Dahlia imperialis (Tree dahlia)

Botanical name

Dahlia imperialis

Other names

Tree dahlia, Giant dahlia, Imperial dahlia, Bell tree dahlia, Dahlia maximiliana, Dahlia maxonii, Dahlia arborea, Dahlia lehmannii

Genus

Dahlia Dahlia

Species

D. imperialis - D. imperialis is an upright, vigorous, herbaceous perennial with brittle, cane-like stems bearing large pinnate, wrinkled, toothed, mid- to dark green leaves and loose panicles of lavender to mauve flowers from autumn into winter.

Foliage

Deciduous

Habit

Upright, Clump-forming

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Colour

Flower

Lavender, Mauve in Autumn; Mauve, Lavender in Winter

Foliage

Dark-green in Spring

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How to care

Watch out for

Specific pests

Glasshouse red spider mite , Earwigs , Caterpillars , Capsid bug , Aphids , Leaf-mining sawflies , Slugs

Diseases

May also be susceptible to viruses and fungal rots.

Specific diseases

Powdery mildew , Grey mould

General care

Pruning

Do not disbud. Cut to the base in late winter. Can be cut by half in summer to encourage branching. Mulch after cutting in summer.

Propagation

Take stem cuttings in late winter. Cut stem sections so that each piece contains a node. Plant in moist compost with nodes pointing up. Cover with approximately 3cm of compost. Keep compost moist.

Propagation methods

Stem segments, Seed

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Monthly care advice

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Where to grow

Dahlia imperialis (Tree dahlia) will reach a height of 5m and a spread of 3m after 1-2 years.

Suggested uses

Flower Arranging, Cottage/Informal, Containers, City, Beds and borders

Cultivation

Grow in moist but well-drained or well-drained soil in sun. May bloom in colder areas if last frost date is delayed significantly. Mulch in mid-autumn.

Soil type

Clay, Loamy, Sandy

Soil drainage

Well-drained, Moist but well-drained

Soil pH

Acid, Neutral

Light

Full Sun

Aspect

South, West

Exposure

Sheltered

UK hardiness Note: We are working to update our ratings. Thanks for your patience.

Tender in frost (H3)

USDA zones

Zone 10, Zone 9, Zone 8

Defra's Risk register #1

Plant name

Dahlia imperialis (Tree dahlia)

Common pest name

Corn borer; Corn moth; European corn borer; European maize borer; European stalk borer; Maize pyralid

Scientific pest name

Ostrinia nubilalis

Type

Insect

Current status in UK

Present (Limited)

Likelihood to spread in UK (1 is very low - 5 is very high)

3

Impact (1 is very low - 5 is very high)

3

General biosecurity comments

Polyphagous boring pest present in the UK since the 1930’s. A maize-affecting race was detected for the first time in 2010. Industry may wish to monitor for its presence and mitigate against impacts.

Defra's Risk register #2

Plant name

Dahlia imperialis (Tree dahlia)

Common pest name

Rice leaf nematode; Strawberry crimp disease nematode; White tip nematode; White tip nematode of rice

Scientific pest name

Aphelenchoides besseyi

Type

Nematode

Current status in UK

Absent

Likelihood to spread to UK (1 is very low - 5 is very high)

2

Impact (1 is very low - 5 is very high)

3

General biosecurity comments

Damaging nematode affecting rice crops and strawberry production in warmer climates; could potentially present a threat to strawberry production and ornamental production in protected environments. But modern production practices seem to reduce likelihood of impacts. Pest is also regulated at EU level; which reduces likelihood of entry.

Defra's Risk register #3

Plant name

Dahlia imperialis (Tree dahlia)

Common pest name

Necrotic spot

Scientific pest name

Impatiens necrotic spot virus

Type

Virus or Viroid

Current status in UK

Present (Widespread)

Likelihood to spread in UK (1 is very low - 5 is very high)

2

Impact (1 is very low - 5 is very high)

3

General biosecurity comments

Pest of mainly ornamentals and vegetables; present in the UK; and covered by the EU listing of Tomato Spotted Wilt Virus. To be kept under consideration in light of a review of the EU listing.

About this section

Our plants are under greater threat than ever before. There is increasing movement of plants and other material traded from an increasing variety of sources. This increases the chances of exotic pests arriving with imported goods and travellers, as well as by natural means. Shoot is working with Defra to help members to do their part in preventing the introduction and spread of invasive risks.

Traveling or importing plants? Please read "Don't risk it" advice here

Suspected outbreak? Click here for contact details to report to the relevant authority.

Date updated: 7^th March 2019 For more information visit: https://planthealthportal.defra.gov.uk/