Plant of the Week: Catawba Rhododendron (Rhododendron catawbiense)

The past few weeks I have been hiking around the forests of eastern Kentucky continuing the work on my waterfall book and invariably I come across large patches of rhododendron.  While most of the rhododendron in Kentucky is rosebay (R. maximum), which has white to pink flowers and blooms in June, we do have populations of the catawba rhododendron which has the pink to purple flowers which open in mid-May and primarily occurs in the true mountains of southeastern Kentucky.  So I figured now was a good time to talk about green in the winter garden that can be provided by rhododendrons.  I will group the two species together because they both have similar growing conditions in the garden.  Also, a big disclaimer here.  Do not ever eat rhododendron leaves as they will kill you very quickly.  It is one of the most toxic plants in nature.  In fact, the honey made from rhododendron flowers is also toxic and a few years ago some small children in Korea died from eating honey made from azaela flowers.  Because this is such a showy plant, the catawba rhododendron has a large number of cultivars and hybrids that are for sale.  Those recommended by the Department of Horticulture at UK include: America, Crimson Glory, Cunningham's White, English Roseum, Janet Blair, Lee's Dark Purple, Maxicat, Nova Zembla, Roseum Elegans, and Scintillation. The recommended cultivar for rosebay is Album.  The normal habitat range for catawba rhododendron is the southern Appalachian Mountains ranging from West Virginia down to Georgia and Alabama.  The rosebay has a similar but much larger range occuring all the way up to Maine.  This is a fairly easy plant to grow and is commonly found around homes, often as a foundation plant.  It requires light morning shade and moist, well drained soil.  In Kentucky, you typically find catawba growing near rock outcroppings but I have seen it growing in good, moist forest soils as well.  The rosebay requires similar habitat and it is quite common thoughout eastern Kentucky.  While in nature it appears to like the acidic soils, it does okay in the limestone soils as long as it is well drained and doesn't get too much sun and is protected from the wind.  It should also be given a good dose to sulfur and acid type fertilizer every year.  It has been described as slow growing but I had a rosebay in my yard that grew 6' tall in 3 years and flowered and it started as a 6" tall pip.  The plant can grow 6 to 8' tall and rosebay can get even taller than that.  The cultivars are much more compact growing than the wild species.  When temperatures drop in the winter, the large 6 to 8" leathery leaves have a tendency to droop and curl but it should be protected from the wind. You can encourage more prolific blooming by deadheading the flowers from the preceeding year.  This plant is susceptible to chlorosis in limestone soils and it should never be planted where it can get too hot and windy.  It definitely likes the well drained acidic soils and to encourage flowering it should be given a dose of fertilizer annually.  The two primary problems with the plants are root rot and black vine weevil.  One final note, if you are looking for the true wild species be careful of the various cultivars as many of them are undoubtedly hybrids.