Does it need staking?

It usually stays upright on its own, but may lean if grown in too much shade.

You can cut the stems back by half in early summer to encourage a bushier habit.

Plant guide

Smooth Blue Aster.

Symphyotrichum laeve

Pronounced sim-fih-oh-TRY-kum LEE-vee

Also known as Glaucous Aster, Glaucous Michaelmas-daisy, Smooth Aster, Smooth Blue Aster, Smooth-leaf Aster

The smooth blue aster is a lovely perennial that brings a splash of color to late summer and autumn gardens. It features smooth, hairless foliage and clusters of charming blue to violet flowers. This native plant is a favorite for pollinators looking for a late season nectar source.

At a glance

Care level: Easy
Plant type: Perennial
Light: Full sun
Indoor light: Direct sun
Water: Every 7 to 14 days
Mature size: 90 to 120 cm
Growth rate: Medium
Hardiness: USDA 3 to 8
Bloom time: Late summer to mid autumn

Care

Plant this aster in a spot with plenty of sun and well draining soil. Keep an eye out for powdery mildew if the air circulation is poor. Cut back the stems in late winter to encourage fresh spring growth.

Watering: Water regularly during the first growing season to establish a deep root system.
Feeding: A light application of compost in early spring is usually plenty.
Pruning: Cut back to the ground in late winter or very early spring.
Repotting: Divide the clumps every few years to maintain plant vigor.
Soil: Well draining loam or rocky soil
Soil pH: Neutral to slightly alkaline
Temperature: -35 to 30°C
Humidity: 40 to 70%
Drought tolerance: Moderate
Lifespan: Perennial, typically 5 to 10 years
Deer and rabbits: Moderate

Signs it needs repotting

Roots growing out of the drainage holes.
Water sitting on the surface for too long.
Plant growth slowing down significantly.

Safety

People: There is no known toxicity to humans, though it is not intended for consumption.
Pets: This plant is generally considered non toxic to cats and dogs.
Children: The plant is generally safe, but keep children from chewing on stems or leaves to prevent mild digestive upset.
Contact allergens: Handling the stems may cause mild skin irritation in sensitive individuals.
Airborne allergens: The pollen can trigger seasonal allergies in sensitive people during the late summer bloom.
Edibility: This plant is not considered edible and should not be consumed.

How to identify it

Smooth hairless blue green leaves
Clusters of violet blue daisy flowers
Yellow centers turning reddish purple
Sturdy upright branching stems

Height: 0.6 to 1.2m
Spread: 0.3 to 0.6m
Leaves: blue-green, glaucous, deciduous
Flowers: lavender, blue, violet, 2 to 3cm

Problems to watch for

AphidsCommon
Powdery MildewCommon
Aster YellowsUncommon
Leaf SpotUncommon
RustUncommon
Slugs and SnailsUncommon
Spider MitesRare

By symptom

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Growing it

Propagation: division, seed
When to plant: spring, autumn
Overwintering: Cut the dead stems back to the ground in late winter or early spring to tidy the garden. No special protection is needed as it is fully hardy.
In containers: It grows well in large containers, provided they have excellent drainage and at least 30 centimeters of depth.

Division

1. Dig up the clump in early spring.
2. Use a sharp spade to divide the root ball into smaller sections.
3. Replant the sections immediately at the same depth.

Pair with late blooming grasses to keep the garden looking tidy after the asters finish their display.

Grows well with

Goldenrod — The yellow flowers provide a classic color contrast with the blue aster.
Little Bluestem — This grass provides a sturdy backdrop and textural contrast.

Similar species

New England Aster — It has similar flowers but features hairy leaves and stems.

Science

Family: Asteraceae
Genus: Symphyotrichum
Order: Asterales
Class: Magnoliopsida
Native range: Central and eastern North America.
Conservation: It is secure across its native range and not currently of conservation concern.

It thrives in open woodlands and prairies where it competes for light by blooming after many other species have finished.

Value to wildlife: late season nectar source, supports native bee populations
Pollinators: bees, butterflies
Uses: pollinator gardens, prairie restoration, border plantings, cut flowers

Through the year

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Flowering

Fruiting

Foliage

Ecological indicators

Salinity: 2/9
Soil reaction: 6/9
Light: 7/9
Moisture: 4/9
Nutrients: 5/9
Temperature: 4/9

Taxonomy resolved against GBIF.

Questions people ask

Does it need staking?: It usually stays upright on its own, but may lean if grown in too much shade.
How do I prune it?: You can cut the stems back by half in early summer to encourage a bushier habit.

Where the name comes from

The name Symphyotrichum comes from Greek words meaning joined hair, while laeve refers to the smooth, hairless texture of the foliage.

Good to know

The species name laeve means smooth, referring to its hairless leaves.
It is a member of the sunflower family.
The flowers are a vital food source for migrating butterflies.

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This guide was generated with AI and checked against GBIF taxonomy. It is general information, not horticultural or veterinary advice. Read about how we build these guides.