UK plant library · perennial

Dahlia

Dahlia (hybrids) · Asteraceae

Showy blooms from summer to autumn; a huge revival in popularity

Photo: W. Bulach, CC BY-SA 4.0, via Wikimedia Commons

Sun: Full sun
Soil: Fertile, well-drained
Soil pH: Acid to neutral; also tolerates alkaline soil. Fertile, moist but well-drained soil matters more
Water: Water well in dry spells
Hardiness: Half-hardy/tender, RHS H3. In most of the UK, lift and store tubers frost-free over winter
Height and spread: 30cm-1.8m tall depending on cultivar (about 1m typical); spread 30-90cm

Guv's tipDeadhead dahlias to boost flowering and keep an eye out for slugs and snails. Hand-picking at night works a treat.

Through the year

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Sow or plant

In flower

Timings are for the UK as a whole. Northern and exposed gardens often run a couple of weeks later.

When to plant

Start tubers indoors Mar-Apr. Plant tubers outdoors mid-late Apr to May, and potted or growing plants after the last frost, late May-early Jun

Flowering

Jul to the first frosts (Oct-Nov); some from Jun

Pruning

Deadhead to boost flowering; pinch out tips

Making more plants

Cuttings, division of tubers, seed

Watch out for

Pest

Slugs and snails

Look for: Irregular holes in leaves, slime trails, seedlings eaten

What to do: Hand-pick at night, barriers, beer traps, encourage predators; ferric phosphate pellets sparingly

Pest

Aphids

Look for: Colonies of small green/black insects on shoot tips, sticky honeydew, distorted leaves

What to do: Squash or wash off, encourage ladybirds and other predators; insecticidal soap if severe

Pest

Capsid bugs

Look for: Small ragged holes in young leaves, distorted flowers

What to do: Usually tolerated; clear debris in winter

Pest

Earwigs

Look for: Ragged holes in petals and leaves

What to do: Straw-stuffed pot traps

Disease

Powdery mildew

Various (Erysiphales)

Look for: White powdery coating on leaves

What to do: Water in dry spells, mulch, improve air flow, resistant cultivars

Always read and follow the label on any treatment, and check it is approved for use where you live.

Safety and spread

Pets and people: Mildly toxic: listed as toxic to dogs, cats and horses by the ASPCA, with mild stomach upset and dermatitis. Low severity; tubers and foliage can irritate skin

Weed risk: Not listed as an invasive plant in Great Britain

Checked against two or more reputable gardening sources. How we check our facts

Keep it by the back door

The Plant Doctor and the Guv's book

Printable pest and disease charts with real photographs, and all 50 UK plants in one book.

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