Milkweeds (Asclepias spp.) are well-known as the host plants for monarch butterfly caterpillars, playing a critical role in the butterfly’s life cycle. As milkweed populations are declining and the monarch is moving toward the endangered species, increasing numbers of gardeners are adding the plant to their cultivation list. In California, they can choose between 15 species of milkweed native to the state.
Milkweed and the Monarch
Milkweeds are drought-tolerant plants that occur in nearly all of the ecosystems in California. Although the 15 native species of milkweed in California are best known for the role they play in the life cycle of monarch butterflies, the showy flowers with their high quality nectar actually help support a wide range of pollinators, from honeybees to hummingbirds.
Milkweed gets its name from the sap, which is milky. It contains alkaloids, complex chemicals that help to preserve milkweed for pollinators, since it renders the plants inedible for most animals. These plants are so bitterly flavored and unpalatable that range animals will avoid eating them if anything else is available.
Native California Milkweed
Many of the native milkweed species in California are extremely difficult to find in garden stores, which makes it hard for gardeners to welcome them into the garden. Seeds from the most common species of native milkweed are easier to find commercially. These include heartleaf milkweed, desert milkweed, woollypod milkweed, showy milkweed, and narrowleaf milkweed.
Xerces Society is an invertebrate conservation group that concerns itself with milkweed cultivation. They have made recommendations regarding which native California milkweed to plant in your garden. Their first choice is narrowleaf milkweed, Asclepias fascicularis. This common species will do well in gardens across much of California and serves as a good milkweed for southern California.
Narrowleaf milkweed grows to some 3 feet (91 cm.) tall with pink and white flowers. It blooms for a long period, from May through October, offering enough nectar for adult monarchs and also other species of beneficial insects. Deadheading the plants by removing spent blooms will prolong this blooming season.
Milkweed for California
The other species of milkweed (California native) recommended by the Xerces Society is showy milkweed, Asclepias speciosa. These plants do make a statement, growing up to 4 or 5 feet (1-1.5 m.) tall with a bloom time similar to the narrowleaf milkweed. They tend to grow best in areas where tall trees grow (think redwoods), but will thrive anywhere in naturally moist garden soil.
Showy milkweed produces thick umbels of eye-catching pale pink flowers. The blooms are fuzzy and pink and offer a lovely fragrance. The plant spreads by underground rhizomes, forming an expanding clump. It can even spread aggressively in good soil.
The Xerces Society has done more than recommend these varieties. It has taken action to make seeds of both narrowleaf and showy milkweed available through retail nurseries. It also publishes the California milkweed guide that includes a list of nurseries offering the seeds.
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Teo Spengler has been gardening for 30 years. She is a docent at the San Francisco Botanical Garden. Her passion is trees, 250 of which she has planted on her land in France.
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