# Narrowleaf Milkweed (Asclepias fascicularis)

> 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.

Source: https://milkweedusa.com/species/narrowleaf-milkweed/  
Licence: CC BY 4.0 (Milkweed USA)

## Summary

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.

## Key facts

| Field | Value |
| --- | --- |
| Scientific name | Asclepias fascicularis Decne. |
| Genus | Asclepias |
| Family | Apocynaceae |
| Common names | Narrowleaf Milkweed, Mexican Whorled Milkweed, Narrow-leaved Milkweed |
| Status | Native |
| Height | 2 ft–4 ft |
| Spread | 1.5 ft–3 ft |
| Flower color | white, pink, green |
| Bloom period | May to September |
| Light | Full sun |
| Soil moisture | Dry, Average |
| USDA zones | 6-10 |
| Leaf arrangement | whorled |
| Leaf shape | narrow |
| Sap | Milky latex |
| Root system | Rhizomatous, spreads by root |
| Seed stratification | 30 days cold-moist |
| Monarch value (0-5) | 5 |
| Garden value (0-5) | 4 |
| Nectar value (0-5) | 4 |
| US states recorded | Arizona, California, Idaho, Nevada, Oregon, Utah, Washington |

## Identification

- 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.

## Ecology

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.

## Growing

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.

## 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.

## 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

- Plants of the World Online: https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:94272-1
- GBIF: https://www.gbif.org/species/3170291
- iNaturalist: https://www.inaturalist.org/taxa/56851
- Wikipedia: https://en.wikipedia.org/wiki/Asclepias_fascicularis
- BONAP county map: https://bonap.net/MapGallery/County/Asclepias%20fascicularis.png
- NatureServe: https://explorer.natureserve.org/Search?searchTerm=Asclepias%20fascicularis

## Photographs

- Asclepias fascicularis flowers 2003-06-05 (No machine-readable author provided. Curtis Clark assumed (based on copyright claims)., CC BY-SA 2.5): https://commons.wikimedia.org/wiki/File:Asclepias_fascicularis_flowers_2003-06-05.jpg
- Asclepias fascicularis, Narrowleaf Milkweed (glmory, CC0): https://commons.wikimedia.org/wiki/File:Asclepias_fascicularis,_Narrowleaf_Milkweed.jpg
- Narrowleaf Milkweed - Asclepias fascicularis (28595688567) (Björn S..., CC BY-SA 2.0): https://commons.wikimedia.org/wiki/File:Narrowleaf_Milkweed_-_Asclepias_fascicularis_(28595688567).jpg
- Narrowleaf Milkweed - Asclepias fascicularis (28595012917) (Björn S..., CC BY-SA 2.0): https://commons.wikimedia.org/wiki/File:Narrowleaf_Milkweed_-_Asclepias_fascicularis_(28595012917).jpg
- Narrowleaf Milkweed - Asclepias fascicularis (28595687447) (Björn S..., CC BY-SA 2.0): https://commons.wikimedia.org/wiki/File:Narrowleaf_Milkweed_-_Asclepias_fascicularis_(28595687447).jpg
- Narrowleaf Milkweed - Asclepias fascicularis (28595689207) (Björn S..., CC BY-SA 2.0): https://commons.wikimedia.org/wiki/File:Narrowleaf_Milkweed_-_Asclepias_fascicularis_(28595689207).jpg
- Narrowleaf Milkweed - Asclepias fascicularis (43433980632) (Björn S..., CC BY-SA 2.0): https://commons.wikimedia.org/wiki/File:Narrowleaf_Milkweed_-_Asclepias_fascicularis_(43433980632).jpg
- Narrowleaf Milkweed - Asclepias fascicularis (43436024432) (Björn S..., CC BY-SA 2.0): https://commons.wikimedia.org/wiki/File:Narrowleaf_Milkweed_-_Asclepias_fascicularis_(43436024432).jpg

## How to cite

Milkweed USA. (2026). Narrowleaf Milkweed (Asclepias fascicularis). https://milkweedusa.com/species/narrowleaf-milkweed/