Despite its common name, this Mexican native isn't a palm, but a relative of yucca and agave. Lush, pendulous, bright green leaves sprout from a woody trunk held above a greatly swollen base that the plant uses to store water. Young plants resemble big onions sitting atop the soil (with just a bit of the base below ground); older ones can reach 15 feet tall and about half as wide, with leaves to 3 feet or longer. Very old plants may develop several branching trunks and produce large clusters of tiny, creamy white flowers in summer.
Ponytail palms won't tolerate extended cold, so they're indoor plants outside of central and south Florida. Indoors, they need at least 4 hours of sun per day; a south- or west-facing window is a good spot. Make sure the soil is fast draining, and let it go dry between thorough soakings. Overwatering results in soft spots on the plant's base. Feed with a general-purpose liquid houseplant fertilizer every other week in spring and summer, once a month in fall and winter. Use horticultural oil or insecticidal soap to control scale insects and mealybugs (take plants outdoors to spray them). Prune the woody stem just above a leaf to encourage branching. When repotting, set the plant at the same depth at which it was growing; do not cover the woody base with soil.
Outdoors, plants make striking specimens in the ground or in large containers; they are not browsed by deer. A mature plant can endure 18F for brief periodsbut young plants in pots will quickly freeze to death at even a few degrees higher than this, so bring them indoors when necessary.