Swamp Milkweed care — light, water, toxicity and hardiness
Swamp Milkweed (Asclepias incarnata) wants full sun and a drink about every 3 days once established. It is hardy in USDA zones 3 to 9. It is toxic to pets — worth keeping out of reach.
| scientific name | Asclepias incarnata |
|---|---|
| family | Apocynaceae |
| category | flower |
| plant type | perennial |
| light | full sun |
| water cadence days | 3 |
| mature height cm | 120 |
| min zone | 3 |
| max zone | 9 |
| frost tolerant | true |
| toxic to pets | true |
| toxic to humans | true |
| edible | false |
How often should I water Swamp Milkweed?
Milkweed for wet spots; monarch host.
Who eats it
Palatable to grazing animals: low. Palatable to people: no. USDA records its toxicity as moderate.
What it needs
Its shade tolerance is high. Its moisture use is high. It wants at least about 15 inches of rain a year. Above roughly 65 inches of annual rain it struggles. It tolerates soil down to pH 5.0. It tolerates soil up to pH 8.0. Its fertility requirement is medium. Adapted to coarse, sandy soils: no. Adapted to medium, loamy soils: yes. Adapted to fine, clay soils: yes. Its tolerance of waterlogging is high. It needs at least 107 frost-free days. Its tolerance of chalky soil is medium. Its fire tolerance is low. Fire resistant: yes. It has been recorded down to -38°F. It suppresses neighbours chemically: no.
How it grows
It grows as a rhizomatous form. Its growth rate is moderate. Its lifespan is moderate. It puts on most of its growth in spring. It spreads by seed at a slow rate. It spreads vegetatively at a slow rate. It resprouts after damage: no. Coppices: no. At maturity it reaches about 4.9 feet. Its roots go down at least 18 inches. Its shape is erect. It holds its leaves through winter: no.
What it looks like
It blooms in fall. The flowers are red. Conspicuous in flower: yes. The foliage is green. The foliage texture is coarse. In summer the canopy is moderate in porosity. In winter it is porous in porosity. Fall colour: no. The fruit or seed is brown. Fruit begins in spring. Fruit finishes by fall. It fruits medium. The fruit persists on the plant: yes. The fruit is conspicuous: no.
Growing more of it
Propagated by seed: yes. Propagated by cuttings: no. Propagated by container: no. Propagated by bare root: no. Propagated by bulb: no. Propagated by corm: no. Propagated by tubers: no. Cold stratification required: no. Seedling vigour is low. Commercial availability: routinely available.
Source: Drafted from US Cooperative Extension horticulture guidance; pending HUMAN-05 review (issue 280) · ASPCA Toxic and Non-Toxic Plant List · 2026-09-02