Asclepias eriocarpa, Indian Milkweed

Asclepias eriocarpa, Indian Milkweed

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Asclepias eriocarpa

Also known as Kotolo milkweed, his tough and widespread shrub, growing to 3' tall, is an important host plant for monarch butterflies. It has white to cream-colored flowers, sometimes with a tinge of purple. The attractive blue-gray leaves are hairy with a noticeable midvein, and the fruits are fat, tapering to a blunt tip. This species is widely distributed throughout the state, except in montane regions. It's found in dry rocky areas and also along stream banks. I first collected it near Gorman, California.

Ecological Function:

The native milkweeds are famous for being host plants for the monarch butterfly. The butterfly lays its eggs on milkweed plants and only on milkweed plants, which supply the toxins needed to protect the egg as it turns into a caterpillar. Research on the reasons for monarch extinction emphasizes the presence of native milkweed  as a major factor in successful monarch reproduction. Milkweed can be seen in summer covered with the green caterpillars that will turn into a chrysalis, and which then will then become the butterfly. It grows 2-4' tall in full sun and can handle some shade. It spreads through underground rhizomes. The plant goes dormant in the late summer. 

Do not plant non-native milkweeds. They don't contain the necessary alkaloids for monarch survival.

Growing Procedures:

There are 75-100 seeds per packet, enough for at least 25 to 35 plants. Milkweeds need cold-stratification, which simulates cold weather. Place seed on damp paper towel. Put the towel and the seed in a plastic bag and place in a refrigerator. This is "cold-stratification." After a month, sow the seeds in a warm greenhouse. The seeds will appreciate some warmth to germinate. 


We recommend using species that grow in your region, if possible. Coastal gardeners should think twice before planting milkweeds, which may not have grown there historically. It can create problems to draw migratory species out of their regular patterns. For example, some species may not have resistance to the fungi stimulated by fog. The caterpillars that will develop on that plant may not survive, thereby "wasting" the eggs of that species.

Give them full sun, and once they are established water only occasionally. These plants go dormant in late summer and fall. They spread through rhizomes into large clumps, and make a beautiful display.

It is hard to resist slitting the fat fruits along the seam with a fingernail, to watch the flat brown seeds with their feathery attachments float through the air. Though monarchs may overwinter along the coast, they breed inland, and it is here that restoring milkweed can be most effective. This plant may go dormant in colder gardens.

Indian Milkweed is grown as part of a program initiated by the Xerces Society, one of whose goals is to protect our waning Monarch butterfly populations. The demise of inland populations of milkweed, which are necessary to Monarch reproduction, are a big part of the problem. Widespread use of herbicides is another. Go to for more information.

There are 75-100 seeds per packet, enough for 20 to 30 plants, at least.