Big-flowered rhododendrons rank among the world’s most beautiful shrubs. Huge trusses of blossoms in a wide range of colors stand atop large, leathery leaves in spring and summer. Gardeners in northern California, the Pacific Northwest, and the Northeast can grow them as easy as mildew in a shower. But here in the South, you can’t take them for granted. You can only take a chance.
The reason is that rhododendrons, especially the spectacular hybrids, don’t like the climate and heavy soil that besets most of the South. It’s too hot for too long; it doesn’t rain, it pours; summer nights are sultry; and clay soil that gets wet takes forever to drain.
You begin to understand when you visit the one place in the South where native Catawba and rosebay rhododendrons ( Rhododendron catawbiense and maximum ) thrive, forming thickets as tall as 30 feet – the Blue Ridge and Appalachian Mountains. Summer temperatures there are typically 10-15 degrees cooler than those down below. Summer nights drop into the 50’s. Frequent fog caresses the foliage with gentle moisture. Rocky soil containing lots of organic matter drains quickly.
Most hybrid rhododendrons recommended for the South contain R. catawbiense blood, like ‘Album Elegans,’ ‘Anna Rose Whitney,’ ‘Caroline,’ ‘English Roseum’ (shown above), and ‘Roseum Elegans.’ They tolerate more heat than others, but that’s far from a long-term guarantee. Take a look at this photo of ‘Caroline’ I took in my garden yesterday. It’s been there for 12 years. It has flower buds. And it’s going to die.
and soon will turn brown. And there’s nothing I can do about it.
My doomed plant has been attacked by one of two diseases – rhododendron dieback or rhododendron root rot. It doesn’t matter which. The symptoms are quite similar and produce the same results. Both fungi live in the soil and enter the plant through the roots or cracks in the bark near the soil line. Once they’re inside, chemical treatments are useless. A vigorous plant may fight them off and lose only a few branches, which you should cut back to healthy wood. A stressed plant will likely die.
Why is my plant stressed? Well, this has been a very wet July and August in central Alabama featuring nearly daily downpours. Rhododendrons don’t like high heat and wet soil. No siree.