Helianthus annuus 'Red Sun'

RHS Plant Profile
sunflower 'Red Sun'

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A fast-growing annual with broad, oval to heart-shaped, roughly hairy leaves. In summer, it bears huge singular flowers with velvety petals of dark bronze and deep dark centres. The flowers attract bees and the seeds that follow provide food for finches

Position

Full sun

Soil Types

Chalk, Clay, Loam, Sand

Max Height

1.5-2.5 metres

Max Spread

0.1-0.5 metres

Size

Time to Maturity
1 year
Max Spread
0.1-0.5 metres
Max Height
1.5-2.5 metres

Growing Conditions

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

Position

Full sun
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

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

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

How to Grow

Cultivation

Grow in moderately fertile, neutral to alkaline, humus-rich, moist but well-drained soil in full sun. This plant was included in the RHS Helianthus (sunflower) trial 2024 https://www.rhs.org.uk/plants/trials-awards/plant-trial-results/fleuroselect-sunflowers

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

  • Wildlife gardens
  • Cottage and informal garden
  • Flower borders and beds
  • Cut flowers
  • Wall side borders

Pruning

Cut back old stems after flowering as they die down for the winter

Pests

May be susceptible to slugs and snails

Diseases

May be susceptible to Powdery mildews and sclerotinia diseases