How to grow petunia
Overview
Petunia is a tender herbaceous annual from the Solanaceae family, grown for its prolific, colourful trumpet-shaped flowers. It thrives in full sun and warm conditions, making it a staple for summer bedding, containers, and hanging baskets. Regular deadheading and feeding are essential to keep it blooming from spring through autumn.
Varieties
- Petunia 'Surfinia' — Trailing series ideal for hanging baskets and window boxes, very heat tolerant.
- Petunia 'Grandiflora' — Large-flowered, best for pots and borders; needs regular deadheading.
- Petunia 'Multiflora' — Compact, small-flowered, more weather-resistant than Grandiflora types.
- Petunia 'Wave' — Spreading ground-cover type, excellent for mass colour in beds.
Soil Preparation
Petunias prefer slightly acidic to neutral soil (pH 6.0–7.0) with good drainage. Improve heavy clay with compost or coarse sand. Add a slow-release fertiliser at planting time for steady nutrition.
Growing Guide
Plant petunias in a sunny, open position with well-drained soil. Space spreading types 30–40 cm apart, upright types 20–25 cm apart. Water at the base to avoid wetting foliage and reduce disease. In subtropical and tropical zones, plant in the cooler dry season for best results. Pinch back young plants to encourage branching and a fuller shape.
Sowing
Sow petunia seed on the surface of fine seed mix; do not cover as they need light to germinate. Germination takes 7–14 days at 21–24°C. Transplant seedlings when they have 4–6 true leaves, spacing as per growing notes. Direct sowing is not recommended in most gardens due to small seed size.
Care
Feed petunias every two weeks with a balanced liquid fertiliser (e.g., 10-10-10) during active growth. Pinch out spent flowers and trim leggy stems to just above a leaf node to encourage bushy rebloom. Reduce watering in late autumn to prevent root rot.
Companion Planting
Petunias pair well with alyssum, verbena, and lobelia for a continuous colour display. Avoid planting near potatoes or tomatoes to reduce risk of shared solanaceous diseases like potato virus Y.
Common Pests & Risks
Aphids, budworm (Helicoverpa), and spider mites are common on petunias in Australian gardens. Control aphids and mites with a strong water spray or horticultural oil; use Bacillus thuringiensis (Bt) for budworm. Remove affected flowers and foliage promptly to limit spread.
Troubleshooting
Yellow leaves: overwatering or nitrogen deficiency — reduce water, apply liquid feed. Leggy growth: insufficient light — move to full sun. Few flowers: too much shade or not deadheading — cut back stems and increase sun. Brown leaf edges: wind or salt burn — shelter from strong winds and avoid overhead watering. Sticky residue: aphid infestation — spray with neem oil.