Abstract

Twelve taxa of deciduous azalea were evaluated using laboratory procedures to determine hardiness of stems and flower buds. Rhododendron atlanticum, ‘My Mary’, ‘Nacoochee’, and ‘TNLV1’ exhibited the greatest stem cold hardiness, surviving to at least −29C ± 1 (−20F ± 2) in February 1996. Rhododendron oblongifolium exhibited the least stem cold hardiness, surviving to only −11C ± 1 (10F ± 2). All results were consistent with previous field studies. Except for R. viscosum and R. serrulatum, lowest survival temperatures for stems were analogous to reports available in the literature. Rhododendron viscosum and ‘My Mary’ had the lowest survival temperature recorded for flower buds, −23C ± 1 (−9F ± 2), in February 1998 and February 1999, respectively, though not significantly different than most other taxa examined. Lowest survival temperatures for flower buds varied from published accounts, with buds in the present study being less hardy than previously reported. Differences from published reports in the lowest survival temperatures of stems and flower buds are attributed to provenance, temperature fluctuations, cultural effects on the plants, and differences among freeze test protocols.