Milkweed is the host plant for the Monarch butterfly which means it is the only plant the caterpillars can eat. The adult butterfly lays her eggs on the milkweed and the caterpillar eats the leaves for about 2-4 weeks until it is ready to pupate and become a chrysalis. Before making a chrysalis, the caterpillar usually crawls away from the plant to find a safe spot on a branch or structure to hang and develop. The adult butterfly emerges from the chrysalis after about 10-14 days. Since insects are cold blooded, all these stages are influenced by temperature - and take longer at lower temperatures. Narrowleaf milkweed is native to California and healthier for caterpillars than the non-native varieties. Like all native milkweeds, it goes dormant in the winter, seeming to disappear, but returns in the spring.
You can scatter these seeds in your garden during the fall, winter or early spring and let winter rains water the seedlings. It also works well to plant them in pots or 6 packs to get them started, and then transplant out in the garden in the spring or early summer. Milkweeds are deep rooted so need a lot of depth if planted in pots.