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BeddingHerbaceous PerennialSynonym

Dahlia Mystic Illusion
  • RHS AGM
  • RHS Plants for pollinators

dahlia 'Knockout'

'Knockout' is a bushy, clump-forming, tuberous perennial to 80cm in height with toothed, pinnate, dark mahogany to purple-black leaves. Single to semi-double, bright yellow flowers with orange centres are borne from summer to autumn

Synonyms
Dahlia 'Mystic Ladies Knockout'
Dahlia 'Mystic Knockout'
see moreDahlia Mystic Sun
Dahlia Mystic Illusion

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Size
Ultimate height
0.5–1 metres
Time to ultimate height
1–2 years
Ultimate spread
0.5–1 metres
Growing conditions
Clay
Loam
Sand
Moisture
Moist but well–drained, Well–drained
pH
Acid, Alkaline, Neutral
Colour & scent
StemFlowerFoliageFruit
Spring Black Purple
Summer Yellow Black Purple
Autumn Yellow Black Purple
Winter
Position
  • Full sun
Aspect

South–facing or East–facing or West–facing

Exposure
Sheltered
Drought resistance
Yes
Hardiness
H3
Botanical details
Family
Asteraceae
Native to the UK
No
Foliage
Deciduous
Habit
Bushy
Potentially harmful
All parts may cause severe discomfort if ingested and may irritate skin. Wear gloves and other protective equipment when handling
Genus

Dahlia are tuberous rooted perennials with pinnately divided leaves and showy flowerheads, double in many cultivars, in summer and autumn

Name status

Not established

Horticultural Group
Single-flowered dahlias have flowerheads usually less than 10cm across, with one or two rows of spreading ray florets, surrounding a central boss of small tubular disc florets which are valuable for bees and butterflies

How to grow

Cultivation

Grow in fertile, humus-rich, well-drained soil, enriched with organic matter and general purpose fertiliser, in full sun. Pinch out growing tips to encourage bushy plants and stake (see staking perennials). Water freely in dry periods. Lift and store tubers in autumn to replant or use as a source of cuttings in spring

Propagation

Propagate by softwood cuttings taken in spring from shoots from stored tubers, or divide the tubers ensuring each division has a viable bud

Suggested planting locations and garden types
  • Architectural
  • Cottage and informal garden
  • City and courtyard gardens
  • Patio and container plants
  • Cut flowers
  • Flower borders and beds
  • Wall side borders
Pruning

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

Pests

Leaf miners, aphids, glasshouse red spider mite and slugs are common pests. Earwigs sometimes damage blooms. Capsid bug and caterpillars are occasional pests

Diseases

Powdery mildews can be damaging in dry conditions. In wet weather grey moulds and other fungal rots can be a problem. Fungal rots can also damage stored tubers. A virus may cause stunting, leaf markings and distortion

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