Troubleshooting
Smooth Blue Aster problems — and how to fix them
Smooth Blue Aster (Symphyotrichum laeve) is generally forgiving once you match its basics, but a few issues come up again and again. Here is what each one looks like, why it happens, and the fix.
Lodging in rich soil
Though usually self-supporting, overly fertile or shaded plants can lean. Grow lean and sunny, or pinch stems in early summer to keep them compact.
Occasional powdery mildew
More resistant than other asters, but crowded, damp conditions can still cause it. Maintain airflow and avoid wetting foliage to keep the smooth leaves clean.
Aphids on new growth
Soft new shoots and buds can attract aphids. Hose them off or tolerate them, as beneficial insects usually keep colonies in check on a healthy plant.
Self-seeding
Can spread by seed into nearby beds. Deadhead spent flowers if you want to limit volunteer seedlings, or leave seed heads standing for birds and winter interest.
Prevent smooth blue aster problems before they start
Most smooth blue aster issues are care-mismatch, not bad luck. Dial in the basics:
Looking for smooth blue aster in general rather than its problems? Read the full smooth blue aster care guide — light, water, soil and feeding.
Smooth Blue Aster problems — FAQ
Why is my smooth blue aster lodging in rich soil?
Though usually self-supporting, overly fertile or shaded plants can lean. Grow lean and sunny, or pinch stems in early summer to keep them compact.
Why is my smooth blue aster occasional powdery mildew?
More resistant than other asters, but crowded, damp conditions can still cause it. Maintain airflow and avoid wetting foliage to keep the smooth leaves clean.
Why is my smooth blue aster aphids on new growth?
Soft new shoots and buds can attract aphids. Hose them off or tolerate them, as beneficial insects usually keep colonies in check on a healthy plant.
Why is my smooth blue aster self-seeding?
Can spread by seed into nearby beds. Deadhead spent flowers if you want to limit volunteer seedlings, or leave seed heads standing for birds and winter interest.