Discocactus horstii Buining & Brederoo
Discocactus horstii is a small cactus with a spherical, usually solitary stem segmented by 12 to 22 prominent ribs. It grows up to 2 inches (5 cm) tall and has a flat cephalium that grows up to 2.4 inches (6 cm) in diameter. The stem is green, turning dark red or brown as it ages. In summer, it produces spectacular white flowers. They are nocturnal, fragrant, up to 3 inches (7.5 cm) long, and up to 2.4 inches (6 cm) in diameter. Fruits are white and contain black seeds.
USDA hardiness zone 10a to 11b: from 30 °F (−1.1 °C) to 50 °F (+10 °C).
How to Grow and Care
Discocactus is probably one of the most difficult cacti to keep growing on its own roots and is almost always seen as a grafted plant. If growing on its own roots is attempted, the soil must be extremely free-draining, and watering should only take place after the compost has dried out and then only on sunny and warm days.
Discocactus are tropical species and should be kept warm in winter. The grafted plants are less cold-sensitive, but none has any frost tolerance. Mature Discocactus stop growing and instead divert their energy into developing a cephalium. The cephalium is a specialized flowering head, generally covered with fibers.
Discocactus will take full sun but prefers a little shade in the afternoon. Water with extreme care after the compost has dried out. See more at How to Grow and Care for Discocactus.
Native to Minas Gerais, Brazil, at an altitude of about 3280 feet (1000 m).
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