How to Grow Petunias
Petunia × hybrida
Petunias are tender annuals that need full sun, regular feeding, and deadheading for continuous summer colour. Sow seed indoors in February-March on the surface of fine compost — they need light to germinate. Plant out after the last frost. Feed containers weekly with high-potash liquid fertiliser and deadhead spent blooms regularly. Cut back leggy stems by half in midsummer to rejuvenate. Trailing types are superb for hanging baskets and window boxes.
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.
Don't know your frost date? Find it here →
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.
Growing Conditions
- Min. soil temperature
- 18°C+
- Germination temperature
- 21–25°C
Pet Safety
- Sow indoors
- —
- Transplant out
- —
- 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.
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.
