Lycianthes rantonnetii aka Blue Potatobush

Lycianthes rantonnetii is an evergreen shrub called blue potato bush. It belongs to the nightshade family, Solanaceae. The older name Solanum rantonnetii remains a synonym. Kew records its native range from Bolivia to southeastern and southern Brazil and northeastern Argentina. The RHS also lists Paraguay within its range. This is a plant of subtropical regions. It is not native to Britain or Ireland.

Its loose, bushy growth needs support when grown in gardens. Mature plants reach about 5–8 feet [1.5–2.5 metres] tall and wide. The RHS gives two to five years for reaching maturity. Its evergreen foliage provides cover beyond the flowering season. Clusters of purple-blue flowers appear in summer and autumn. Each flower has a funnel shape and a light scent. Red berries follow the blooms. These fruits add another season of interest, but they are not food. All parts can cause severe discomfort when eaten.

Grow it in moist loam that drains well. It accepts acid, neutral, or alkaline soil. Outdoors, choose full sun and shelter from harsh exposure. A south-facing or west-facing site suits its needs. The RHS rates its hardiness as H3. This places it in the milder and coastal parts of Britain. Its listed winter temperature band is 23–34°F [-5 to 1°C]. In very mild sites, it may survive against a wall. Elsewhere, it needs cover during winter rather than an exposed garden site.

A pot-grown plant can be trained as a standard. Move the pot under cover for the winter months. A cool greenhouse or conservatory offers another way to grow it. Under glass, give shade from the strongest sun and moderate humidity. Its flowers suit courtyards, patios, and borders beside walls. The RHS also lists it for gardens in Mediterranean climates. Match pruning to its form, whether freestanding or trained against a wall.

Under glass, watch for aphids and glasshouse red spider mites. Grey mould can also affect plants grown under cover. Raise new plants from seed or from semi-ripe cuttings. Take these cuttings in summer or early autumn. Gentle heat beneath the cuttings helps them root. Wear gloves when handling the plant, then wash your hands. Keep its toxicity in mind when choosing a planting site.