Helianthus annuus 'Giant Single'

RHS Plant Profile

sunflower 'Giant Single'

Annual Biennial

A tall and large, fast-growing annual with oval to heart-shaped, roughly hairy green leaves. In summer it produces a wonderfully large sunny yellow flower with a chocolate brown centre. Great for seeing who can grow the tallest and attracting bees and seeds that follow provide food for finches

Position

Full sun

Soil Types

Chalk, Clay, Loam, Sand

Max Height

2.5-4 metres

Max Spread

0.5-1 metres

Size

Time to Maturity: 1 year
Max Spread: 0.5-1 metres
Max Height: 2.5-4 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 a moderately fertile, humus-rich, moist but well-drained, neutral to alkaline soil in full sun. Will flower best in a long, hot summer. May need a cane to support the weight of the bloom and grow tall

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
City and courtyard gardens
Wildlife gardens
Flower borders and beds

Pruning

Cut back after flowering or once the flower heads have dried, then collect the seed or share them with the birds

Pests

May be susceptible to slugs and snails

Diseases

May be susceptible to powdery mildews and sclerotinia diseases