Mammillaria vetula subsp. gracilis (Pfeiff.) D. R. Hunt
Thimble Cactus, Thimble Mammillaria
Escobariopsis gracilis, Krainzia gracilis, Mammillaria fragilis, Mammillaria gracilis var. pulchella
Mammillaria vetula subsp. gracilis, also known as Mammillaria gracilis, is a small cactus with bright green cylindrical stems densely covered with white spines. It offsets freely to form large clumps. The stems are up to 5.2 inches (13 cm) long and 1.2 inches (3 cm) in diameter. They fall off easily but readily reroot. All spines are usually radial, but occasionally there are 1 to 5 dark-brown central spines. Flowers are creamy to pale yellow with pinkish or brownish mid-stripe and usually appear in spring but also in late summer and fall. They are up to 0.5 inches (1.3 cm) long and nearly equal in diameter.
USDA hardiness zones 9a to 11b: from 20 °F (−6.7 °C) to 50 °F (+10 °C).
How to Grow and Care
To encourage better flowering, allow the plants to enjoy a cooling period in the winter and suspend watering. Unlike many other cacti, which use their ribs as storage devices, Mammillaria feature raised tubercles, from which spines emerge. When you water, the tubercles will expand to allow for increased water storage. The flowers appear from these tubercles' axils on the previous year's growth, which accounts for their interesting halo effect. The cactus mustn't be exposed to prolonged dampness and sitting water. Never let your cactus sit in a dish of water. Lastly, make sure to fertilize during the growing season for the best results.
Repot as needed, preferably during the warm season. To repot Mammillaria, ensure the soil is dry before repotting, then gently remove the pot. Knock away the old soil from the roots, removing any rotted or dead roots. Treat any cuts with a fungicide. Place the plant in its new pot and backfill with potting soil, spreading the roots out as you repot. Leave the plant dry for a week or so, then begin to water lightly to reduce the risk of root rot.
See more at How to Grow and Care for Mammillaria.
This subspecies is native to Mexico (Hidalgo, Queretaro).
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