BattenBlooms
PL. —Symphyotrichum subspicatumBotanical illustration — drop image
Symphyotrichum subspicatum

Douglas Aster

SummerFall
5a–9bHardiness zone
Peak bloom windowZone 6b · frost-offset weeks
Winter
Not in bloom
Spring
In bloom
Summer
Peak bloom
Fall
Not in bloom
Peak bloom
In bloom
Background

Douglas aster is a perennial wildflower native to western North America, ranging from Alaska south to California and east into the Rocky Mountain foothills. It grows 18 to 48 inches tall and produces violet ray florets around yellow-to-red disk florets from midsummer into fall, making it one of the latest-blooming natives in its range.

It grows naturally along stream banks, coastal bluffs, and moist forest edges but adapts to average garden soils with consistent moisture. Plants spread gradually by rhizomes and self-seed freely; in smaller gardens, removing spent heads after bloom limits unwanted spread. Cutting plants back by half in early summer reduces flopping without significantly delaying the bloom period. A 2–3 inch mulch layer helps retain soil moisture and moderates root temperature in the warmer parts of its range.

Douglas aster is a critical late-season foraging resource for native bees, including oligolectic specialists in the tribe Astereae, as well as for migrating monarch butterflies. Seed heads left standing through fall and winter provide food for finches and sparrows.

Good companions
GoldenrodYarrowPurple ConeflowerCalifornia Fuchsia
Care guide
SunFull sun to part shade
WaterModerate
SoilMoist, well-drained, loamy
Spacing18–24 in
Height16–48 in
Zone5a – 9b
Native RegionAK, CA, ID, MT, OR, WA, WY
Frost hardy
Seasonal tasks
spring
sowDivide established clumps every 2–3 years in early spring as new shoots emerge; replant vigorous outer sections and discard the woody central core.
sowStart seeds indoors 6–8 weeks before last frost; press seeds onto the surface of moist seed-starting mix without covering — they need light to germinate.
sowTransplant seedlings outdoors after last frost, spacing 18–24 inches apart in a moist site with at least a half day of direct sun.
summer
cutCut stems back by one-third to one-half in early summer to encourage a bushier, more self-supporting habit and reduce flopping later in the season.
watchMonitor for leafhoppers from midsummer onward — they vector aster yellows, which causes distorted stems and yellowed foliage. There is no cure; remove and destroy affected plants immediately.
watchCheck lower foliage for powdery mildew in late summer, particularly where air circulation is poor. Thin crowded stems to improve airflow and avoid overhead watering.
fall
cutCut plants to within 3–4 inches of the ground after the first hard frost, or leave stems standing through winter to supply seed for birds.
Common problems

Aster Yellows

Symptoms

Deformed, greenish flowers, stunted growth, and yellowed foliage. Flower centers may produce tufts of leafy growth instead of normal petals.

Treatment

No cure. Remove and destroy infected plants immediately to stop spread. Control leafhoppers, which transmit the disease, and remove nearby weed hosts.

Powdery mildew

Symptoms

White or grey powdery coating on leaves — usually starting on older growth in humid conditions or when nights cool.

Treatment

Improve air circulation by thinning plants. Apply neem oil or potassium bicarbonate spray at first sign. Avoid overhead watering.

Rust

Symptoms

Orange to brown raised pustules on the undersides of leaves, with yellow spotting on the upper surface. Heavy infections cause leaves to yellow and drop.

Treatment

Remove and destroy infected leaves. Avoid overhead watering and improve air circulation. Apply a sulfur or copper-based fungicide if it spreads. Clear plant debris in fall.