Aster Care: Growing Fall-Blooming Stars
Asters light up the late summer and fall garden with their cheerful, daisy-like flowers, providing a vital nectar source for migrating butterflies and late-season bees. Blooming primarily in shades of purple, blue, pink, and white, often with yellow centers, they bring welcome color when many other perennials are fading. While generally easy to grow, some taller varieties benefit from pinching earlier in the season, and attention to air circulation helps prevent powdery mildew.
(Botanical Note: Many North American asters formerly in the Aster genus have been reclassified into other genera like Symphyotrichum, Eurybia, and Ionactis. However, they are all still commonly referred to as Asters.)
Common Types of Garden Asters
There's a wide variety of asters suitable for gardens:
New England Aster (Symphyotrichum novae-angliae)
- Tall (3-6 ft), upright; profuse blooms (purple, pink, magenta); full sun, average/moist soil. Prone to lower leaf mildew; benefits from pinching. Hardy Zones 4-8.
- Examples include: 'Purple Dome' (compact), 'Alma Pötschke' (pink), 'Hella Lacy' (purple).
New York Aster (Symphyotrichum novi-belgii)
- Similar height (2-5 ft); flowers blue, lavender, pink, white. Prefers full sun, consistent moisture. Susceptible to mildew (choose resistant cultivars). Hardy Zones 4-8.
- Examples include: 'Professor Anton Kippenberg' (dwarf blue), 'Alert' (compact pink).
Aromatic Aster (Symphyotrichum oblongifolium)
- Bushy (1-3 ft); lavender-blue flowers cover plant; fragrant foliage. Tolerant of drier conditions; excellent mildew resistance. Hardy Zones 3-8.
- Examples include: 'October Skies', 'Raydon's Favorite'.
Other Notable Asters
- Wood Asters (Eurybia divaricata, S. cordifolium): Shade-tolerant; small white/pale blue flowers.
- Heath Aster (S. ericoides): Fine foliage; clouds of tiny white flowers; dry tolerant; spreads.
- Calico Aster (S. lateriflorum): Small white flowers, changing center; arching stems. 'Lady in Black' has dark foliage.
Planting Asters
Most asters are easy to establish in the right location.
When to Plant
- Spring or Fall: Good times for planting.
Ideal Growing Conditions
- Light: Full sun (6+ hours) strongly preferred for most (except Wood Asters). Best flowering, sturdy stems, less mildew.
- Soil: Adaptable to average, well-draining soil. NE/NY types prefer moisture; Aromatic/Heath tolerate drier. Avoid waterlogged soil.
- Spacing: Space 1-3 feet apart. Crucial: Provide good air circulation by not overcrowding, especially for taller types prone to mildew.
Planting Technique
Select location with adequate sun and air circulation. Match soil moisture preference.
Loosen soil. Amend with compost if very poor or needs moisture (for NE/NY types). Ensure good drainage.
Dig hole slightly wider/same depth as root ball.
Gently remove from pot. Place in hole level with surrounding soil.
Fill hole, firm gently. Water thoroughly.
Watering Asters
- Water regularly until established.
- Provide consistent moisture for NE/NY Asters, especially pre-bloom/bloom. Drought stress increases mildew risk.
- Aromatic, Heath types more drought-tolerant once established.
- Water at base.
Fertilizing Asters
- Generally light feeders. Light compost or balanced fertilizer in spring usually sufficient. Avoid excessive nitrogen (causes weak stems).
Maintenance and Care
Pinching (for Tall Varieties)
- Pinch back stems of tall types by 1/3-1/2 in late spring/early summer (before early July). Encourages bushiness, prevents flopping, increases flowers. Snip top few inches.
Division (Important for Vigor)
- Divide every 2-4 years (spring preferred) to maintain vigor, prevent overcrowding (improves air circulation), control spread. Dig clump, discard old center, replant healthy outer sections.
Deadheading
- Generally not necessary. Leave seed heads for birds/winter interest.large-**
Cleanup
- Cut back dead stems late fall or early spring. Fall cleanup helps reduce disease spores.
Troubleshooting Common Problems
Powdery mildew is the most common concern.
Powdery Mildew
Symptoms and Management
White powdery coating on leaves/stems. Thrives in humidity/poor circulation.
- Prevention: Resistant cultivars (Aromatic Aster!), full sun, air circulation (spacing, division, pinching), water at base.
- Control: Remove affected leaves. Fungicides if severe, but cultural controls are key.
Rust / Leaf Spots
Symptoms and Management
- Other fungal diseases causing orange pustules or spots.
- Prevention/Control: Similar cultural controls as for mildew. Remove affected leaves.
Flopping / Leggy Growth
Possible Causes and Solutions
- Insufficient Sun: Needs full sun.
- Overly Rich Soil / Too Much Fertilizer: Causes weak stems.
- Lack of Pinching (Tall Varieties): Pinch early summer.
- Overcrowding: Divide regularly.
Conclusion
Asters are essential perennials for extending garden color into fall and supporting late-season pollinators. By choosing appropriate varieties, providing full sun and good air circulation, pinching taller types, and dividing regularly, you can enjoy their spectacular autumn display. Prioritize mildew-resistant types for lower maintenance.
