dips and valleys will be colder (and often wetter). Wind affects the tops of hills more intensely, which can create conditions that are both drier and colder.
AHS Heat Zone is another measure
The American Horticulture Society “Heat Zone” map focuses on the other extreme. The 12-zone map uses 86F or higher as the demarcation for temperatures that damage common plants. The higher the zone number, the more days at 86F or above, so Zone 1 is one day or less and Zone 12 is 210 or more days each year that reach 86F or higher.
Most of Greater Nashville is in Heat Zone 7, meaning 60 to 90 days a year at 86F or above.
Remember, both the USDA and AHS maps are guides. What plants thrive where has much to do with topography, nearby structures, expanses of concrete or adjacent large bodies of water. Perfect World Landscaping would be delighted to guide you in choosing the right trees, shrubs, perennials and groundcovers. We can talk about plants all day.