Asclepias curassavica (Tropical Milkweed)

Asclepias curassavica, commonly known as Tropical Milkweed, is a vibrant, fast-growing evergreen perennial with striking clusters of red, orange, and yellow flowers. It provides a vital nectar source for butterflies, bees, and hummingbirds. Monarch butterflies lay eggs on its leaves, supporting their life cycle. Unlike native milkweed species, it does not die back in winter in warm climates, raising concerns about its impact on monarch migration.

Milkweed plants belong to the Apocynaceae family, which also includes oleander, hoya, plumeria, and the desert rose. These plants are known for their importance to pollinators and play a vital role in maintaining biodiversity.

Description

Tropical Milkweed is a tender evergreen perennial native to the American tropics, thriving in warm climates where it grows year-round. From spring to fall (year-round in warm climates), it produces striking clusters of orange-red flowers with yellow hoods, earning it the common name “bloodflower.” These vibrant blooms give way to long, narrow seed pods in fall, which split open to reveal seeds adorned with silvery-white, silky hairs, aiding in wind dispersal.

The plant features slender, lance-shaped green leaves and upright stems that produce milky sap when cut. Unlike temperate milkweed species that die back in winter, Tropical Milkweed remains evergreen in frost-free areas, allowing monarch butterflies to breed continuously. However, this prolonged growth cycle has raised concerns regarding its impact on monarch migration patterns.

Native Habitat

Tropical Milkweed is native to Mexico, Central America, South America, and the Caribbean. It thrives in open fields, roadsides, disturbed lands, and meadows, preferring warm, sunny conditions. While widely cultivated in North America, it is considered non-native in the United States and Canada.

Due to its adaptability, Tropical Milkweed has naturalized in many regions outside its native range, including parts of the southern U.S., where it grows as a perennial. In colder climates, it behaves as an annual, completing its life cycle within one growing season.

Plant Type and Habit

• Plant Type: Tender perennial
• Growth Habit: Upright, bushy
• Lifespan: Perennial in warm climates, annual in colder regions
• Root System: Fibrous root system

Size

• Height: 24-36 inches (60-90 cm)
• Spread: 12-24 inches (30-60 cm)

Although it self-seeds readily in warm climates, Tropical Milkweed (Asclepias curassavica) remains more compact than common milkweed (Asclepias syriaca), making it a good choice for gardens, borders, and container plantings.

Flowers and Fruits

• Flower Color: Red, orange, and yellow
• Bloom Time: Spring to fall (year-round in warm climates)
• Flower Shape: Small, star-shaped flowers arranged in flat-topped clusters (umbels), measuring 2-4 inches (5-10 cm) across. Each cluster typically contains 6 to 15 individual flowers.

Following flowering, the plant produces elongated seed pods that split open when mature, releasing silky seeds dispersed by the wind.

Foliage

• Leaf Shape: Lanceolate (narrow and pointed)
• Leaf Size: 4-6 inches (10-15 cm) long
• Leaf Color: Medium to deep green

Leaves grow in opposite pairs along the stems and exude a sticky, white sap when broken.

Hardiness

Tropical Milkweed thrives in USDA Zones 8-11, where it can grow as a perennial in warm climates. However, it is highly sensitive to frost and does not survive freezing temperatures, often behaving as an annual in colder regions.

Uses in the Garden

• It is ideal for butterfly gardens, pollinator habitats, rock gardens, and naturalized meadows.
• Bright flowers add color to mixed borders, wildflower plantings, and container gardens.
• Milkweed: Is it Right for Your Garden? Pros and Cons Explained

Wildlife Value

Tropical Milkweed attracts a variety of pollinators, including bees, butterflies, hummingbirds, and moths. The plant serves as a host for the larvae of the Monarch Butterfly, Milkweed Tussock Moth, and other Danainae butterflies, including the Queen Butterfly.

While monarch butterflies are drawn to its vibrant flowers, native milkweed species are a better choice for supporting their populations. Unlike native milkweeds that go dormant in winter, Tropical Milkweed can remain green year-round in warm climates, potentially disrupting monarch migration patterns.

In regions like California, Texas, Florida, and South Carolina, its continuous growth encourages monarchs to linger instead of migrating, increasing their exposure to disease and altering their life cycle.

Tropical Milkweed can also harbor the protozoan parasite Ophryocystis elektroscirrha (OE), which infects monarch butterflies. As monarchs visit the plants, they unknowingly deposit OE spores on the leaves. When caterpillars hatch and consume the foliage, they ingest the parasite, leading to weakened butterflies with reduced migration success, lower body mass, shortened lifespan, decreased mating success, and impaired flight ability, ultimately affecting the eastern monarch population.

Milkweed plants are essential for monarch butterfly survival, providing the sole host for their larvae. Over the past 20 years, North America’s monarch population has declined by 90%, making milkweed conservation more critical than ever.

