Latin Name: Asclepias speciosa
Common Name(s): Showy Milkweed
Family: Apocynaceae
Size: up to 4 feet tall. Can establish large colonies by spreading rhizomes.
Life Cycle: Perennial
Distribution: Western North America in a variety of habitats, particularly along roadsides and streams, in sunny woodland areas, and on dry slopes and hills.
Light Requirements: Full sun.
USDA Zone: 3 to 9b
Drought Tolerance: Fairly high once established.
Fire Risk: Presumably low while it is growing, given the fleshy leaves. If growing near a structure in a fire-prone area it is probably best to cut it down after it dies back and dries to avoid the seed fluff and dried plant matter fueling any fires.
Cultivation Notes
Once established, milkweeds tend to be tough and adapt well to the garden. Showy milkweed needs full sun and can adapt to a variety of soil conditions, but generally does not appreciate wet soil for long periods of time. Do not disturb the roots if you can help it. Once established the plants should do fine without summer irrigation, but make sure they receive regular water when young. Fertilization not needed, the plants do fine even in poor and gravelly soil. Slug control may be needed when the plants are young, as heavy feeding by non-native slugs can kill young plants. Simply remove slugs in the evening and kill in soapy water.
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Ecology
The interesting flowers bloom from May through June and are very attractive to pollinators. Many specialist insects feed on this plant, and this is a preferred host plant of the monarch butterfly. The seeds are consumed by birds in the winter, when few food sources are available.
Uses
Milkweeds are all toxic to some degree, containing cardiac glycosides. Showy milkweed is one of the least toxic and is completely safe to eat cooked, with a long history of use. The flower buds, seed pods, and shoots are nutritious and tasty. The flower buds can be boiled down into a sweet syrup and the latex refined into a kind of chewing gum. The root is of uncertain edibility, with some reports mentioning it being toxic in large amounts.
Propagation
Seed or by division (more difficult). Seeds are easily collected and can be sown directly in the fall or in spring. Sow just under the soil surface. Germination can be slow and often is irregular. If planting in the late spring, cold stratification will likely be needed for up to two months before germination will take place. I have found milkweeds in general to be finicky when first establishing them. Young seedlings need irrigation, at least for the first year or two. The seedlings are temperamental, so it is best to transplant carefully without disturbing the roots too much. Division is difficult as well, as milkweed resents disturbance, and division is best done in winter when the plant is dormant.