When should I plant dahlia tubers outside in the UK?

Plant outdoors from mid-April to mid-May in most of England. In northern England and Scotland, wait until late May or early June. The soil temperature should be at least 10C and all frost risk must have passed. Tubers planted into cold, wet soil may rot before they sprout.

Can I plant dahlias in March?

Only indoors in pots, never directly outside. Start tubers in 2-litre pots of multipurpose compost on a bright windowsill or in an unheated greenhouse from early March. This gives a 4-6 week head start. The plants can go outdoors once all frost risk has passed, usually late May.

How deep should I plant dahlia tubers?

Plant tubers 10-15cm deep with the old stem pointing upward. Deeper planting protects the growing point from late frosts. In heavy clay soil, plant 10cm deep and add a handful of grit beneath the tuber to prevent waterlogging and rot during wet spring weather.

Do dahlias come back every year in the UK?

Dahlias are perennial but not frost-hardy in most of the UK. Lift tubers after the first autumn frost, dry them, and store at 5-10C over winter. In sheltered gardens in south-west England and mild coastal areas, tubers can survive in the ground under a 15cm mulch layer.

How far apart should I plant dahlias?

Space depends on the variety's mature size. Dwarf bedding types need 30-45cm. Medium decorative and ball types need 45-60cm. Tall decorative and dinnerplate varieties need 60-90cm. Closer spacing gives a fuller display but increases disease risk from poor air circulation.

When do dahlias start flowering?

Dahlias flower from mid-July to the first hard frost. Tubers started indoors in March flower from late June. Outdoor-planted tubers from May flower from mid to late July. Deadheading spent blooms every few days extends the flowering season by directing energy into new buds.

Should I soak dahlia tubers before planting?

Soaking is not necessary and risks encouraging rot. If tubers look very shrivelled after winter storage, place them on damp compost for 48 hours to rehydrate. Do not submerge them in water. Healthy, firm tubers can go straight into pots or the ground without any soaking.

Growing | 30 November 2025 | 13 min read

When to Plant Dahlias in the UK

Month-by-month guide to planting dahlias in the UK. Covers starting tubers indoors, planting out dates by region, and variety selection for UK gardens.

Colourful dahlia blooms in a cutting garden with decorative cactus and pompon varieties

Growing

Plant dahlia tubers outdoors in the UK from mid-April to mid-May after the last frost. Starting tubers indoors from March gives a 4-6 week head start. Dahlias are not frost-hardy. Space tubers 45-90cm apart and plant 10-15cm deep. With fortnightly high-potash feeding, dahlias flower continuously from July to the first hard frost.

Outdoor PlantingMid-April to mid-May after last frost

Indoor Head StartStart March for flowers 4-6 weeks earlier

Spacing45-90cm apart, 10-15cm deep

Flowering PeriodJuly to first hard frost

Key takeaways

Plant tubers outdoors mid-April to mid-May after the last frost has passed in your area
Start tubers indoors in pots from March for flowers 4-6 weeks earlier than outdoor-planted tubers
Dahlias are killed by frost so never plant out before your region's last frost date
Plant 10-15cm deep and 45-90cm apart depending on the variety's mature size
Feed fortnightly with high-potash fertiliser from first bud formation for continuous flowering
Lift tubers after the first autumn frost and store at 5-10C in a frost-free place over winter

dahlias tubers flowers summer flowers planting times cut flowers

By Garden UK Editorial Team

Our team produces practical UK gardening guidance from source research, contributor records and established horticultural practice. Editorial standards are overseen by Matt W.

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