How to Grow Zinnia
Zinnia elegans
Zinnias are heat-loving, half-hardy annuals for full sun and well-drained soil. Direct sow after frost or start indoors and transplant carefully; they dislike root disturbance and cold. Space well and water at the base to prevent mildew—good airflow is essential. Avoid rich feeding; too much nitrogen makes lush, floppy plants. Deadhead or cut stems regularly to keep flowers coming. For cutting, harvest when blooms are fully open and stems pass the “wiggle test” (heads don’t flop).
When to Start
Start seeds indoors 4 weeks before your last frost date. Transplant outdoors once night temperatures stay above 8°C and soil has warmed to at least 10°C.
Don't know your frost date? Find it here →
Growth Stages
Approximate days from start
Care Essentials
- Balanced liquid feed fortnightly once flowering starts.
- Excellent cut flowers. Need full sun and good airflow to prevent mildew. Don't overhead water.
Growing Conditions
- Min. soil temperature
- 10°C+
- Germination temperature
- 20–25°C
Pet Safety
- Sow indoors
- —
- Transplant out
- —
- First harvest
- —
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Spacing & Planting
| Plant spacing | 30 cm |
| Row spacing | 40 cm |
| Sow depth | 0.5 cm |
| Mature height | 75 cm |
| Mature spread | 30 cm |
For taller varieties (e.g., 'Benary's Giant'). Good air circulation helps prevent powdery mildew. Dwarf varieties can be spaced at 20 cm.
Pests & Diseases
Pest Aphids
Identification: Clusters of green or black insects on growing tips and flower buds; sticky honeydew; distorted growth
- Blast off with a jet of water
- Spray with insecticidal soap
- Encourage ladybirds, lacewings, and hoverflies
- Spray with a contact insecticide containing pyrethrins
Pest Slugs and Snails
Identification: Seedlings eaten at ground level; ragged holes in young leaves; slime trails around plants
- Apply organic slug pellets (ferric phosphate based) around newly planted seedlings
- Hand-pick at dusk; use beer traps
- Protect individual plants with cut plastic bottles as cloches
- Apply ferric phosphate slug pellets around vulnerable plants
Pest Earwigs
Identification: Ragged, chewed petals, particularly on outer florets; damage appears overnight; earwigs found hiding in flower heads during the day
- Set traps using upturned pots stuffed with straw on canes near plants — check and empty daily
- Shake flower heads over a bucket in the morning to dislodge earwigs
- Keep garden tidy to reduce hiding places
- Earwig traps are more effective than sprays; chemical control is rarely necessary
Disease Powdery Mildew Golovinomyces cichoracearum
Symptoms: White, powdery coating on leaves and stems; leaves yellow, curl, and die back; flowering declines
Treatment: Remove badly affected leaves; spray with a sulphur-based fungicide or potassium bicarbonate solution
Prevention: Space plants widely for good airflow; water at the base; avoid overhead watering; choose mildew-resistant varieties
Disease Alternaria Leaf Spot Alternaria zinniae
Symptoms: Small, dark brown spots with concentric rings on leaves; spots may merge; leaves yellow and drop; flowers may also be affected
Treatment: Remove affected leaves; improve air circulation; spray with a copper-based fungicide
Prevention: Space plants well; water at the base; avoid overhead watering; clear plant debris at end of season; rotate planting positions
Disease Grey Mould (Botrytis) Botrytis cinerea
Symptoms: Fuzzy grey mould on flowers, stems, and leaves; brown, water-soaked patches; flowers rot before fully opening
Treatment: Remove affected plant parts promptly; improve air circulation
Prevention: Space plants well; water at the base; deadhead regularly; avoid wetting foliage in the evening
Growing Conditions
| Min. soil temperature | 10°C |
| Germination temperature | 20–25°C |
| Base growth temperature | 8°C |
| Min. daylength to start | 10.5h |
| Photoperiod sensitivity | day neutral |
Frequently Asked Questions
- How far apart should I plant Zinnia?
- Plant Zinnia 30cm apart with 40cm between rows.
- When does Zinnia flower?
- Zinnia typically flowers approximately 50 days after transplanting.
- Is Zinnia frost hardy?
- Zinnia is classified as Tender.
