Crepe myrtles (Lagerstroemia indica) are prized for their long summer blooming season and attractive, exfoliating bark. These trees thrive in warm climates, reliably producing vibrant pink, red, purple, or white flowers. Successful cultivation hinges on the geographical location and the plant’s ability to survive winter temperatures. Understanding the temperature tolerances of this species is necessary before selecting a variety to plant in your landscape.
Understanding the Hardiness Zone System
The recognized standard for determining a plant’s cold tolerance is the USDA Plant Hardiness Zone Map. This map divides the United States into 13 zones based on the average annual extreme minimum temperature for a given region. Each zone represents a 10-degree Fahrenheit range, indicating the coldest temperature a plant can be expected to endure in that area.
Gardeners use this system to determine which perennial plants, trees, and shrubs are most likely to survive the winter and thrive in their location. Each main zone is further divided into two subsections, labeled ‘a’ and ‘b,’ which represent a tighter five-degree Fahrenheit temperature range.
The Ideal Hardiness Zone for Crepe Myrtles
Traditional crepe myrtles are best suited for USDA Hardiness Zones 7 through 10, where they can grow as full-sized trees or shrubs. Zone 7, with minimum temperatures ranging from 0°F to 10°F, is the general threshold for survival. In this range, the plant is reliably “root-hardy” (the underground structure survives) and often “top-hardy” (above-ground branches remain alive). Zones 8 and 9 allow the trees to reach their full mature size and exhibit the best growth with minimal cold damage. However, in the cooler limits of Zone 7, harsh winters can cause branches to die back to the ground, resulting in the plant acting more like a perennial shrub.
Cultivars and Cold Tolerance
Plant breeders have developed specific cultivars that push the boundaries of crepe myrtle hardiness. These newer varieties often result from hybridizing Lagerstroemia indica with the cold-tolerant Japanese crepe myrtle, Lagerstroemia fauriei. Certain cold-tolerant selections, including ‘Dynamite,’ ‘Tuscarora,’ and ‘Sioux,’ are reliably hardy into USDA Zone 6, where minimum temperatures drop to -10°F. In Zone 6, these varieties are generally only root-hardy; the stems and branches will likely freeze and die back each winter. The plant regenerates from the roots in the spring, blooming on new growth, but remains a smaller shrub rather than developing into a large tree.
Extending the Growing Range
For gardeners in marginal areas, like the colder parts of Zone 6 or even Zone 5, strategic planting and physical protection can help extend the growing range. Selecting a sheltered microclimate, such as a location near a south-facing brick wall or foundation, can provide extra warmth. This placement helps mitigate the harshest effects of cold wind and sun scald. Applying a thick layer of mulch over the root zone in late fall is crucial for insulating the crown of the plant from deep freezing. Alternatively, smaller or dwarf crepe myrtle varieties can be grown in large containers and moved into a protected, unheated space, such as a garage or shed, during the winter to prevent the roots from freezing solid.