What is Japanese knotweed?

Japanese Knotweed Growth Cycle

Japanese knotweed is among the biggest challenges for today’s homeowners. As it is a highly invasive weed, which can spread very quickly from only a small fragment, and cause extensive damage to property and displace native species of flora.

Japanese knotweed is a tall, vigorous ornamental plant that escaped from cultivation in the late nineteenth century to become an aggressive invader in the urban and rural environment.

What Is Japanese Knotweed? Identification and Characteristics

Japanese knotweed (Fallopia japonica), a member of the dock family (Polygonaceae), is one of the most aggressive and invasive plant species in the UK. Known for its rapid growth and ability to spread underground, it poses a serious threat to buildings, infrastructure, and native biodiversity.

Key Features of Japanese Knotweed

  • Growth Habit: Japanese knotweed is a rhizomatous perennial, meaning it spreads via underground stems known as rhizomes. These allow the plant to regenerate and spread quickly.
  • Stems: Its hollow, bamboo-like stems are green with distinctive purple speckles and can grow to heights of 2 to 3 metres. The stems grow in dense clumps and form a zig-zag pattern as they arch outward.
  • Leaves: Mature leaves are up to 12cm (120mm) in length, with a flattened base and pointed tip. They are arranged alternately along the stem in a characteristic zig-zag formation.
  • Flowers: Japanese knotweed blooms late in the season, typically between August and October. It produces small, creamy-white flowers that hang in clusters from the leaf axils—the point where the leaf connects to the stem.
  • Rhizome System: Below ground, the rhizomes are thick, woody, and knotty in appearance. When snapped, they reveal a bright orange core. These underground structures can reach depths of at least 2 metres and spread horizontally up to 5 metres from the parent plant.

Why Accurate Identification Matters

Identifying Japanese knotweed early is critical for effective control and legal compliance. The plant’s invasive rhizome system allows it to spread rapidly, even from small fragments, and it is capable of causing structural damage to buildings, paving, and drainage systems.

If you suspect you have Japanese knotweed on your property, it’s essential to consult with a PCA-accredited specialist like Japanese Knotweed Elimination Ltd to assess the risk and begin professional treatment.

Seasonal Growth Cycle of Japanese Knotweed

Japanese knotweed undergoes a distinct seasonal growth pattern, which plays a key role in its rapid spread and resilience.

  • Winter Dormancy: During the winter months, the plant’s leaves die back, revealing woody, orange-brown stems. These stems can remain standing for several years and contribute to the build-up of dense plant litter as they decompose slowly, enriching the soil and suppressing native vegetation.
  • Spring Regrowth: Between March and April, new Japanese knotweed shoots emerge, often appearing as red or purple spears with rolled-back leaves. These shoots are fuelled by the energy stored in the plant’s extensive underground rhizome system.
  • Rapid Growth: Once sprouted, Japanese knotweed can grow at an alarming rate. Growth rates of up to 40mm per day have been recorded, making early detection and treatment essential to prevent widespread infestation.

Understanding the seasonal life cycle of Japanese knotweed is vital for effective identification and treatment. If you notice signs of regrowth in spring, it’s important to act quickly—contact Japanese Knotweed Elimination Ltd for expert survey and control services across South Wales.

Japanese Knotweed die back winter

Flexible Payment Options Available

We offer 0% APR Monthly Payments or

You can split the cost over a number of years*

  • 07582 869979