Mammillaria senilis

Mammillaria senilis is a small cactus from northern Mexico. Its range runs south to Nayarit. It belongs to the cactus family, Cactaceae. Sources place it in Chihuahua, Jalisco, and Sinaloa. It grows on mossy rocks in high pine woods. These sites lie at 7,874–9,186 feet [2,400–2,800 metres]. Kew also lists desert or dry shrubland as its habitats.

White wool and dense white spines cover the stems. Plants often grow alone. Shoots from the base can also form clumps. The stems start round and may grow into upright cylinders. Most accounts give a height of about 0.5 feet [0.15 metres]. The RHS gives a wider range, up to 1.6 feet [0.5 metres]. Its listed spread reaches 0.33 feet [0.1 metres]. Blunt, cone-shaped bumps, called tubercles, have wool and bristles between them. Each spine group has many fine spines on the outside. Fewer stout spines grow in the centre. Some of these have hooked ends and yellow tips.

The large flowers stand out against the pale stem cover. Most are orange-red. LLIFLE also notes other colours. Long tubes give the flowers a trumpet shape. Flowers reach about 0.2 feet [0.06 metres] long, sometimes a little more. The RHS lists blooms from spring through summer. LLIFLE gives a shorter span: February and March. Fruit ranges from silver-red to greenish white. It holds black seeds.

Give this slow-growing cactus strong light and shade from harsh sun. Use cactus compost that drains well. Its pH should be acidic to neutral. Water in the growing season, then let the mix dry. Cut back water sharply in winter. Keep air flowing well around the plant. Wet roots can rot, so do not keep the compost soaked. The RHS advises a balanced liquid feed once a month. Give this from mid-spring to late summer. Its RHS rating is H2. Cool sites suit it, but it cannot take freezing.

Its small size suits pots and bright spots indoors. It also suits growing spaces with shelter. The RHS suggests patios, greenhouses, and conservatories. Plants may take five to ten years to mature. They need no pruning. Sow seed in late winter or early spring. Or, detach offsets in early spring. Check stems and roots for mealybugs. The RHS reports few disease problems. LLIFLE stresses care with watering. The hooked spines are sharp, so handle the plant with care.