Helianthus giganteus

RHS Plant Profile
giant sunflower

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Herbaceous Perennial
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A clump-forming perennial, up to 2.5m in height, with narrow, coarse green leaves and small flowers in late summer and early autumn, with dark yellow centres and yellow ray florets on dark reddish to green stems

Position

Full sun, Partial shade

Soil Types

Chalk, Loam, Sand, Clay

Max Height

2.5-4 metres

Max Spread

1-1.5 metres

Size

Time to Maturity
1–2 years
Max Spread
1-1.5 metres
Max Height
2.5-4 metres

Growing Conditions

Chalk Loam Sand Clay
Moisture
Moist but well–drained or Well–drained
pH
Neutral or Alkaline

Position

Full sun Partial shade
Aspect
South–facing or West–facing
Exposure
Sheltered
Hardiness

Hardiness Ratings

All ratings refer to the UK growing conditions unless otherwise stated. Minimum temperature ranges (in degrees C) are shown in brackets

  • H1A: under glass all year (>15C)
  • H1B: can be grown outside in the summer (10 - 15)
  • H1C: can be grown outside in the summer (5 - 10)
  • H2: tolerant of low temperatures, but not surviving being frozen (1 to 5)
  • H3: hardy in coastal and relatively mild parts of the UK (-5 to 1)
  • H4: hardy through most of the UK (-10 to -5)
  • H5: hardy in most places throughout the UK even in severe winters (-15 to -10)
  • H6: hardy in all of UK and northern Europe (-20 to -15)
  • H7: hardy in the severest European continental climates (< -20)
H4

RHS Recommended: for People & Planet

RHS Recommended Plants for People & Planet

For Water Resilience

Plants for Flood Resilience

Plants that can help manage heavy rain by catching rainfall, slowing surface run-off, encouraging water into the soil or taking it up through their roots, contributing to flood resilient gardens.

Plants for both Wet and Dry Conditions

Plants that cope with changing soil moisture, including wet winters and extended summer dry. Once established, they grow as wet and dry conditions alternate.

For Temperature Resilience

Plants for Temperature Cooling

Plants that cool air temperature by providing shade, transpiration, or reflection to reduce heat impact on people, animals, soil or other ground surface.

Plants for Wind Shelter

Plants with dense canopies often grown as a tall thick hedge or grouping can block wind and shelter gardens, buildings and people.

For Carbon Storage

Plants for Carbon Storage

Plants that can take up carbon (CO₂) through photosynthesis and store it within the plant or deposit it by their roots into the soil.

For Biodiversity

Plants for Pollinators

Plants that have flowering properties (pollen and/or nectar) that are particularly beneficial for pollinating insects such as bees, butterflies and hoverflies.

Growing conditions for maximum benefit

This plant will provide the maximum benefits if it is healthy and allowed to grow to maturity

For Bio-Diversity

  • Plants for Pollinators

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Asteraceae
Native to GB/Ireland
No
Foliage
Deciduous
Habit
Spreading branched, Clump forming
Genus
Helianthus can be tall, erect annuals, tuberous or rhizomatous perennials, with coarse simple leaves and large daisy-like flower-heads
Name Status
Correct

How to Grow

Cultivation

Grow in a moderately fertile, humus-rich, moist, well-drained, neutral to alkaline soil in full sun. May need support. See staking perennials

Propagation

Propagate by seed or division. Divide established clumps every 2-4 years to both increase plants and retain vigour. See sowing seeds indoors for further advice

Suggested planting locations and garden types

  • Cottage and informal garden
  • Wildlife gardens
  • Coastal
  • Wildflower meadow
  • Prairie planting
  • Cut flowers
  • Flower borders and beds
  • Wall side borders

Pruning

deadhead to prolong flowering

Pests

May be susceptible to slugs and snails

Diseases

May be susceptible to Powdery mildews and sclerotinia diseases