Dahlia 'Knockout'PBR (Sin)
dahlia 'Knockout'
A tuberous-rooted perennial to about 75cm, with very dark bronze, almost black, foliage, blooming from mid-summer until the first frosts. Single flowers have broad, lemon yellow petals, and a dark brown central disc opening to orange
Synonyms
Dahlia 'Mystic Ladies Knockout'Dahlia 'Mystic Knockout'
see moreDahlia Mystic Sun
Dahlia Mystic Illusion
_8814.JPG)
Size
Ultimate height
0.5–1 metresTime to ultimate height
1–2 yearsUltimate spread
0.5–1 metresGrowing conditions
Moisture
Moist but well–drained, Well–drainedpH
Acid, Alkaline, NeutralColour & scent
| Stem | Flower | Foliage | Fruit | |
| 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 Hardiness
H3Botanical details
- Family
- Asteraceae
- Native to GB / Ireland
- 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
Adopted
- 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
- Cottage and informal garden
- City and courtyard gardens
- Patio and container plants
- Wildlife gardens
- Cut flowers
- Flower borders and beds
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
Get involved
The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.