How to Grow Dahlia
Dahlia pinnata
Dahlias are frost-tender, tuberous perennials for full sun, fertile, well-drained soil, and regular water. Start tubers in pots under cover in spring and plant out after frost. Stake tall varieties at planting; tie in as they grow. Pinch the tips to encourage branching and more blooms. Deadhead to keep flowers coming until frost. In cold climates, lift and store tubers after blackening frost; in milder areas, mulch deeply to overwinter in ground.
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.
Don't know your frost date? Find it here →
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.
Growing Conditions
- Min. soil temperature
- 10°C+
- Germination temperature
- 18–24°C
Pet Safety
- Direct sow
- —
- 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.
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.
