Rhododendron ‘Minnetonka’ (Rhododendron ponticum x unknown) – One of the modern Ironclad hybrids which was bred specifically for hardiness. ‘Minnetonka’ bears reddish-purple blooms (from May to June) that fade to a light purple, with an eye-catching yellowish-green blotch. A good choice for commercial sites. Grows 3-4′ high and wide. Hardy to zone 5.
Rhododendron ‘Anah Kruschke’ (R. ponticum seedling x Rhododendron catawbiense) – Bred by Franz Kruschke of Oregon back in 1948 (and named for his wife), ‘Anah Kruschke’ is considered by many to be a modern Ironclad due to its sun and heat tolerance. Bears reddish-purple blooms over deep green foliage. Grows 5-6′ high by 4-5′ wide. Hardy to zone 5.
Rhododendron ‘Lavender Queen’ (R. catawbiense ‘red’ seedling x ‘Boule de Neige’) – Another favourite rhododendron bred by Shammarello in 1970. It features pale bluish-lavender blooms with distinct wavy or frilled flower petals. These are borne from May to June over deep green foliage that may bronze in winter. Grows 4-5′ high by 5-6′ wide. Hardy to zone 6.
Rhododendron ‘Polarnacht’ (‘Turkana’ x ‘Purple Splendour’) – With a name that translates as ‘Polar Night’ you can expect something special. The very dark purple blooms are held in tight trusses and contrasted by deep red spotting and ghostly white stamens. This German hybrid was bred by Hachmann and is a must for purple lovers. Grows 3-4′ high by 4-6′ wide. Zone 5.
Rhododendron ‘Blue Pacific’ (‘Purple Splendour’ x ‘Susan’) – Bred by Whitney in 1962, this beautiful hybrid lives up to its name with bluish-purple flowers (with a darker blotch) held in ball-shaped trusses of 10 to 16 blooms from May to June. It has large mid green foliage and seems to prefer a partial shade exposure. Grows 5 feet high by 4 to 6 feet wide. Hardy to zone 6.