Does it need staking?

It usually stands up well on its own, but pinching it back in early summer can encourage a bushier, sturdier habit.

How much sun does it need?

It thrives in full sun to light shade.

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
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: -34 to 35°C
Humidity: 30 to 60%
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 of the soil for too long.
The plant stops producing new growth during the season.

Safety

People: There are no reports of significant toxicity to humans, but it is not intended for consumption.
Pets: This plant is generally considered non toxic to cats and dogs.
Children: While not poisonous, the stems can be somewhat stiff, so keep an eye on small children to prevent accidental scratches.
Contact allergens: Some individuals may experience mild skin irritation from handling the foliage.
Airborne allergens: The pollen can trigger seasonal allergies in sensitive individuals 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: 0.45 to 0.9m
Leaves: blue green, deciduous
Flowers: blue, violet, 2 to 4cm

Common problems

Powdery mildew — A white fungal growth appears on leaves when air circulation is poor.
Rust — Small orange or brown spots develop on the undersides of leaves.

Growing it

Propagation: division, seed
When to plant: spring, autumn
Overwintering: Cut the stems back to the ground after the foliage dies back in late autumn. It is fully hardy and requires no special protection.
In containers: It grows well in large containers, provided they have excellent drainage and at least 3 gallons of soil volume.

Division

Dig up the clump in early spring as new growth appears.
Use a sharp spade to divide the root ball into smaller sections.
Replant the divisions immediately at the same depth as the original plant.

Pair this aster with other late blooming prairie plants to create a continuous nectar supply for pollinators.

Grows well with

Goldenrod — The yellow flowers of goldenrod provide a beautiful color contrast to the blue aster blooms.
Little Bluestem — This grass provides a lovely structural backdrop for the aster.

Keep away from

Similar species

New England Aster — It has rougher, hairy leaves compared to the smooth foliage of this species.

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 naturally occurs in open woodlands and prairies where it competes for light in late summer.

Value to wildlife: late season nectar source, pollinator magnet
Pollinators: bees, butterflies, moths
Uses: pollinator garden, prairie restoration, late season color

Through the year

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Flowering

Fruiting

Foliage

Ecological indicators

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

Taxonomy resolved against GBIF.

Questions people ask

Does it need staking?: It usually stands up well on its own, but pinching it back in early summer can encourage a bushier, sturdier habit.
How much sun does it need?: It thrives in full sun to light shade.

Where the name comes from

The name Symphyotrichum comes from Greek words meaning joined hair, referring to the pappus bristles, while laeve means smooth, describing its hairless leaves.

Good to know

The leaves have a smooth, waxy coating that gives them a blue green appearance.
It is a favorite food source for many native bee species before winter.
The flowers can range from deep blue to light lavender.

Is your smooth blue aster looking unwell?

This page is a general guide. Pocket Botanist diagnoses problems from a photo of your actual plant, works out watering for your light and conditions, and reminds you when care is due.

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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.