Asclepias curassavica aka Tropical Milkweed

Asclepias curassavica has two common names: tropical milkweed and blood flower. It is part of the dogbane family, Apocynaceae. It grows wild from Mexico through tropical America. It grows in pastures, fields, waste ground, and along roads. Plants that escaped gardens have spread through many tropical regions. This perennial lives for years but cannot withstand frost. In cooler gardens, people often grow it as an annual. In warm places, it can keep its leaves through winter.

Garden plants reach about 2–3.3 feet [0.6–1 metre] tall. They spread about 1–2 feet [0.3–0.6 metres] wide. Reports from the tropics give heights to 4.9 feet [1.5 metres]. Some plants reach 8.2 feet [2.5 metres]. The stems grow upright and may branch. They can turn woody near the base. Damaged leaves and stems give off white, milky sap. The green leaves are narrow and have smooth edges. Some have a pale vein down the middle, called a midrib. A long taproot makes grown plants hard to move.

The orange-red flowers have yellow hoods. They grow in groups above the leaves. Missouri Botanical Garden gives a bloom season of June to October. North Carolina State reports blooms from spring through fall. Bees, wasps, and butterflies bring pollen to the flowers. The plant also draws hummingbirds and moths. Brown, dry pods called follicles form after the flowers. They hold many seeds with tufts of hair. Wind carries these light seeds away from the plant. Gardeners cut the flowers and use dried pods in arrangements.

Grow this milkweed in full sun and rich soil that drains well. Loam and sand suit it, with acid or neutral pH. Give it moderate water while it grows. Water less after it blooms. Keep it almost dry in winter. Missouri Botanical Garden lists USDA zones 9–11. North Carolina State also lists zone 8. The RHS rates it H1C for UK conditions. Use sites free of frost. In colder areas, grow it under glass. It suits beds, borders, pots, and cottage gardens. It also suits areas where plants spread on their own.

Aphids may gather on the plant and lead to sooty mold. Whitefly can attack plants under glass. Serious disease is rare. Seeds can make it weedy where winters stay warm. Plants that persist can carry a parasite that harms monarch caterpillars. Their long bloom season may also disrupt monarch migration. For monarch gardens, North Carolina State advises using native milkweeds instead. There are no known food uses. Eating the plant can cause vomiting and diarrhea. It can also cause weakness and confusion. It poses risks to dogs, cats, and horses too. The sap can irritate skin and eyes. Traditional medicine uses several parts. But large doses of the root can kill. Other recorded uses include fibre from the stems and stuffing for pillows. People also bundle the stems to make brooms.