The unusually cold weather we have been having in the north eastern United States has got us wondering about hardiness. Sweetbay has a paticular fondness for Lagerstroemia indica (the common Crapemyrtle) and we have the plant on a number of our projects on Long Island. As many readers will know, the plant does great south of the Mason-Dixon line but can bet temperamental in zones 6 and 7.
We have a great deal of success with the plant even though it is on the edge of it's hardiness zone. Michael Dirr, in his Manual of Woody Landscape PLants, writes that the ability of a plant to acclimate and deacclimate to cold weather is possibly more important to it's survival than low temperature tolerance. While Dirr does point out that Lagerstroemia is very sensitive to late spring and early fall freezes, we have found that, properly sited, the hazards can be mitigated. As he points out later in his book, a plant's hardiness is not an absolute value and living things are often more resolute than we expect.