About
A tall, vigorous herbaceous perennial to 2.1m high, with cane-like stems flecked with purple, and shovel-shaped leaves borne alternately (in a zig-zag pattern) along the stems. Produces tassels of white flowers in late summer and early autumn. This plant is considered invasive, and legal requirements apply to its control.
About the genus
Reynoutria is a diverse genus of plants that may be annual, perennial, or woody. Species are cultivated for their flowers, foliage, or architectural habit and are adapted to various climatic conditions
Growing conditions
SunlightFull sun, Partial shade
Soil typeChalk, Clay, Loam, Sand
Soil pHAcid, Alkaline, Neutral
Soil moistureMoist but well-drained, Well-drained, Poorly-drained
AspectEast-facing, North-facing, South-facing, West-facing
ExposureExposed, Sheltered
UK hardinessH7
Plant details
Plant typeHerbaceous Perennial
HabitColumnar upright
FoliageDeciduous
Height1.5-2.5 metres
Spread2.5-4 metres
Time to full height1 year
Suggested usesBorders, containers, mixed plantings.
Care notes
CultivationJapanese knotweed can grow in a wide range of situations spreading rapidly, even from small fragments, through vigorous, fast-growing rhizomes. This plant is listed on Schedule 9 of the UK Wildlife & Countryside Act as an invasive non-native species. Although not banned from sale, it is an offence to plant or cause it to grow in the wild IN ENGLAND, WALES, NORTHERN IRELAND and the REPUBLIC OF IRELAND. Gardeners possessing it should undertake measures to control it. See Japanese knotweed, and RHS advice on invasive non-native species, for further information
PruningMinimal pruning required. Remove dead or damaged growth as needed.
PropagationPlease see cultivation notes
Pest resistanceMay be susceptible to Aphalara itadori psyllids but generally pest free
Disease resistanceMay be susceptible to leafspot but generally disease-free