Espostoa melanostele aka Old Lady Cactus

Espostoa melanostele, or old man cactus, comes from Peru. It belongs to the cactus family, Cactaceae. Its range runs from southern Lambayeque to northern Ica. It grows on the west slopes of the Andes. There, it lives in dry scrub among thorny plants. Most sites lie at 2,625–4,920 feet [800–1,500 metres]. Some occur as low as 1,970 feet [600 metres]. Others reach 8,200 feet [2,500 metres].

This cactus forms upright stems and branches from the base. The RHS gives a garden 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]. Plants take about five to ten years to reach maturity. LLIFLE describes larger plants, most below 6.6 feet [2 metres]. Some reach 9.8 feet [3 metres]. New branches appear once stems reach 2.3–3 feet [0.7–0.9 metres]. Each grey-green stem can reach 0.33 feet [0.1 metre] across.

Dense white wool gives the stems their pale look. The hair cover grows thicker as the plant ages. Small growth points called areoles bear white or brown hairs. Sources give about 18–30 ribs along each stem. The spines start yellow, then turn almost black. Each areole bears many short radial spines and one to three central spines. The longest central spines reach 0.33 feet [0.1 metre]. A woolly flowering zone, called a cephalium, forms along one side. This zone may look white, yellow, or brown.

The white flowers have a bell shape. They measure 0.16–0.20 feet [0.05–0.06 metre] long. Their width reaches about 0.16 feet [0.05 metre]. The small fruits are about grape-sized. Their colours range from pale green-white to yellow-white or reddish. LLIFLE reports that the fruit is edible, with a sharp taste. The seeds are round, glossy, and dark brown to black.

Grow this cactus in full sun with shelter. Use cactus compost that drains well. It accepts sandy or loamy soil across a broad pH range. Give moderate water while it grows, then keep it nearly dry through winter. The RHS rates it H2: it tolerates cool conditions but not freezing. It suits a bright houseplant spot, conservatory, or greenhouse. It also suits patio pots where temperatures allow. Its woolly stems provide interest throughout the year. No pruning is needed. Raise new plants from seed or remove offsets in spring. Watch for mealybugs. Too much water can cause root and stem rot.