Is tropical milkweed bad for monarchs?

Tropical milkweed (Asclepias curassavica) is a milkweed, and monarch caterpillars eat it; The Gardens at Texas A&M keep some “to provide a variety of monarch host plants during the spring.”¹ The problem is where it stays green through winter. Monarch Joint Venture: “In parts of the southern U.S. and California, the year-round persistence of tropical milkweed allows monarchs to breed throughout the winter,” and those winter patches spread a parasite called OE.² So the answer depends on where you live. In Texas, cut it back in fall and winter and replace it with natives. In south Florida, Monarch Joint Venture’s own advice does not apply. In California, near the coastal groves where western monarchs winter, the Xerces Society says not to plant milkweed of any kind.

What the sources say

Monarch Joint Venture’s fact sheet, whose contributors include Sonia Altizer, Karen Oberhauser and Lincoln Brower, is the most specific statement. It says the plant “is not native to the United States or Canada,” and that it “is attractive and easy to grow, so it tends to be the most widely available milkweed at commercial nurseries.”² The mechanism: “These year-round tropical milkweed patches foster greater transmission of the protozoan Ophryocystis elektroscirrha (OE), increasing the likelihood that monarchs become infected with the debilitating parasite.” The numbers: “49% of winter-breeding monarchs were infected with this parasite, compared to 9% of migratory monarchs sampled in Mexico and 15% of migratory monarchs sampled in the northern U.S. and Canada.”²

The fact sheet prints the counterargument too: tropical milkweed’s toxins “can lower OE replication within infected monarchs,” but “this could actually promote disease spread by allowing moderately infected monarchs that otherwise would have died quickly following eclosion to live longer and spread more parasite spores.”² Its recommendation: “Plant only species of milkweed that are native to your region, whenever possible.”²

The Xerces Society, in its Southern Plains nectar guide: tropical milkweed “can persist year-round in mild climates, allowing monarchs to breed throughout the winter rather than going into diapause,” and “may foster higher loads of a monarch parasite called Oe (Ophryocystis elektroscirrha), which negatively impacts monarch health. Because of these implications, we recommend planting native species of milkweeds in areas where they historically occurred.”³ Its rearing guidance: “it is best to remove these species and replace them with native milkweed if appropriate.”⁴

Texas

The plant is recorded as naturalized only in far south Texas (Cameron and Hidalgo counties) and southeast Texas, according to Texas Parks and Wildlife’s milkweed identification guide, which takes no position on planting it.⁵ The position that does exist comes from a 2015 article in the agency’s Eye on Nature newsletter, by Ben Hutchins: “Researchers have expressed concern that widespread cultivation of this admittedly beautiful plant may actually be detrimental to monarchs by increasing infection rate by a protozoan parasite, and by causing migrating monarchs to reproduce in the winter when they should be migrating. We do not recommend this plant. If you do decide to plant tropical milkweed, cut the plants back and trim newly sprouting leaves throughout the late fall and winter, so that the plant is unavailable for use by southbound monarchs.”⁶ That is a signed newsletter article, not a published agency policy. The Native Plant Society of Texas will not fund it: “Under no circumstances can NPSPOT funds be used for Tropical Milkweed, Asclepias curassavica.”⁷

Mike Arnold, who directs The Gardens at Texas A&M and keeps some tropical milkweed there for spring hosting, describes the practice: “we prune our tropical milkweed all the way to the ground as we approach fall,” because “if you don’t prune it back, some of the butterflies may be tempted to stay because they have a steady source of food.”¹

The question matters most on the Texas coast, where some monarchs stay all year. The Fish and Wildlife Service places non-migratory monarchs “in parts of Florida, the Gulf Coast and California,” and Butterflies and Moths of North America says monarchs “may breed all year in Florida, South Texas, and southeastern California.”⁸⁹ The native replacements, by region, are on when to plant milkweed in Texas.

Florida

Florida is the exception the fact sheet itself makes. Its recommendations carry a footnote: “These recommendations are not applicable in south Florida (south of Orlando), where a distinctive, non-migratory population of monarchs has long been established.”² The University of Florida’s extension service describes that population: “Because of the warm climate and continuous availability of host plants, much of Florida’s monarch population stays in the state year-round and breeds continuously throughout the year. Year-round residents are more common in southern Florida, as cold winter temperatures in northern Florida can kill monarchs at any life stage.”¹⁰ The Fish and Wildlife Service’s Southeast office: “Some live in southern Florida year-round.”¹¹

So south of Orlando, the cut-back advice does not apply, by the word of the people who wrote it. North of Orlando, the fact sheet’s advice stands as it does elsewhere in the South. We have not yet gathered a Florida-specific native milkweed list to the standard we use for Texas, so this page does not name one.

California

California is inside the fact sheet’s “southern U.S. and California,” and the western population adds a second reason. Western monarchs winter in groves along the coast, and the Xerces Society wrote in 2018: “we do not recommend planting tropical milkweed, and further suggest milkweed of any species not be planted within one mile of monarch overwintering sites in California.”¹² In 2021 it wrote that “planting milkweed near overwintering sites (within 5 miles) has generally been discouraged.”¹³ Monarch Joint Venture’s rule of thumb: “you should only plant milkweed if it occurred historically in your region and you live more than 1 mile away from an overwintering site.”¹⁴ The published distances disagree, one mile against five, so we say “near the groves” and cite both.

The Xerces Society also reports that “resident populations occur in Florida, along the Gulf Coast, and in Southern California,” and that “more recently it appears that a resident population is forming in the Bay Area in California as well.”¹³ The western population is small: volunteers counted “approximately 12,260 monarchs” at the end of 2025, against “the low millions regularly in the 1980s.”¹⁵

Farther north

Monarch Joint Venture: “Tropical milkweed might pose fewer problems in the northern monarch breeding range because it dies back naturally when it freezes.”² Might, in its words; the recommendation to plant native species still stands.²

If you already have it

Nobody is wrong for having bought it; it is what was on the shelf. Monarch Joint Venture’s instruction: “prune the milkweed stalks to about 6 inches in height during the fall and winter months to discourage monarchs from establishing winter-breeding colonies. Cutting back the milkweed will also help to eliminate OE spores that may be present on the plant. Re-cut the milkweed every few weeks as leaves re-sprout.” Then the plant “should be gradually replaced with native milkweeds as they become available.”² The Eye on Nature article and Texas A&M’s Mike Arnold say the same in their own words, differing only on how far to cut; the fact sheet’s six inches with repeat cuts is the most specific instruction, and the one we follow.⁶¹

How we know. Monarch Joint Venture’s OE fact sheet and planting FAQ, the Xerces Society’s Southern Plains guide and its 2018 and 2021 posts, Texas Parks and Wildlife’s milkweed guide and its 2015 newsletter article, the Native Plant Society of Texas, Texas A&M AgriLife, the University of Florida’s extension service, the Fish and Wildlife Service and Butterflies and Moths of North America. Every quotation above is taken from the source named.