Myrtillocactus geometrizans aka Bilberry Cactus

Myrtillocactus geometrizans is a cactus native to Mexico. Gardeners call it blue candle or garambullo. It belongs to the cactus family, Cactaceae. It grows in dry scrub, forests that shed their leaves, and some grasslands. Wild plants grow at 3,281–6,562 feet [1,000–2,000 metres] above sea level. The species has a wide range and can be locally abundant. Useful Tropical Plants reports its conservation status as Least Concern.

This branching cactus forms a large shrub or small tree. Its upright stems make a dense shape like a candelabra. RHS gives a cultivated height of 1.6–3.3 feet [0.5–1 metre]. Its listed spread is 0.3–1.6 feet [0.1–0.5 metres]. Wild plants can reach 14.8 feet [4.5 metres] tall. Their crowns can span 16.4 feet [5 metres]. The stout stems look blue-green or blue-grey. Each stem has five to eight ribs with spaced areoles. These small pads bear clusters of dark spines. Older stem surfaces turn grey-brown and may become scaly.

Older plants bear small, funnel-shaped flowers along their stems. The flowers range from white to cream or greenish white. Sources place flowering from February through early summer. Chicago Botanic Garden lists March to April. LLIFLE reports that each flower lasts just one day. The small fruits turn dark red, purple, or blue-purple. Their flesh tastes sweet, with a flavour compared to kiwi. People eat both the fruits and flowers. They also dry the fruits for use like raisins. Mexican markets sell the fruits as garambullos.

Grow this cactus in full sun and well-drained cactus compost. RHS accepts sandy or loamy soil across a broad pH range. Under glass, it needs strong light and low humidity. Water moderately from mid-spring through early autumn. Keep it almost dry during the rest of the year. RHS recommends monthly low-nitrogen feed during that growing season. It lists UK hardiness as H1B, with summer outdoor use. Chicago Botanic Garden gives USDA zones 9–10. Seeds and stem cuttings provide ways to grow new plants.

Its bold form suits borders and planting as a specimen. RHS also lists it for homes, conservatories, and greenhouses. It attracts birds and butterflies, and deer tend to avoid it. Growers use it as rootstock for grafting other cacti. People also use its wood and burn it as fuel. It needs no pruning and has few reported disease problems. Mealybugs may attack it. Useful Tropical Plants lists no known hazards; this does not establish pet safety.