grab this plant by the horns (no, don't)
perennial plant, 1-2.5' tall and wide
greenish white flowers spring through fall followed by horn shaped pods
moderate water (terrace zone)
FULL TO PART SUN
HARDY TO –10 to –20°F
LARVAL FOOD plant for monarch butterfly, nectar food plant for butterflies, bees
Native to the SW United States and Northern Mexico, antelope horns (Asclepias asperula) are one of the many species of milkweed that host the larvae of the monarch butterfly. Spring through fall, erect umbels emerge bearing greenish white and maroon flowers that form broad round clusters (strongly contrasting the bright green leaves). The flowers are followed by mature seed pods that curve upward approximating the form of an antelope horn (thus the common name).
These perennial herbs grow 1-2 feet tall, rarely to almost 3 feet. Plants take full to part sun (but not too much shade if you want them to bloom nicely), moderate water, and well-drained soil. They can take temperatures as low as –10 to –20°F. Antelope-horns will inevitably have aphids. The insects are not a problem unless the plant looks sick; at that point an effective treatment is to spray the plant and aphids with soapy water. Another possible treatment is to support the plant part with your hand and blast it with high-pressure water. We actually never treat plants, because the aphids attract ladybugs and don't seem to ever harm the plants.
As with all members of the genus Asclepias, this plant is a nectar-producing maniac attracting all sorts of butterflies and native bees.