Dahlia 'Blue Boy' (D)

RHS Plant Profile
dahlia 'Blue Boy'

Save a plant

Where do you want to save Dahlia 'Blue Boy' (D)?

Plants I own
Wishlist
Go to My Plants
dahlia 'Blue Boy' visionspictures.com
dahlia 'Blue Boy' visionspictures.com
dahlia 'Blue Boy' visionspictures.com
Herbaceous Perennial
Thank you - your purchase supports our charity work Buy this from RHS Plants Shop
Buy online from £5.99Buy this from Plant Nurseries
6 Suppliers

A tuberous-rooted perennial to about 1m, with dark stems and mid-green foliage. Light blue-purple flowers, 15-20cm across, are a neat, rounded shape, and produced from mid-summer until the first frost

Position

Full sun

Soil Types

Clay, Loam, Sand

Max Height

0.5-1 metres

Max Spread

0.5-1 metres

Size

Time to Maturity
1 year
Max Spread
0.5-1 metres
Max Height
0.5-1 metres

Growing Conditions

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

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)
H3

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Asteraceae
Native to GB/Ireland
No
Foliage
Deciduous
Habit
Clump forming
Genus
Dahlia are tuberous rooted perennials with pinnately divided leaves and showy flowerheads, double in many cultivars, in summer and autumn
Name Status
Accepted
Horticultural Group

Horticultural Classification Codes

Horticultural Classification Codes are often given to genera which have a large number of species or cultivars. They are used to categorise cultivated plants based on specific, shared characteristics such as shape, colour, size or flowering time, and can be displayed as letters or numbers

For example:
Dahlia ‘Sunset Kate (Sin) = Single flower
Rosa ‘Marigold’ (HT) = Hybrid Tea

Decorative dahlias have fully double flowerheads with flat or slightly incurved florets

How to Grow

Cultivation

Grow in full sun, in fertile, humus-rich, well-drained soil enriched with organic matter and general-purpose fertiliser. Pinch out growing tips to encourage bushy plants. Water freely in dry periods. Lift and store tubers in autumn to replant, or use as a source of cuttings, in spring. See dahlia cultivation and our video How to plant dahlia tubers and care tips

Propagation

Propagate by softwood cuttings taken in spring from shoots from stored tubers, or divide the tubers, ensuring each section has at least one viable bud

Suggested planting locations and garden types

  • City and courtyard gardens
  • Cottage and informal garden
  • Patio and container plants
  • Cut flowers
  • Flower borders and beds
  • Bedding

Pruning

Deadhead to prolong flowering. Cut back to near ground level in autumn, once frost has damaged foliage, before lifting and storing for the winter

Pests

May be susceptible to aphids, capsid bugs, caterpillars, earwigs nibbling flowers, glasshouse red spider mite and slugs

Diseases

May be susceptible to powdery mildews in dry conditions, fungal rots including grey mould in wet conditions and in storage, and a virus that causes stunting, leaf markings and distortion