Isodon effusus

Isodon effusus, or Plectranthus effusus, is part of a group of perennials from Asia that thrive in partial shade and are appreciated for their delicate late flowering. This effusa species, quite rare in cultivation, is a favourite among connoisseurs. It is a delicate plant with a beautiful fountain-like habit, which produces light panicles adorned with tiny bright blue-violet flowers in October. Resistant to cold, this rather accommodating plant prefers slightly sheltered exposures as well as humus-rich soils that remain moist even in summer, where it will fully thrive.

Isodon effusus is a deciduous perennial belonging to the Lamiaceae family, just like salvias. It is native to mountainous areas of Japan, where it is found on forest edges. Resembling a plectranthus, it forms a tuft with a flexible, spreading habit, composed of outwardly arching leafy stems. Its growth is quite slow. When mature, it will reach approximately 70cm (28in) in height and 50cm (20in) in width at the base. Emerging from the ground in spring, its sturdy stems bear opposite, narrowly triangular and elongated leaves with a long pointed tip, toothed edges, and a fairly light green colour. The small tubular flowers appear in October and continue to bloom on the plant as long as it doesn't freeze. They are carried in sparse panicles. The stems die back each year in winter and new growth starts rather late, from April onwards.

It is perfectly hardy and able to withstand temperatures of around -16°C (3.2°F). It is undemanding in terms of soil composition. Isodon effusus thrives in partially shaded positions, protected from the sun during the hottest hours of the day. These conditions can be met on the edge of a grove, in front of deep-rooted deciduous trees or shrubs that won't use up all the available nutrients at the soil surface but will protect the flowering from cold winds. Isodon also enjoys being near a north or east-facing wall, in the company of hydrangeas, Japanese anemones, Fuchsia magellanica 'Alba', corydalis, strobilanthes, aconites, and foxgloves. Bulbs of Naples cyclamen can be planted at its base. Pairing it with purple foliage plants in autumn, such as physocarpus, hydrangea Endless Summer® 'Twist and Shout', or the dentate viburnum is simply stunning. Ferns make perfect companions.