How to Grow Petunias
Petunia × hybrida
When to Start
Start seeds indoors 11 weeks before your last frost date. Transplant outdoors once night temperatures stay above 10°C and soil has warmed to at least 18°C.
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Growth Stages
Approximate days from start
Care Essentials
- High-potash liquid feed weekly for container plants. Fortnightly in borders.
- Surfinia and trailing types are best for baskets and containers. Deadheading is essential for continuous flowering.
Companion Planting
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Growing Conditions
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- Sow indoors
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- Transplant out
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- First harvest
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Spacing & Planting
| Plant spacing | 30 cm |
| Row spacing | 30 cm |
| Sow depth | 0 cm |
| Mature height | 30 cm |
| Mature spread | 40 cm |
Popular annual flower. Slow starter from seed - start indoors 10-12 weeks before last frost.
Care Guide
- Feeding
- High-potash liquid feed weekly for container plants. Fortnightly in borders.
- Watch for
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- Aphids
- Slugs
- Petunia bud rot
- Tobacco mosaic virus
Pests & Diseases
Pest Aphids
Identification: Clusters of small green or black insects on shoot tips, flower buds, and undersides of leaves; sticky honeydew and distorted growth
- Squash small colonies by hand or blast off with a jet of water
- Spray with insecticidal soap or neem oil, covering undersides of leaves
- Encourage ladybirds, lacewings, and hoverflies as natural predators
- Spray with a systemic insecticide containing acetamiprid (e.g., Bug Clear Ultra)
Pest Slugs and Snails
Identification: Irregular holes chewed in leaves and petals, slime trails on foliage and around containers
- Apply organic slug pellets (ferric phosphate based)
- Use copper tape around containers
- Set beer traps or hand-pick at dusk
- Apply slug pellets containing ferric phosphate around plants
Pest Caterpillars (Budworm)
Identification: Holes bored into flower buds that fail to open, frass (droppings) visible inside damaged buds, ragged petals
- Hand-pick caterpillars and check inside buds regularly
- Spray with Bacillus thuringiensis (Bt) biological insecticide
- Spray with pyrethrin-based insecticide targeting caterpillars
Disease Botrytis (Grey Mould) Botrytis cinerea
Symptoms: Fuzzy grey mould on spent flowers, stems, and leaves; brown, water-soaked patches that spread in wet weather
Treatment: Remove affected flowers and foliage promptly; improve air circulation; avoid overhead watering
Prevention: Deadhead regularly; space plants for airflow; water at the base; avoid wetting foliage in the evening
Disease Tobacco Mosaic Virus Tobacco mosaic virus
Symptoms: Mottled yellow and green patterns on leaves, stunted growth, distorted flowers with colour-breaking streaks
Treatment: No cure — remove and destroy infected plants immediately to prevent spread
Prevention: Buy virus-free plants; wash hands and tools between plants; do not smoke near petunias as the virus can transfer from tobacco
Disease Petunia Bud Rot
Symptoms: Flower buds turn brown and mushy before opening, often with a slimy texture; buds may drop prematurely
Treatment: Remove affected buds; improve ventilation around plants; reduce overhead watering
Prevention: Ensure good air circulation; avoid overcrowding in containers; water at the base in the morning
Growing Conditions
| Min. soil temperature | 18°C |
| Germination temperature | 21–25°C |
| Photoperiod sensitivity | day neutral |
Frequently Asked Questions
- How far apart should I plant Petunias?
- Plant Petunias 30cm apart with 30cm between rows.
- When does Petunias flower?
- Petunias typically flowers approximately 65 days after transplanting.
- Is Petunias frost hardy?
- Petunias is classified as Tender.
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