The American Horticultural Society developed a heat zone map similar to the USDA cold hardiness map. While heat hardiness using these heat zones is beginning to be published for specific plants, just as for cold hardiness zones, the heat zone information is not yet as readily available. Many deciduous hybrid azaleas appear to be more sensitive to high temperatures than evergreen hybrids. Hybridizers are working to improve the heat tolerance of deciduous hybrids by crossing them with the very heat-tolerant native R. austrinum . You can help achieve this by removing the lower limbs from the existing trees, at least as high up as you can reach with a pole saw.
Azaleas can also adapt to extremes.
Many varieties, particularly deciduous azaleas, can handle more sun if they are given enough water. In general, azaleas grown in full sun will have shorter stems, and may have more blooms which will not last as long, and which may fade in a few days. In full shade, many varieties will grow longer stems as they reach for the light, and they may not produce as many blooms, but the blooms will last longer. In the south, fewer azaleas can thrive in full sun than in the north. Similarly, fewer azaleas, and particularly deciduous azaleas, can thrive in full shade in the north than in the south.