Narrowleaf Milkweed
Asclepias fascicularis Decne.
The workhorse milkweed of the Pacific states and the backbone of western monarch recovery planting. Slim whorls of narrow leaves, dense clusters of small greenish-white flowers flushed pink, and an ability to shrug off a rainless California summer.
Also called Mexican Whorled Milkweed, Narrow-leaved Milkweed.
- Height
- 2 ft–4 ft
- Spread
- 1.5 ft–3 ft
- Flowers
- white, pink, green
- Bloom
- May to September
- Light
- Full sun
- Soil moisture
- Dry, Average
- USDA zones
- 6–10
- Leaves
- Whorled, narrow
- Sap
- Milky latex
- Roots
- Rhizomatous, spreads by root
- Stratification
- 30 days cold-moist
- Range
- 7 states
When it flowers
Narrowleaf Milkweed blooms May to September, peaking in June and July and August.
How to identify it
- Leaves narrow and often in whorls of three to five, but wider and softer than eastern whorled milkweed.
- Flower clusters are dense and rounded, greenish-white with a dull rose tinge.
- Stems slender, usually several from one crown, smooth or nearly so.
- Widely branched at the top when growing well.
Unfamiliar words are in the glossary, and the identification key will narrow a plant down from what you can see.
The parts that identify it
Ecology and wildlife value
The primary larval host for the western monarch population through California’s Central Valley and foothills. Tolerates the long dry summer that kills more mesic milkweeds, and re-sprouts vigorously after being grazed or mown.
Monarchs are not the only thing that will find it. Expect large milkweed bugs on ripening pods, oleander aphids on the stems, red milkweed beetles at the flowers and, in late summer, milkweed tussock moths. The flowers are a heavy nectar source, so bumble bees and large wasps work them hard, and they are the ones that actually move the pollen. Everything that lives on milkweed.
Growing narrowleaf milkweed
The right milkweed for a California, Oregon or Nevada garden. Deeply drought-tolerant once established, spreads slowly by rhizome, and goes summer-dormant if left completely dry. Sow in the fall to use winter rains, or stratify for a month and sow in spring.
Seed needs about 30 days of cold-moist stratification. Rhizomatous, spreads by root. See how to plant milkweed seed for the full method.
Cautions
Like other narrow-leaved milkweeds it is toxic to grazing stock in quantity, and it is the species most often implicated in western livestock poisoning. More on milkweed toxicity.
Where narrowleaf milkweed grows
Recorded in 7 states: Arizona, California, Idaho, Nevada, Oregon, Utah, Washington.
County records from USDA PLANTS, public domain. Cross-check against BONAP and your regional flora before making management decisions.
Frequently asked questions
What is the best milkweed to plant in California?
Narrowleaf milkweed (A. fascicularis) for most of the state, showy milkweed (A. speciosa) in the north and at elevation, and heartleaf or California milkweed in specific foothill habitats. Avoid tropical milkweed entirely, because California is frost-free enough to sustain year-round breeding.
References and further reading
Names, ranges and conservation status here are drawn from the databases below. Where those disagree with a regional flora, trust the flora.
- Plants of the World Online 94272-1. Royal Botanic Gardens, Kew. Accepted name, authorship and global distribution.
- GBIF 3170291. Global Biodiversity Information Facility. Aggregated occurrence records.
- iNaturalist 56851. Community observations, photographs and phenology.
- Wikipedia. General-audience article on this species.
- BONAP county distribution map. Biota of North America Program. County-level range map.
- NatureServe Explorer. Conservation status ranks at global and state level.
- World Flora Online. Nomenclature and synonymy.
- Woodson, R. E. (1954). The North American species of Asclepias L.. Annals of the Missouri Botanical Garden 41(1): 1–211. The monograph the modern taxonomy of the genus still rests on. View
- Flora of North America Editorial Committee (eds.) (2026). Flora of North America North of Mexico. Oxford University Press, New York and Oxford. Accepted names, keys and descriptions for the North American flora. View
- Royal Botanic Gardens, Kew (2026). Plants of the World Online. Facilitated by the Royal Botanic Gardens, Kew. Nomenclature and global distribution, keyed to IPNI name identifiers. View
- Kartesz, J. T. (Biota of North America Program) (2026). North American Plant Atlas. BONAP, Chapel Hill, North Carolina. County-level distribution maps, the basis for the ranges generalized here. View
- USDA, NRCS (2026). The PLANTS Database. National Plant Data Team, Greensboro, North Carolina. State-level distribution, wetland status and nomenclature. View
- Agrawal, A. A. (2017). Monarchs and Milkweed: A Migrating Butterfly, a Poisonous Plant, and Their Remarkable Story of Coevolution. Princeton University Press. The standard general account of the milkweed and monarch relationship. View
Cite this page
This page is licensed CC BY 4.0. Quote it, adapt it and reuse it, including commercially, as long as you credit Milkweed USA and link back.
Milkweed USA. (2026). Narrowleaf Milkweed (Asclepias fascicularis). Retrieved DATE, from https://milkweedusa.com/species/narrowleaf-milkweed/
"Narrowleaf Milkweed (Asclepias fascicularis)." Milkweed USA, 2026, https://milkweedusa.com/species/narrowleaf-milkweed/. Accessed DATE.
Milkweed USA. "Narrowleaf Milkweed (Asclepias fascicularis)." Last modified 2026-08-01. Accessed DATE. https://milkweedusa.com/species/narrowleaf-milkweed/.
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title = {Narrowleaf Milkweed (Asclepias fascicularis)},
author = {{Milkweed USA}},
year = {2026},
url = {https://milkweedusa.com/species/narrowleaf-milkweed/},
note = {Accessed DATE}
}