Asclepias subulata aka Rush Milkweed

Asclepias subulata, or rush milkweed, belongs to the dogbane family, Apocynaceae. It is native to southwestern North America. Its range includes Arizona, California, Nevada, Baja California, and Sonora. In California, it grows in desert washes and sandy ground. These sites lie below about 1,970 feet (600 metres). It is not native to Britain or Ireland.

This perennial reaches about 6.6 feet (2 metres) tall. Its form resembles that of an Ephedra. This gives some sense of its spare, rush-like shape. The sources give no clear measure for its spread. Nor do they describe its bark or leaves in detail. Its flowers have both male and female organs. Bees, butterflies, moths, and other insects pollinate them. The species account gives no flowering season or fruit description.

Grow rush milkweed in a sunny spot with good drainage. It can also grow in light shade. Light, sandy soil suits it, including soil low in nutrients. The cultivation notes also recommend rich or peaty soil. It accepts mildly acid, neutral, and mildly alkaline conditions. The account lists both dry and moist soil as suitable. Its desert habitat points to its value in dry planting schemes. PFAF lists USDA hardiness zones 5–9 and UK zone 6. That UK listing does not give an RHS hardiness rating.

Plant it in its final site while still small. Its roots do not tolerate disturbance well. Seed offers one route to new plants. Sow fresh seed under glass in autumn, or sow in late winter. Stored seed may need two to three weeks of cold treatment. Germination can take one to three months at 18°C. Grow seedlings under glass through their first winter. Set them out during active growth in late spring or early summer. Spring division is another option, but roots need careful handling.

PFAF records no known edible use for this species. It also notes a report that some Native American peoples considered it poisonous. Treat that warning seriously rather than using it as food. The account records traditional medicinal uses, but does not identify the parts used. These include uses to cause vomiting and purging. Latex from its leaves and stems can provide rubber. The source also lists it for cultivated beds and records no weed potential.