Iron-Clad Rhododendrons

R. catawbiense was collected in the wild in 1803 in the Eastern U.S. and was introduced to Britain in 1809. When hybridized with other rhododendrons it introduced cold and heat hardiness into rhododendron hybrids. The first group of rhododendrons to become popular in gardens was the hybrids called the "iron-clads." There were a group of early British hybrids involving crosses of R. caucasicum, R. catawbiense, R. ponticum and R. maximum that survived the coldest winters at Arnold Arboretum in Boston. In 1917, Ernest Henry Wilson (1876-1930) published a list of what he termed the "Iron Clad" rhododendrons that for many years were successfully growing in the Arnold Arboretum.

 Wilson's Dozen Iron-Clad Rhododendrons

 1. Album Elegans, pale purplish pink hybrid or selection.
 2. Album Grandiflorum, pinkish white hybrid or selection.
 3. Atrosanguineum, bright red with purple markings hybrid.
 4. Catawbiense Album, pinkish white hybrid or selection.
 5. Charles Dickens, crimson red with purplish markings hybrid.
 6. Everestianum, purplish-pink with green markings hybrid.
 7. Henrietta Sargent, a deep pink hybrid.
 8. Lady Armstrong, deep purplish pink, pale center hybrid.
 9. Mrs. Charles S. Sargent, rose pink hybrid.
10. Purpureum Elegans, pinkish purple hybrid.
11. Purpureum Grandiflorum, violet with green flecks hybrid.
12. Roseum Elegans, lavender pink with green markings hybrid.