Science · Plants, Natives & Crops
Narrowleaf Milkweed
Western native milkweed with narrow whorled leaves; a monarch larval host that normally dies back seasonally.
Asclepias fascicularis · Dormant-season herbaceous perennial
Profile
- Light
- Full sun
- Growth
- Spreads by rhizomes and windborne seed
- Ecology
- Monarch caterpillars eat foliage; avoid insecticides on host plants
- Safety
- Milky latex is irritating and plant tissue is toxic if eaten
Water & soil targets
- Moisture (VWC)
- Site-calibrated; depends on soil texture
- Salinity tolerance
- Not reliably characterized for this catalog label; avoid saline irrigation and diagnose with soil/water testing.
- Drought tolerance
- Good when established; occasional water sustains active-season foliage.
Optimal root measurement depth
3–8 in
Shallow fibrous or rhizomatous roots. Typical guidance; confirm with a soil probe on site.
Keep young plants moderately moist, then water intermittently with drainage. Reduce irrigation when dormant; bare stems or seasonal dieback alone do not imply drought injury.
Problems to watch
- Oleander aphids
- Root rot in waterlogged soil
- Pesticide exposure harming caterpillars
Stress signs
- Distorted sticky new growth
- Blackened soft crown
- Wilt during active growth rather than normal dormancy
Where you'll find it
- Monarch host planting
- Native pollinator meadow
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All Science profilesGeneral agronomic guidance and typical ranges; actual targets vary by site, soil, climate and season.