Helianthus giganteus (Giant sunflower)

Botanical name

Helianthus giganteus

Other names

Giant sunflower, Tall sunflower, Helianthus alienus, Helianthus borealis, Helianthus subtuberosus, Helianthus validus

Genus

Helianthus Helianthus

Species

H. giganteus - H. giganteus is a vigorous, upright, deciduous perennial with lance-shaped, dark green leaves and branching, reddish-purple stems bearing hairy, elliptic to lance-shaped, mid-green leaves and loose clusters of bright yellow flowers in summer.

Native to

Canada, Eastern United States

Foliage

Deciduous

Habit

Upright, Clump-forming

---

Colour

Flower

Bright-yellow in Summer

Foliage

Mid-green in Spring; Mid-green in Summer; Mid-green in Autumn

---

How to care

Watch out for

Specific pests

Slugs , Snails

Specific diseases

Powdery mildew , Sclerotinia diseases

General care

Pruning

Cut back after flowering.

Propagation

Divide every 2-4 years to maintain vigour.

Propagation methods

Division, Seed

---

Monthly care advice

---

Where to grow

Helianthus giganteus (Giant sunflower) will reach a height of 3.5m and a spread of 1.5m after 1-2 years.

Suggested uses

Add to salads, Architectural, Beds and borders, Containers, Cottage/Informal, Flower Arranging, Wildflower

Cultivation

Grow in moderately fertile, humus-rich, moist but well-drained soil in full sun. Needs long, hot summers to flower well. May need support. Mulch annually with garden compost or well-rotted manure. Site carefully as may be invasive

Soil type

Chalky, Clay, Loamy

Soil drainage

Moist but well-drained

Soil pH

Alkaline, Neutral

Light

Full Sun

Aspect

South, East, West

Exposure

Sheltered

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

Hardy (H4)

USDA zones

Zone 9, Zone 8, Zone 7, Zone 6, Zone 5, Zone 4

Defra's Risk register #1

Plant name

Helianthus giganteus (Giant sunflower)

Common pest name

African cottom leafworm; Cotton leafworm; Egyptian cotton leafworm; Egyptian cotton worm; Mediterranean climbing cutworm; Meditteranea Brocade; Tobacco cutworm

Scientific pest name

Spodoptera littoralis

Type

Insect

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

Regulated pest; frequently intercepted with occasional outbreaks which have been successfully eradicated in the UK.

Defra's Risk register #2

Plant name

Helianthus giganteus (Giant sunflower)

Common pest name

American serpentine leaf miner; chrysanthemum leaf miner

Scientific pest name

Liriomyza trifolii

Type

Insect

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

Regulated pest already subject to review at the EU level (2013). Regularly intercepted in the trade.

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/