Photo copyright © 2018 Mariposa Native Plants
A native perennial herb, with white, pink, or purple flower clusters and long, veined, narrow pointed leaves, attached oppositely to strong, upright stems. The plant emerges in the spring and thrives throughout the hot summer, relying upon its deep root system. It produces large seed follicles later in the summer, which break open to disperse seeds attached to white, fluffy fibers. A.speciosa is winter deciduous. Along with several other species in the milkweed genus, this plant is a host for the monarch butterfly caterpillar.
A.speciosa is found in diverse environments throughout western North America. Within California, it grows in flatter terrains of the Sierra Nevada, the Sierra foothills, and the Coast Range north of San Francisco Bay. Elevation: sea level to 8,000 ft. (2500m). Sun: full or partial. Temperature: cold tolerant to 0°F (-20°C). Soil: clay or sandy; pH 6-8.
Try to get the plant in the ground as soon as is practical; A.speciosa does not like life in the container. However, it is easy to care for once established. Prefers a site that is well-drained. Roots are sensitive to disturbance; avoid breaking the root ball when planting from the container. Water (.5 gallon, 2 liters) once per week until the first winter. Water once per month, same amounts, in the second summer. Thereafter, no supplemental water required. This milkweed can grow to be 3-4 feet tall (1-1.3m). A.speciosa propagates through rhizomes and can form large clumps; this is good for the monarch butterfly, but plan your site accordingly.
A.speciosa is a host plant for the monarch butterfly's caterpillars. Milkweeds, and A.speciosa among them, contain within them an alkaloid that is mildly poisonous and distasteful to birds and other predators. However, the monarch has adapted to this natural fact, and the caterpillars can feed on the milkweed leaves and fine stems, absorb the alklaoid, and become quite unpalatable to predators.
Aphids: Young plants especially are subject to aphids. Brush the aphids off gently by hand, with a soft brush, or with a spray of water from the garden hose. Please do not use pesticides on A.speciosa, because these chemicals harm the monarch butterfly caterpillars. California native plants are adapted to withstand the insect pests, and they really don't need chemical help from you to do so. Also, the aphids are a prime food target for the helpful ladybug insect, so leaving a few of them on the plant confirms an established food and life cycle.
Gophers: Might eat at the roots of A.speciosa as a last resort.
Deer: Do not seem to browse on showy milkweed.
As might be guessed from its name, showy milkweed is a very attractive native plant. However, should it spread too much and become unruly, its roots can be cut back during the winter when it's dormant.
Sacramento Valley ecotype, #1 container (about 1 gallon).
Plumas County ecotype, #1 container.