Article Copied from the American Rhododendron Society Blog
Print date: 2/28/2024
3 July 2023 @ 17:40 | Posted by Joe Bruso
Have you ever taken the Blue Ridge Highway and watched a full scene of flaming color. It takes your breath away. You are seeing Rhododendron calendulaceum in its glory. It is one of the most spectacular native shrubs of the Appalachian Mountains. E.H. Wilson, the notable British plant collector and explorer, wrote, "..."It must be considered one of the most gorgeous of American shrubs." Why?
A little background surrounding this gem: calendulaceum means like a "calendula," a genus of flowering plants with similar flower color. It is one of 16 species in Rhododendron subgenus Pentanthera, section Pentanthera, referred to as the deciduous azaleas. it's commonly called the "Flame Azalea".
It was first identified in 1795 by Andre Michaux, a French botanist, in the Southeastern U.S. and since has played an important role in the early development of the Ghent Hybrids, which began with its cross with R. periclymenoides.
This gorgeous gem forms an upright, spreading shrub or small tree, which can grow from 4- to 15-ft. tall in the wild. but usually is much shorter in cultivation. Typical bloom time is May through June at which time you will find entire hillsides brilliantly colored. Its native habitat includes open, dry sites in woods, on cliffs and hillsides, and on bald open area on mountaintops from 600 to 5,000 ft. It is hardy to Zone 5 (-25°F or -30°C).
R. calendulaceum has close relatives! With the closest one being R. cumberlandense, a smaller plant with a paler flower. The scarcity of natural hybrids may be due to it being a tetraploid. whereas other azaleas in its range are diploid. Because of this genetic incompatibility, its hybrids are often sterile.
R. calendulaceum is difficult to propagate from cuttings, but it is very easy to grow from seed.