Eranthemum pulchellum aka Blue Sage

Eranthemum pulchellum is a tropical evergreen shrub called blue sage. It belongs to the acanthus family, Acanthaceae. Its native range includes India, the Himalayas and western China. Chicago Botanic Garden also lists Nepal within its range. The names Daedalacanthus nervosus and Eranthemum nervosum are synonyms. This shrub keeps its leaves through the year. Its upright branches form a loose, open shape.

Garden plants reach about 2–5 feet [0.6–1.52 metres] tall. They can spread to about 4 feet [1.22 metres]. RHS gives a smaller height and spread, both to 3.3 feet [1 metre]. Plants take five to ten years to reach full size. The green leaves have a glossy surface. Their shape ranges from oval to narrow and pointed. Leaves can reach 4–8 inches [10–20 centimetres] long. Tall stems may become leggy and need cutting back.

Deep blue flowers grow in spikes at shoot tips and leaf joints. These spikes reach 3–6 inches [8–15 centimetres] long. Each bloom measures about three-quarters of an inch [2 centimetres] across. Green bracts with white veins sit beneath the flower spikes. They stay on the plant after the flowers fall. The main flush comes in late winter and early spring. In warm sites, flowers may last through much of the year. Cutting back leggy growth can prompt a fresh flush of blooms.

Grow this shrub in rich soil that drains well. Keep the soil moist without leaving it waterlogged. It grows in sun or partial shade, with protection from hot afternoon sun. Under glass, RHS advises bright, filtered light in loam-based compost. Water moderately during growth and give less water in winter. Apply a balanced liquid feed each month during growth. RHS accepts acid, neutral and alkaline soils. Missouri Botanical Garden places outdoor winter hardiness in USDA zones 10–11. RHS rates it H1B, suited to summer outdoors in Britain.

Use blue sage in groups, bedding or near border fronts. It also works as a single specimen or container plant. In cold regions, keep it in a greenhouse or overwinter containers indoors. Plants under glass may need pruning to limit their size. Root softwood cuttings with bottom heat in late spring or early summer. Serious pest and disease problems are uncommon. Watch for whitefly, scale, mealybugs, mites and nematodes.