Mexican Butterfly Weed Care & Planting Guide (Asclepias curassavica)

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how to grow mexican butterfly weed asclepias curassavica
Mexican butterfly weed has yellow, orange, and/or red flowers that are slippery, causing insects to literally fall into their pollen. Photo by © 2016 Jee & Rani Nature Photography, CC BY-SA 4.0

Asclepias curassavica is commonly known by many names, including Mexican butterfly weed, bloodflower, and tropical milkweed. The milkweed genus, Asclepias, is named for the milky substance that the plants exude when cells are damaged. Mexican butterfly weed is native to the American tropics and can be found throughout North America as an ornamental plant. It produces eye-catching orange and red flowers in flusters at the tops of its stems. These blooms are strong attractants of a variety of pollinators.

Mexican butterfly weed is a controversial plant: although it can be a beautiful addition to some gardens as a food source for butterflies, it is believed to be harmful to monarch butterflies in particular. Asclepias curassavica can grow later in the year than native milkweed species, prompting monarchs to breed at times when they should be overwintering.

Additionally, native milkweed plants in the range of monarch butterfly migrations die back after blooming. Mexican butterfly weed however, does not die back, which can lead to dangerous health problems for monarchs.

Facts, Benefits & Uses of Mexican Butterfly Weed

is mexican butterfly weed bad for monarch butterflies
Although Asclepias curassavica is beneficial to a variety of pollinators, it can be detrimental to monarch butterfly populations.

Mexican butterfly weed produces beautiful orange and red blossoms that are very attractive to butterflies. For this reason, it is a popular choice for pollinator gardens, bringing in bees, butterflies, moths, and even hummingbirds. However, planting Mexican butterfly weed outside of its native region, especially in range of monarch butterflies, is often highly criticized because of its negative impacts on monarchs.

While Mexican butterfly weed can certainly sustain monarch caterpillars, its perennial growth leads to problems with migration patterns and health. Considering the fact that monarch butterflies are experiencing a steep decline in population numbers, it is important to consider the protection of this iconic species.

Like other members of the Asclepias genus, tropical milkweed has a unique mode of pollination. The center of each flower contains structures called hoods, which in this species are the yellow/orange portions of the flower, while the red portions are the actual petals. These hoods contain pools of nectar to draw in pollinators, and at the base of each hood is a smaller structure called a horn. These horns are very steep and slippery, causing any insects that land on them to essentially slip down into the center of the flower. This insect will then come into contact with the plant’s pollen sacs, which come in pairs; each pair of pollen sacs is connected by a thin, stringlike structure called a translator arm. The insect will essentially fall into the translator arm and break it, allowing the pollen sacs to be freed.

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Mexican Butterfly Weed Fact Sheet:
Herbaceous Perennial
USDA 9 – 11
Full sun
Orange, yellow, red
June – October (Summer to Fall)
Height 60 – 90 cm (24 – 35 in)
Place seeds ¼ inch below soil surface
pH 6.5 – 7.5

Mexican Butterfly Weed Growth, Hardiness & Climate

mexican butterfly weed seeds
Mexican butterfly weed reseeds readily, enabling its fast growth and spread. Photo by SAplants, CC BY-SA 4.0

Mexican butterfly weed grows quickly, reaching a maximum height of 2-3 feet in its first year. This plant re-seeds easily, and therefore can spread with little trouble.

A. curassavica is a unique plant in that it produces flowers continuously during its blooming season of June to October. As some blooms go to seed, the plant produces new flowers, prolonging the season in which you can enjoy its bright orange and red flowers. Mexican butterfly weed will survive for years if grown in hardiness zones 9 to 11. Outside of these zones, Mexican butterfly weed acts as an annual, as it does not overwinter when exposed to frost. Due to its ability to easily reseed, Mexican butterfly weed can still be a good option outside of its set hardiness zones.

How to Plant Mexican Butterfly Weed Near Ponds

how to plant mexican butterfly weed
Mexican butterfly weed prefers moist soils, and so does well when planted near garden ponds.

An easy plant to establish in your garden or the edge of your pond, Mexican butterfly weed grows well from seeds. In hardiness zones 9 to 11, simply sow seeds directly in the ground in the spring. Below zone 9, start seeds indoors two months before the last frost of the season.

Mexican butterfly weed can also be grown from cuttings if desired. Young plants can be easily transplanted, but mature plants produce a long taproot, making transplantation difficult. If you do not remove developing seed pods, Mexican butterfly weed will happily reseed.

How to Care For Mexican Butterfly Weed

how much sun does tropical milkweed need asclepias curassavica
Tropical milkweed grown in the shade will have fewer flowers than those grown in full sun. Photo by (c)2006 Derek Ramsey, CC BY-SA 2.5

Mexican butterfly weed does best when exposed to full sun, although it can be tolerant of partial shade if necessary. This will lead to more lush foliage and fewer blooms, as more energy will be devoted to creating leaves to obtain more light. You will get the most flowers out of your plant if it has the benefits of full sun and moist, well-drained soil. However, it can tolerate some amount of dryness once established as mature plants develop a deep taproot.

Outside of its native range of the American tropics, gardeners are encouraged to cut back tropical milkweed in the fall in order to avoid negatively impacting monarch butterflies and native plant species that it may displace.

How to Winter Mexican Butterfly Weed

Mexican butterfly weed is a winter-hardy perennial in zones 9-11. This plant will not die back in the winter in these zones. Many people choose to grow Mexican butterfly weed even outside of zones 9-11; in this situation, the plant will die when exposed to frost and is essentially treated as an annual. It is an option to try to overwinter Mexican butterfly weed inside, although it will likely be difficult to provide the plant with the necessary levels of sunlight.

Is Mexican Butterfly Weed Toxic, Poisonous or Invasive?

Mexican butterfly weed is considered to be invasive outside its native areas, due to its fast growth and enthusiastic reseeding. This plant can have negative impacts on monarch butterflies, so careful consideration should be made when planting. If you are set on choosing Mexican butterfly weed for your garden, be sure to plant it in pots and remove dead flower heads before they go to seed to prevent spreading.

Like many other milkweed species, Mexican butterfly weed is known to be toxic to humans, cats, dogs, horses, and livestock due to high levels of cardenolides. It is not known whether Mexican butterfly weed is toxic to fish, so take care when planting near a pond or stream.

Is Mexican Butterfly Weed Edible? Will Fish Eat it?

Mexican butterfly weed is not edible and is in fact toxic. The good news is that Mexican butterfly weed does not tend to taste good to animals, and many will avoid eating it. There is no evidence that pond fish will try to eat Mexican butterfly weed, but it is probably best to keep it out of reach due to its confirmed toxicity in other organisms.

Where to Buy Mexican Butterfly Weed & Seeds? (UK & US)

Mexican butterfly weed is easily obtained from plant nurseries in North and South America, both in person and online. Elsewhere, you may have to order it online. Please be aware of whether you are planting non-native species in your area!

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