Browningia hertlingiana aka Blue Cactus

Browningia hertlingiana is a tall cactus from Peru. It belongs to the cactus family, Cactaceae. Gardeners also call it blue cereus or blue cactus. Older names include Azureocereus hertlingianus and Clistanthocereus hertlingianus. It grows on dry slopes between Andean valleys. Records place it in Ayacucho, Apurímac, and Huancavelica. Its habitat lies at 3,280–9,840 feet [1,000–3,000 metres]. Farming has reduced some groups, while steep slopes offer protection.

This long-lived succulent takes a tree-like form with upright stems. Under good conditions, it can reach 26 feet [8 metres]. Its full spread can reach 13 feet [4 metres]. These are eventual sizes, not a stated garden range. Several stems rise from a trunk about 3.3 feet [1 metre] tall. The stems can reach 1 foot [0.3 metres] across. They branch little above the trunk. Young growth has a blue coating; older stems turn pale olive. Warmth and strong light help the blue colour develop.

Raised bumps line the ribs, with slightly sunken areoles at their tips. Young stems bear stiff, uneven spines with brown tips. These range from yellow to grey-yellow. The longest reach about 0.26 feet [0.08 metres]. Flowering stems bear more spines, which are finer and more flexible. White flowers open at night during summer. Chicago Botanic Garden lists bloom time as July to August. Flowers reach about 0.16 feet [0.05 metres] across. Their curved tubes and buds have deep purple-brown tones. Plants must exceed 3.3 feet [1 metre] before flowering. The dry fruits measure about 0.08 feet [0.025 metres] across.

Grow this cactus in full sun with soil that drains well. Let the soil dry between waterings. Growth is slow, with active growth in summer. Low-nitrogen feed in spring and summer can speed growth. Chicago Botanic Garden lists USDA zones 9–11. LLIFLE reports brief frost tolerance near 23°F when dry. It recommends keeping cultivated plants above 41°F. Cool, damp winter conditions can cause rot. Keep the winter rest dry and avoid high humidity.

Collectors grow this species for its blue stems and gold-toned spines. Chicago Botanic Garden lists it for beds and borders. It also records bird and butterfly interest, plus deer resistance. Seed is the main means of propagation. The supplied sources do not establish food uses or toxicity.