How to Grow Dahlia
Bulb
Dahlias are generous, theatrical summer flowers, available in simple bee-friendly singles as well as neat pompoms, waterlily forms and dinner-plate blooms. They grow from tender tubers and will flower for months when given sun, rich soil and regular attention. Their range of colours makes them invaluable for lively borders, pots and cutting gardens.
Planting
Start tubers under cover in March or April in pots of free-draining compost, then harden them off before planting outside after the last spring frost. Alternatively, plant tubers directly into warm soil from late April or May in milder areas, later in colder districts and Scotland. Set each tuber about 10 to 15 cm deep with its stem or growing point uppermost. Space according to eventual size, usually 45 to 90 cm, and install sturdy stakes at planting time.
Care
Water deeply during dry weather and mulch the soil to retain moisture. Feed plants regularly through the growing season, following the fertiliser label, and deadhead faded blooms to keep new buds coming. Tie growth to stakes as stems lengthen. Check young shoots for slugs and earwigs, removing pests by hand where practical. Choose open-centred single varieties from RHS Plants for Pollinators for greater wildlife value.
Bloom time
Dahlias normally flower from July until the first autumn frosts, often lasting into October in sheltered southern gardens. In northern gardens and Scotland they may start slightly later. Regular deadheading and picking encourages a continuous display through late summer and early autumn.
Garden uses
Dahlias are superb focal plants for sunny borders and make generous cut flowers for the house. Tall cultivars bring structure to the back of a border, while compact forms fill patio pots. Mix flower shapes for texture, or repeat one colour for a calmer scheme. Open-centred varieties are especially useful where pollinator-friendly planting is a priority.
Tips
After frost blackens the foliage, cut stems back and lift tubers in cold or wet areas. Dry them briefly, then store frost-free in barely damp compost, sand or wood fibre. In mild, well-drained gardens, tubers can remain outdoors beneath a thick mulch. Label every plant before lifting, as dormant tubers are easily confused.
Growing Dahlia: frequently asked questions
How do I grow dahlia in the UK?
Start tubers under cover in March or April in pots of free-draining compost, then harden them off before planting outside after the last spring frost.
When does dahlia flower?
Dahlias normally flower from July until the first autumn frosts, often lasting into October in sheltered southern gardens.
How do I care for dahlia?
Water deeply during dry weather and mulch the soil to retain moisture.
General guidance for UK gardens. Timing and hardiness vary by region and season; the RHS or a local garden centre can advise for your area. Page updated 18 Sep 2026.