QBARS - v28n1 Rhododendron caloxanthum

Rhododendron caloxanthum, Exbury form
Meldon Kraxberger, Portland, Oregon

R. caloxanthum
R. caloxanthum
Photo by Stanley Anderson

Many rhododendron collectors find their favorite plants in the Thomsonii Series - there are so many "once seen never forgotten' plants in this group. Rhododendron caloxanthum belongs to this aristocratic class, and the Exbury form is the one to grow. Seedlings are not blessed with this intense yellow. Closely related to Rhododendron wardii , it is a smaller plant, well-foliaged with rounded green leaves, pale beneath, and April bloom. The waxy-belled corollas only number about five in a lax truss but a two-foot caloxanthum wears a golden mantilla. The lovely sunny buds are tipped with orange and, as the orange fades away, the yellow intensifies. There is a small crimson basal stain deep in the bell.
This is definitely a yellow rhododendron, not just classed as yellow as is R. 'Unique'. Half-shade, good drainage and attention with water during hot dry summer weather are necessary, as with all of this series. The Exbury form roots without resentment and grows slowly during the first few years. It is definitely worth the wait. The plant pictured, much larger now, bloomed well last spring after the devastating freeze of December, 1972. R. caloxanthum is classed as H3 (-15° F) and decorated with three stars. Perhaps one day soon some hybridist, smitten with yellow fever, will produce from this lovely plant a truly yellow R. 'Unique', and wouldn't that be great?