Dwarf evergreen shrub of the Ericaceae family, this cultivar is a hybrid derived from Rhododendron forrestii subsp. repens, a species native to Yunnan and Tibet, where it carpets rocky slopes and high-altitude screes by creeping along the ground. 'Scarlet Wonder' was developed in Germany and received the Award of Garden Merit from the RHS.
It forms a compact and spreading shrub, with a dense hemispherical habit, generally reaching 60 to 70 cm in height with a somewhat wider spread. The leaves are oval to elliptical, leathery, dark green and shiny on the upper side, lighter underneath, arranged in well-grouped terminal rosettes.
The flower buds are bright red as soon as they appear, particularly decorative several weeks before opening. The open flowers are funnel-shaped with wavy and slightly crumpled lobes, an intense and bright scarlet red, grouped in corymbs of five to eight flowers. Blooming occurs in April-May in cultivation.
This cultivar is distinguished by the combination of its very clean dark foliage, its early red buds, and its flowers with a chromatic intensity rarely matched in this size range. It requires acidic, humus-rich, fresh, and well-drained soil, sheltered from cold winds and in a semi-shaded to sunny exposure. Its hardiness is good.