How to Grow Zinnia
Zinnia elegans
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.
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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.
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 | 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.
Care Guide
- Feeding
- Balanced liquid feed fortnightly once flowering starts.
- Watch for
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- Powdery mildew
- Aphids
- Leaf spot
- Grey mould
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.
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