Helianthus annuus 'Hallo'

RHS Plant Profile
sunflower 'Hallo'

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sunflower 'Hallo' RHS
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Annual Biennial

A clump-forming hardy annual with a branching habit and green foliage producing large golden double yellow flowers with dark brown centres in the summer through until the autumn

Position

Full sun

Soil Types

Chalk, Clay, Loam

Max Height

1-1.5 metres

Max Spread

0.1-0.5 metres

Size

Time to Maturity
2–5 years
Max Spread
0.1-0.5 metres
Max Height
1-1.5 metres

Growing Conditions

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

Position

Full sun
Aspect
East–facing or 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)
H5

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Asteraceae
Native to GB/Ireland
No
Foliage
Deciduous
Habit
Bushy, 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
Accepted

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

  • City and courtyard gardens
  • Cottage and informal garden
  • Prairie planting
  • Wildlife gardens
  • Cut flowers
  • Flower borders and beds

Pruning

Cut back after flowering

Pests

May be susceptible to slugs and snails

Diseases

May be susceptible to powdery mildews and sclerotinia diseases