Isodon longitubus Tube Socks - Rabdosia

Isodon longitubus ‘Tube Socks’, still sold under the name Rabdosia longituba ‘Tube Socks’, is a tall partial shade perennial that really comes into its own at the end of the season. It forms a fairly insignificant clump during summer, then its stems bear fine, white, and very luminous flowers. Its elongated flowers are like small sage tubes, clearly visible in shaded spots. Plant white isodon at the foot of deciduous shrubs, at the edge of a border, or in a moist bed.

This variety belongs to the Lamiaceae family, which includes salvia, mint and plectranthus. The species Isodon longitubus grows naturally in southeastern China and central and southern Japan, particularly in mountain forests, at edges, and in damp sites under light canopy. Its main botanical synonyms are Plectranthus longitubus, Rabdosia longituba, Amethystanthus longitubus and Isodon longitubus f. albiflorus.

'Tube Socks' is a white form discovered in Japan, then introduced and named by American horticulturist Barry Yinger. It is a herbaceous deciduous perennial: its stems die back as soon as frost arrives, and the crown regrows fairly late in spring. The plant forms an erect clump 1 to 1.20m tall, sometimes more in rich soil. Its spread generally reaches 60 to 80cm. The thin, green to slightly purple stems are quadrangular, as with many Lamiaceae. The leaves are opposite, ovate to lanceolate, 7 to 15cm long, with a clearly toothed margin. Their light green colour can take on reddish tints at the end of summer. Flowering occurs in October and November. The flowers are tubular, white to creamy white, 2cm long, ending in two open lips. They are arranged in loose terminal clusters 20 to 30cm long. 

Position rabdosia 'Tube Socks' at the back of a slightly shaded bed, under deep-rooting deciduous trees, or in front of a hedge. Its flowering brightens dark foliage and pairs well with blue or purplish blooms. Pair it, for example, with Actaea simplex ‘Brunette’, Aconitum carmichaelii ‘Arendsii’  and Fuchsia magellanica ‘Hawkshead’.