Leuchtenbergia principis Hook.
Agave Cactus, Cob Cactus, Prism Cactus
Leuchtenbergia principis is a unique cactus with a cylindrical stem and long grayish-green tubercles with purplish-red blotches at the tips and topped with papery spines, which makes it resemble an Agave. It slowly grows up to 28 inches (70 cm) tall. The stem becomes bare and corky at the base with age. Tubercles are triangular in cross-section and up to 3 inches (12.5 cm) long. After four years or so, yellow flowers appear at the tip of the tubercles from spring to fall. The flowers are funnel-shaped and up to 2.4 inches (6 cm) in diameter. Fruits are smooth, green, up to 1.2 inches (3 cm) long, and 0.8 inches (2 cm) in diameter.
L. principis is the only species of the genus.
USDA hardiness zones 9a to 11b: from 20 °F (−6.7 °C) to 50 °F (+10 °C).
How to Grow and Care
Agave Cactus is reasonably easy and tolerant and should grow well, given the basic guidelines for growing cacti and other succulents. However, this desert species adapted to arid conditions seem to benefit from intense solar radiation. Therefore, it should always be moved to a position outside during the warmer months of spring through early fall to benefit from exposure to direct sunlight and summer's increased temperatures.
Grown exclusively indoors, this species will slowly languish from the comparatively low light levels of interior spaces and probably never really thrive. However, grown outdoors, this plant has proven to be a reliable bloomer, invariably producing intermittent blooms from spring to fall.
Agave Cactus tolerate a remarkable amount of rain through their outdoor growing season despite its desert origins. Still, their large, turnip-like roots can be very susceptible to root rot when exposed to extended cold and wet conditions. So, the potting medium should be especially gritty to provide that extra drainage necessary for this species. Also, extra care should be given through winter to prevent overwatering this species. Many growers do not water this plant at all in the winter.
Agave Cactus is usually propagated by seeds, as it rarely pups or produces offsets. It has been reported that plants can be propagated by tubercle cuttings, but this method is not common.
This species is native to north-central Mexico (San Luis Potosi, Chihuahua).
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