Common milkweed Asclepias syriaca
Common milkweed (Asclepias syriaca) is a deciduous perennial flowering plant in the Apocynaceae family, native to Fields, roadsides and prairies of eastern and central North America. It grows 90 cm–1.8 m (35 in–5.9 ft) tall and 60 cm–1.5 m (24 in–4.9 ft) wide, wants full sun and low water, and is hardy to about -38 °C (-36 °F). Space plants about 80 cm (31 in) apart.
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Common milkweed at a glance
| Type | Perennial flowering plant, deciduous |
|---|---|
| Family | Apocynaceae |
| Mature height | 90 cm–1.8 m (35 in–5.9 ft) |
| Mature spread | 60 cm–1.5 m (24 in–4.9 ft) |
| Spacing | 80 cm (31 in) centre to centre |
| Sun | Full sun, at least 6 h of direct sun a day |
| Water | Low; drought tolerance high, waterlogging tolerance none |
| Soil pH | 5–8 |
| Cold hardiness | About -38 °C (-36 °F) once established (roughly USDA zone 3) |
| Heat stress | Likely above about 38 °C (100 °F) |
| Flowering | from about June for 4–6 weeks (northern hemisphere; later in cold climates, earlier in warm ones) |
| Wind tolerance | Moderate |
| Pollinator value | High |
| Edible | Not grown as food |
| Native to | Fields, roadsides and prairies of eastern and central North America |
| Common in gardens of | 🇺🇸 United States, 🇨🇦 Canada |
| Invasive in | parts of central and eastern Europe (naturalised and spreading): check local rules before planting |
Is Common 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 Common milkweed
No well-documented helpful pairing. Group it with plants that like full sun and low water.
Questions about Common milkweed
- How far apart should I plant Common milkweed?
- About 80 cm (31 in) apart, centre to centre. A mature plant spreads 60 cm–1.5 m (24 in–4.9 ft).
- Does Common milkweed need full sun?
- Full sun: at least 6 hours of direct sun a day.
- How much water does Common milkweed need?
- Low water. Drought tolerance is high and waterlogging tolerance none.
- How cold-hardy is Common milkweed?
- It tolerates about -38 °C (-36 °F) once established, roughly USDA zone 3.
- When does Common milkweed flower?
- From about June for 4–6 weeks (northern hemisphere; later in cold climates, earlier in warm ones).
- Is Common 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 Common milkweed?
- There is no well-documented companion pairing for Common milkweed. Group it with plants that like the same sun (full sun) and water (low).
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
- Broad grey-green leaves, balls of sweet-scented dusty-pink flowers that perfume a meadow in early summer, and warty pods full of silky floss. The single most important host plant of the monarch butterfly in eastern North America. Spreads strongly by underground runners: better for meadows than small borders.
Reference values for planning, not horticultural, veterinary or medical advice. Varieties, soils and local climates differ: check with a local nursery or extension service.
Related plants
- Oleander Nerium oleander
- Frangipani (plumeria) Plumeria rubra
- Butterfly weed Asclepias tuberosa
- Madagascar periwinkle Catharanthus roseus
- Star jasmine Trachelospermum jasminoides
- Mandevilla Mandevilla sanderi
- Lesser periwinkle Vinca minor
- Jelutong Dyera costulata