Given strong preferences for cool, moist growing conditions, it's not surprising that "rhodies"--as they're affectionately known--are sulking. Extensive but shallow root systems adapt them to the rich, well-drained soils common along riverbanks. Overhead shade and plenty of moisture in their favored environments keep them cool, content and healthy.
Vigorous stands of our native rosebay rhododendron (Rhododendron maximum) are still found along many of Pennsylvania's scenic streams.
Yet outside of this rather narrow "comfort zone," the roots appear to be struggling. Shade helps some, but higher ambient air temperatures in summer are simply beyond our control. Lack of rainfall and snow cover is a real problem for them.
As a result, new landscape plantings of rhododendrons and azaleas often fail to thrive and many gardeners have lost large old established plants to the elements. Even the "ironclads" like 'Roseum Elegans' and 'English Roseum' are declining in this region.
I hardly ever recommend the rosebay anymore, unless it can be nestled in a woodland setting or the gardener is fortunate enough to have a stream running through his or her property.
As so often happens in nature, predators conspire to take advantage of the weak. The "predators" in this case are insects and diseases. And where rhododendrons and azaleas are stressed, some nasty predators are moving in for the kill.
The Rhododendron borer represents Mother Nature at her cruelest. From specimens already weakened by drought, adult borers select their victims. The larvae "mine" the lower stems, leaving behind ravaged plants that frequently die.
If the borer doesn't find them first, fungus diseases such as Phytophthora blight and leaf spot get a turn at the twigs and foliage. Scale insects, azalea lacebug, leaf curl, caterpillars and black vine weevils scavenge what's left.
None of these plagues--except leaf curl, which is directly attributable to drought--is new. But Rhododendron borers and Phytophthora, which were scarcer just a decade ago, seem to be everywhere now.
Some horticulturists are blaming these pests for the decline of rhododendron and azalea populations in the Northeast. I think that reasoning is backward.
To those of us who love them, gardening without rhododendrons and azaleas is unthinkable. Be we have to plant smarter and choose varieties that can adapt to current climatic conditions.
Members of the American Rhododendron Association (ARS) especially like the variety called 'Janet Blair' for gardens in my region (USDA Zone 5b). The lovely pale-pink-to-white blooms, with green brush marks and "freckles" on the lower petals, are also favorites of mine; I'm pleased she's so resilient. Plants are sturdy and compact, with very deep-evergreen foliage.
The "Yaks" (Rhododendron degronianum subsp. Yakushimanum) are also still performing well here, especially the robust 'Ken Janek', the blushing 'Mist Maiden' and the delicate 'Yaku Angel'. Yak rhododendrons are small plants, just 4 feet high at maturity, but this suits many gardens better than species that grow to enormous proportions. For their tough constitution and excellent winter foliage color, the nod goes to plants from the PJM hybrids, a group of about 50 distinct and unusually hardy plants.
To find varieties the ARS recommends for your region, visit their Web site at www.rhododendron.org.
So closely related to rhododendrons that they share the same genus (Rhododendron ), azaleas are experiencing many of the same challenges. Evergreen azaleas seem to be suffering more than the deciduous types, with scale and lacebug emerging as primary opponents.
Fortunately, deciduous azaleas are easy to love. Start with any of the Northern Lights series, new from the breeding program at the University of Minnesota--read "hardiness plus." My personal favorite is 'Northern Highlights'. Pure-white blossoms with golden throats cover the plants in spring with their spectacular trusses.
Do your best to keep existing rhododendrons and azaleas healthy by supplementing with plenty of water during dry spells. Beneath an organic mulch of compost or shredded bark, the roots will stay cool and damp. Provide the shade they love if you can.
(Lindsay Bond Totten, a horticulturist, writes about gardening for Scripps Howard News Service.)
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