Horsetail Milkweed Plants (Asclepias subverticillata) Quick Facts!

Host plant to Monarch Butterflies, nectar plant to a large variety of butterflies.

Herbaceous perennial

Native to the southwestern and midwestern states

Hardy in USDA zones 5-8

Prefers full sun, will tolerate some shade

Well-drained, sandy soil, drought tolerant once established

Showy clusters of white flowers from mid to late summer

Grows about 2-4 feet tall

Space 1-2 feet apart

Propagated from seed or rhizome cuttings

Horsetail Milkweed Plants (Asclepias subverticillata)

Sweet fragrance wafts from creamy, star-shaped flowers clumped into rounded, feathery mounds that stand out among the long slender leaves of the Horsetail Milkweed. Cold-hardy to at least 0℉, the plant bounces right back in the spring. It is one of the easiest milkweeds to grow, thriving in well-drained, sandy soil and full to partial sun conditions. It is drought-tolerant once established.

Above all, though, the Horsetail Milkweed is one of the top favorite host plants for our beloved monarch and queen butterflies! Growing wild on sandy mesas and desert flats, in rocky plains and grasslands, this milkweed is a crucial plant for migrating monarchs.

The Truth About the Toxin

Is the Horsetail Milkweed truly toxic, though? Yes, it is. The plant manufactures a potent neurotoxin that will kill livestock if ingested in sufficient quantities. It is also this very toxin that makes the plant so utterly essential for monarchs. The larvae ingest the leaves without harm to themselves, but the poison makes them unpalatable to predators–a key means of defense for a chubby, slow little caterpillar! The toxin is so vital to larval survival that adult monarchs will lay eggs only on milkweed, and hatching caterpillars will eat nothing but milkweed foliage until they emerge from the chrysalis and metamorphosis into a butterfly is complete.

It’s important to note that the Horsetail Milkweed has a truly horrible taste that makes livestock leave it alone. Cattle only eat it in areas that are so overgrazed that no other sustenance is available or when the milkweed is harvested and incorporated into hay bales. In an effort to negate the possibility of including the plant in cattle food, today’s farmers have all but eradicated the Horsetail Milkweed from their fields…which has decimated a crucial element of the monarch butterfly’s life cycle.

This is Where You Can Make a Difference

If you are not harvesting your garden greens for hay and you don’t have a cow, planting Horsetail Milkweed may be a good way for you to make it possible for a few more butterflies to take their places in nature’s cycle. Try it in containers to contain its tendency to spread, and remember that several plants (six or so) are necessary to provide sufficient sustenance for a caterpillar on its journey to becoming a butterfly!

Monarch lovers in the Southwest region of the country–in the migratory pathways that lead to and from the butterflies’ Mexican haven–have the unique opportunity to help save a species by planting the Horsetail Milkweed.

Photo license: Creative Commons