Due to concerns about its impact on monarch populations, gardeners outside of Tropical Milkweed’s native range are encouraged to plant regional native milkweed species, such as showy milkweed, narrowleaf milkweed, and desert milkweed.

Toxicity

Tropical Milkweed contains toxic compounds that can be harmful to humans and animals if ingested in large quantities. The plant’s milky sap contains cardiac glycosides and resinoids, which can cause mild to moderate poisoning.

All parts of the plant—including the bark, flowers, fruits, leaves, roots, seeds, and stems—are toxic. Ingestion can lead to stomach upset, nausea, vomiting, abdominal pain, diarrhea, weakness, lethargy, and confusion. Additionally, the milky sap can cause skin irritation, contact dermatitis, and eye irritation if touched.

Tropical Milkweed is toxic to cats, dogs, and horses. Symptoms of poisoning in animals include gastrointestinal distress, drooling, vomiting, diarrhea, lethargy, irregular heartbeat, and weakness. In severe cases, ingestion may lead to cardiac issues.

Deer and Rabbit Resistance

Tropical Milkweed is naturally resistant to deer and rabbits due to its milky sap, which contains toxic cardiac glycosides.

Invasiveness

Tropical Milkweed does not spread aggressively by rhizomes. However, it readily self-seeds, potentially leading to unintended spread.

How to Grow and Care for Tropical Milkweed

Light

• Requires full sun for optimal growth and flowering.

Soil

• Prefers well-drained, sandy, or loamy soil. Can tolerate poor soil but does not thrive in heavy clay.

Watering

• Water regularly until established; drought-tolerant once mature.

Fertilization

• Low fertilizer requirements; a light application in spring can promote growth.

Pruning

• In frost-free areas, cut back in fall to encourage new growth and prevent monarch parasites.

Common Problems and Pests

Since tropical milkweed is a valuable plant that attracts pollinators and beneficial insects, the use of pesticides should be avoided, as they can harm butterflies, bees, and other helpful species.

Common Pests

• Aphids – Bright orange Oleander Aphids can be a nuisance, clustering on stems and leaves. They feed on plant sap, sometimes causing leaf curling or yellowing. However, they are easily managed by spraying the plant with a strong jet of water from a hose or introducing natural predators like lacewings and ladybugs.
• Spider mites – In hot, dry conditions, spider mites may infest milkweed, leading to stippled leaves and webbing. If an infestation occurs, cutting back and discarding affected plant material is an effective control method.
• Milkweed Bugs (Oncopeltus fasciatus) – These bright orange and black insects feed on the seeds and plant tissue but are not harmful to the plant. In fact, they help regulate the number of seeds dispersing in the wind, preventing excessive self-seeding. Because they contain toxic compounds from milkweed, they have few natural predators.

Disease Issues

Tropical Milkweed is generally resistant to diseases, but prolonged wet or humid conditions may promote fungal infections such as powdery mildew or leaf spot diseases. To prevent disease:

• Ensure good air circulation by spacing plants appropriately.
• Avoid overhead watering to keep foliage dry.
• Remove infected plant material if necessary.

How to Propagate Tropical Milkweed

Tropical Milkweed can be propagated by seeds or cuttings, both of which are relatively easy and reliable methods.

From Seeds

Tropical Milkweed produces long, slender seed pods that split open in fall, revealing silky-haired seeds that are wind-dispersed. To propagate from seeds:

• Harvesting Seeds: Collect seeds once the pods have ripened but before they fully split open to prevent loss. Place them in a paper or burlap bag to contain the seeds.
• Seed Viability: Seeds remain viable for a long time, though fresher seeds have higher germination rates.
• Direct Sowing: In warm climates (USDA Zones 8-11), seeds can be directly sown into the soil in fall or early spring.
• Indoor Sowing: In cooler climates, start seeds indoors 6-8 weeks before the last frost. Sow them in well-draining seed-starting mix, pressing them lightly into the surface.
• Germination Conditions: Keep soil moist but not soggy. Seeds typically germinate in 7-21 days at temperatures between 70-85°F (21-29°C).
• Transplanting: Once seedlings have at least two sets of true leaves, harden them off before transplanting outdoors into well-draining soil in a sunny location.

From Cuttings

Tropical Milkweed can also be propagated through stem cuttings, a faster method that ensures the new plants maintain the same characteristics as the parent plant.

• Selecting Cuttings: Take 4-6 inch (10-15 cm) cuttings from healthy, non-flowering stems in late spring or early summer.
• Preparing the Cuttings: Remove the lower leaves, leaving only the top few leaves. Dip the cut end in rooting hormone to encourage faster root development.
• Planting Cuttings: Insert cuttings into a pot filled with moist, well-draining soil or place them in a glass of clean water.
• Rooting Conditions: Keep the cuttings in a warm, bright location with high humidity but out of direct sunlight. If planted in soil, maintain even moisture. If in water, change the water every few days.
• Transplanting: After 2-4 weeks, once roots have developed (about 1-2 inches long), transplant the cuttings into individual pots or directly into the garden.

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