Mammillaria spinosissima Lem.
Red-headed Irishman, Irish Red-head
Mammillaria spinosissima subsp. spinosissima, Mammillaria auricoma, Mammillaria pitcayensis, Mammillaria pilcayensis, Mammillaria centraliplumosa, Mammillaria haasii, Mammillaria gasterantha, Mammillaria crassior, Mammillaria virginis
Mammillaria spinosissima is a cactus with a cylindrical, dark blue-green stem almost hidden under a dense covering of spines. The stem grows up to 12 inches (30 cm) tall and up to 4 inches (10 cm) in diameter. Flowers are freely produced in spring and form a ring around the upper part of the plant. They are purplish or deep-pink, up to 0.8 inches (2 cm) long and up to 0.6 inches (1.5 cm) 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, make sure the soil is dry before repotting, then gently remove the pot. Knock away the old soil from the roots, making sure to remove any rotted or dead roots in the process. 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.
Mammillaria spinosissima is endemic to Mexico.
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