Smooth blue aster Symphyotrichum laeve
Smooth blue aster (Symphyotrichum laeve) is a deciduous perennial flowering plant in the Asteraceae family, native to Prairies and open woods of most of North America. It grows 60 cm–1.2 m (24 in–3.9 ft) tall and 40–60 cm (16–24 in) wide, wants full sun and low water, and is hardy to about -38 °C (-36 °F). Space plants about 45 cm (18 in) apart.
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Smooth blue aster at a glance
| Type | Perennial flowering plant, deciduous |
|---|---|
| Family | Asteraceae |
| Mature height | 60 cm–1.2 m (24 in–3.9 ft) |
| Mature spread | 40–60 cm (16–24 in) |
| Spacing | 45 cm (18 in) centre to centre |
| Sun | Full sun, at least 6 h of direct sun a day |
| Water | Low; drought tolerance moderate, waterlogging tolerance none |
| Soil pH | 5.5–8 |
| Cold hardiness | About -38 °C (-36 °F) once established (roughly USDA zone 3) |
| Heat stress | Likely above about 34 °C (93 °F) |
| Flowering | from about September 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 | Prairies and open woods of most of North America |
| Common in gardens of | 🇺🇸 United States, 🇨🇦 Canada, 🇬🇧 United Kingdom, 🇩🇪 Germany |
Is Smooth blue aster toxic?
- People: not known to be toxic
- Cats: not known to be toxic
- Dogs: not known to be toxic
Not known to be poisonous.
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 Smooth blue aster
No well-documented helpful pairing. Group it with plants that like full sun and low water.
Questions about Smooth blue aster
- How far apart should I plant Smooth blue aster?
- About 45 cm (18 in) apart, centre to centre. A mature plant spreads 40–60 cm (16–24 in).
- Does Smooth blue aster need full sun?
- Full sun: at least 6 hours of direct sun a day.
- How much water does Smooth blue aster need?
- Low water. Drought tolerance is moderate and waterlogging tolerance none.
- How cold-hardy is Smooth blue aster?
- It tolerates about -38 °C (-36 °F) once established, roughly USDA zone 3.
- When does Smooth blue aster flower?
- From about September for 4–7 weeks (northern hemisphere; later in cold climates, earlier in warm ones).
- Is Smooth blue aster poisonous to cats and dogs?
- For cats it is not known to be toxic; for dogs not known to be toxic; for people not known to be toxic. Not known to be poisonous.
- What grows well with Smooth blue aster?
- There is no well-documented companion pairing for Smooth blue aster. 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
- Illinois Wildflowers (descriptions and insect-visitor records), John Hilty, illinoiswildflowers.info
Notes and assumptions
- A tallgrass prairie plant: deep roots make it drought-proof once established; it wants sun and lean soil (rich soil makes it flop). Leave the stems standing in winter for seed-eating birds and overwintering insects.
- Smooth, waxy blue-green leaves clasping the stems and sprays of clear sky-blue daisies with yellow centres in autumn, resistant to the mildew that troubles other asters. Late nectar for migrating monarchs and bumblebee queens.
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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