Swamp milkweed Asclepias incarnata
Swamp milkweed (Asclepias incarnata) is a deciduous perennial flowering plant in the Apocynaceae family, native to Wet meadows and stream banks of eastern and central North America. It grows 90 cm–1.5 m (35 in–4.9 ft) tall and 50–90 cm (20–35 in) wide, wants full sun and high water, and is hardy to about -35 °C (-31 °F). Space plants about 60 cm (24 in) apart.
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Swamp milkweed at a glance
| Type | Perennial flowering plant, deciduous |
|---|---|
| Family | Apocynaceae |
| Mature height | 90 cm–1.5 m (35 in–4.9 ft) |
| Mature spread | 50–90 cm (20–35 in) |
| Spacing | 60 cm (24 in) centre to centre |
| Sun | Full sun, at least 6 h of direct sun a day |
| Water | High; drought tolerance low, waterlogging tolerance high |
| Soil pH | 5–8 |
| Cold hardiness | About -35 °C (-31 °F) once established (roughly USDA zone 3) |
| Heat stress | Likely above about 36 °C (97 °F) |
| Flowering | from about July for 4–7 weeks (northern hemisphere; later in cold climates, earlier in warm ones) |
| Wind tolerance | Low |
| Pollinator value | High |
| Edible | Not grown as food |
| Native to | Wet meadows and stream banks of eastern and central North America |
| Common in gardens of | 🇺🇸 United States, 🇨🇦 Canada |
Is Swamp milkweed toxic?
- People: moderately toxic
- Cats: moderately toxic
- Dogs: moderately toxic
- Parts: all parts, milky sap
Milkweeds contain cardenolides (heart poisons) that also protect monarch caterpillars; livestock and pets can be poisoned, and the sap irritates eyes.
If a child or pet may have eaten part of a plant, call a poison centre or vet straight away.
Companion planting: what to grow with Swamp milkweed
No well-documented helpful pairing. Group it with plants that like full sun and high water.
Questions about Swamp milkweed
- How far apart should I plant Swamp milkweed?
- About 60 cm (24 in) apart, centre to centre. A mature plant spreads 50–90 cm (20–35 in).
- Does Swamp milkweed need full sun?
- Full sun: at least 6 hours of direct sun a day.
- How much water does Swamp milkweed need?
- High water. Drought tolerance is low and waterlogging tolerance high.
- How cold-hardy is Swamp milkweed?
- It tolerates about -35 °C (-31 °F) once established, roughly USDA zone 3.
- When does Swamp milkweed flower?
- From about July for 4–7 weeks (northern hemisphere; later in cold climates, earlier in warm ones).
- Is Swamp milkweed poisonous to cats and dogs?
- For cats it is moderately toxic; for dogs moderately toxic; for people moderately toxic. Milkweeds contain cardenolides (heart poisons) that also protect monarch caterpillars; livestock and pets can be poisoned, and the sap irritates eyes.
- What grows well with Swamp milkweed?
- There is no well-documented companion pairing for Swamp milkweed. Group it with plants that like the same sun (full sun) and water (high).
Sources and evidence
Evidence grade A (A: strong evidence).
- Plants of the World Online (taxonomy, native range), Royal Botanic Gardens, Kew
- Missouri Botanical Garden Plant Finder, Missouri Botanical Garden
- Xerces Society pollinator conservation resources (regional plant lists and habitat guides), The Xerces Society for Invertebrate Conservation
Notes and assumptions
- Clusters of fragrant, pink, crown-shaped flowers in midsummer on tall stems, then upright pods of silky-tufted seeds. A clump-former that, unlike common milkweed, does not spread by roots, so it suits small gardens; monarch butterflies lay their eggs on it. Grows in wet or ordinary garden soil.
Reference values for planning, not horticultural, veterinary or medical advice. Varieties, soils and local climates differ: check with a local nursery or extension service.
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- Frangipani (plumeria) Plumeria rubra
- Butterfly weed Asclepias tuberosa
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- Star jasmine Trachelospermum jasminoides
- Mandevilla Mandevilla sanderi
- Lesser periwinkle Vinca minor
- Jelutong Dyera costulata