How to Grow Dahlia
Dahlia pinnata
When to Start
Best started from plugs, corms, or slips. Pot up indoors 7 weeks before last frost, then plant out once soil reaches 10°C.
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Growth Stages
Approximate days from start
Care Essentials
- High-potash liquid feed fortnightly once buds form.
- Pinching out tips and regular deadheading are key to a long display. Stake tall varieties.
Companion Planting
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Growing Conditions
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- Direct sow
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- First harvest
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Spacing & Planting
| Plant spacing | 60 cm |
| Row spacing | 75 cm |
| Sow depth | 0.5 cm |
| Mature height | 100 cm |
| Mature spread | 60 cm |
For medium to large decorative varieties which require staking. Smaller bedding dahlias can be planted 30-40 cm apart.
Care Guide
- Feeding
- High-potash liquid feed fortnightly once buds form.
- Watch for
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- Slugs
- Earwigs
- Aphids
- Powdery mildew
Pests & Diseases
Pest Slugs and Snails
Identification: Young shoots eaten to ground level or with large irregular holes; slime trails on and around plants
- Apply organic slug pellets (ferric phosphate) around emerging shoots
- Use beer traps or copper tape barriers
- Encourage hedgehogs, frogs and ground beetles
- Ferric phosphate-based pellets
Pest Earwigs
Identification: Ragged, irregular holes chewed in petals, mainly overnight. Earwigs hide inside flower heads during the day
- Trap in upturned pots stuffed with straw or newspaper, placed on canes among plants
- Shake flower heads over a sheet to dislodge and remove
- No chemical controls currently available for home gardeners
Pest Aphids
Identification: Clusters of small green or black insects on shoot tips and flower buds, causing distorted growth
- Squash by hand or blast off with a water jet
- Spray with fatty acid-based insecticide
- Encourage ladybirds, lacewings and hoverflies
- Spray with a contact insecticide containing deltamethrin
Disease Powdery Mildew
Symptoms: White powdery coating on leaves, causing yellowing and premature leaf drop
Treatment: Remove badly affected leaves. Spray with a fungicide approved for ornamentals if severe
Prevention: Space plants well for good airflow, water at soil level, and avoid drought stress
Disease Dahlia Smut Entyloma dahliae
Symptoms: Circular pale spots on leaves that develop dark brown spore masses in the centre
Treatment: Remove and destroy affected leaves. Improve air circulation around plants
Prevention: Avoid overhead watering, space plants well, and clear up fallen debris at the end of the season
Disease Grey Mould (Botrytis) Botrytis cinerea
Symptoms: Fuzzy grey mould on flowers, stems and tubers, often starting on damaged or dying tissue
Treatment: Remove and destroy affected parts promptly. Ensure good ventilation around plants
Prevention: Avoid overcrowding, remove spent flowers promptly, and ensure tubers are thoroughly dried before winter storage
Growing Conditions
| Min. soil temperature | 10°C |
| Germination temperature | 18–24°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 Dahlia?
- Plant Dahlia 60cm apart with 75cm between rows.
- When does Dahlia flower?
- Dahlia typically flowers approximately 80 days after transplanting.
- Is Dahlia frost hardy?
- Dahlia is classified as Tender.
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