asclepias: milkweed

There are over 200 species of Asclepias worldwide, and more than 70 of those native to North America; about a half-dozen can be found in parts of Oregon. It is highly useful as both a nectar plant for adult butterflies and as a food source for the growing caterpillars.


The milky substance in the stem and leaves of the plant that give it its common name contains a chemical compound that, when ingested by the caterpillar, acts as a repellant to predators.And some species of the plant are more compatible with specific species of butterflies, in terms of their protective qualities.

This is especially true for the Monarch butterfly and Asclepias speciosa, as it is the only food source for the Monarch caterpillars!

As habitat in the wild is lost to development, maintaining compatible food and nectar supplies for butterflies becomes even more important.

Monarch In May

Besides their usefulness as a butterfly plant, the milkweeds are also beautiful. Leaves broad or thin, standing generally 2-3 feet tall (sometimes taller), with rounded clusters of tiny flowers that look like small stars, often in a mixture of creamy white and pink, sometimes deepening to a rich purple.

Monarch-butterfly egg

Monarch Butterfly eggs on Milkweed

Asclepias requires excellent drainage and a mostly- to full-sun location; yellowing leaves indicate either too much water or poor drainage. Too much retained water can also result in root rot.

But in general, all species of butterfly weed are virtually pest and disease-free (if you notice the leaves on your plant are being eaten, you may have successfully attracted butterflies to your garden!).

Asclepias speciosa (5258350992)

Asclepias speciosa: Showy milkweed

Showy milkweed grows through the Willamette Valley and is the most commonly available Asclepias in nurseries. It also hosts Monarch butterflies at every stage of development! In addition, the nectar provided by its flowers is popular with hummingbirds, bees and other types of butterflies.

Pink flowers bloom from late spring to mid-summer. Blue-green lance-shape leaves are up to 6" long and have a thin layer of white fuzz. Showy milkweed adapts to conditions on both sides of the Cascades, but good soil drainage is important.

Grows to 3’ x 3', Sun, Hardy Z3


Asclepias fascicularis: Narrowleaf milkweed

Long, narrow leaves in whorls up the stems of this 2.5’ milkweed. Flowers are generally purplish-pink and white. It grows in dry to moist soil, near streams and at the coast — but note, in sandy (fast-draining) soil.


Asclepias cordifolia: Heartleaf milkweed

Elongated heart-shaped leaves, purple flowers arranged in more open, drooping umbels. This one is found in the dry spots of southern Oregon and into California. Extremely drought-tolerant once established, requires next-to-no summer water.

Asclepias incarnata: Swamp milkweed

An exception to the rule: This an Asclepias that grows in wet conditions. Grows 3-4’ tall, narrow green leaves and clusters of bright pink flowers. Not native to Oregon (the farthest west it gets is Idaho, but if you have a wet garden, there is a butterfly weed for you too!)