How to grow aster
Overview
Aster (Symphyotrichum novi-belgii) is a late-flowering perennial grown for its daisy-like blooms in shades of purple, pink, and blue. It thrives in full sun and well-drained soil, providing garden colour from late summer through autumn.
Varieties
- Symphyotrichum novi-belgii 'Purple Dome' — Compact, mounding habit with deep purple flowers, ideal for borders in Australian gardens.
- Symphyotrichum novi-belgii 'Alma Potschke' — Tall, vibrant pink blooms that attract pollinators, suited to mixed perennial beds.
- Symphyotrichum novi-belgii 'White Ladies' — Pure white flowers, excellent for cutting and adding contrast in autumn gardens.
Soil Preparation
Aster prefers well-drained, loamy soil with a pH of 6.0–7.0. Enrich with compost or well-rotted manure before planting. Ensure good drainage to prevent root rot in wet conditions.
Growing Guide
Plant aster in full sun with well-drained, moderately fertile soil. Space clumps 30–45 cm apart. Water regularly to keep soil evenly moist, especially during dry spells. Mulch to retain moisture and suppress weeds. Divide clumps every 2–3 years in early spring to maintain vigour and prevent overcrowding.
Sowing
Sow seeds 3 mm deep in seed trays or directly in garden beds after frost risk has passed. Germination takes 10–14 days at 18–22°C. Transplant seedlings when they reach 5–10 cm tall, spacing 30–45 cm apart.
Care
Feed with a balanced slow-release fertiliser in early spring and again after flowering. Cut spent stems back to the base in late winter to encourage fresh growth. Divide clumps every 2–3 years to maintain vigour and prevent disease.
Companion Planting
Good companions include echinacea, rudbeckia, and sedum, which share similar sun and moisture needs. Avoid planting near aggressive spreaders like mint or bamboo, which can compete for space and nutrients.
Common Pests & Risks
Watch for powdery mildew in humid or crowded conditions; improve air circulation and avoid overhead watering. Aphids may appear on new growth; treat with a strong spray of water or insecticidal soap if needed.
Harvesting
Cut flowers when they are partly open, with the centre still tight, for longest vase life. Harvest in the early morning and place stems immediately in water. Deadhead regularly to extend bloom time.
Troubleshooting
Yellow leaves: overwatering or poor drainage; reduce water and improve soil. Brown leaf edges: underwatering or hot, dry winds; increase watering and mulch. Powdery mildew: poor air circulation or high humidity; space plants and avoid overhead watering. Stunted growth: nutrient deficiency; feed with balanced fertiliser in spring. Leggy stems: too much shade; move to full sun.