Japanese Knotweed Identification and Removal

What is Japanese Knotweed?

Japanese Knotweed (Fallopia japonica) is a highly invasive plant species that poses a serious threat to properties and ecosystems across the UK. Originally introduced from East Asia as an ornamental plant in the 19th century, it has since become notorious for its rapid growth, resilience, and ability to cause structural damage. The plant grows in dense clumps with tall, hollow stems that resemble bamboo, and it features bright green, shield- or heart-shaped leaves arranged in a zig-zag pattern along the stem. During late summer, it produces clusters of small, creamy-white flowers, adding to its deceptive appearance as a harmless garden plant. However, the real danger lies underground, where an extensive root system known as rhizomes spreads laterally and vertically. These rhizomes can grow up to 3 metres deep and 7 metres wide, easily penetrating foundations, walls, patios, and drains. Japanese Knotweed spreads aggressively and can lie dormant for years before regrowing, making it difficult to control without specialist intervention. Due to its destructive nature, strict regulations govern its treatment and disposal, and early identification is essential to avoid legal, financial, and environmental complications.

• 1. Bamboo-like Hollow Stems

  • The plant has thick, hollow stems that resemble bamboo.

  • Stems grow in dense stands and can reach over 2–3 metres high in summer.

  • Reddish or purple speckles are often visible on young stems.

  2. Shield- or Heart-Shaped Leaves

  • Leaves are bright green, flat at the base and pointed at the tip.

  • Typically 10–15 cm long, growing in a distinctive zig-zag formation along the stem.

  • Leaf shape and growth pattern are strong identification clues.

  3. Red or Purple Shoots in Early Spring

  • New growth appears as asparagus-like red or purple shoots.

  • These emerge from the soil in March or April and grow rapidly.

  4. Clusters of Small White Flowers

  • Between August and October, creamy-white flowers bloom in dense panicles.

  • Each flower is small and delicate, adding a soft appearance to the plant.

  5. Thick, Woody Winter Canes

  • In colder months, stems die back and turn brittle and brown.

  • These dead canes can persist into winter and signal dormant rhizomes beneath.

  6. Orange/Brown Rhizomes

  • Rhizomes are the underground root structures that spread invasively.

  • When snapped, they reveal a bright orange or yellow interior.

  • Rhizomes can lie dormant and still regrow years later.

Winter

Japanese Knotweed does not enjoy the UK winter! After the first hard frost, the plant will loose its leaves and go into winter dormancy. The canes of Japanese Knotweed will continue to stand during winter but they will turn brown and become brittle.

Top Tip! – identifying Japanese knotweed is especially difficult in winter because of the lack of leaves and the canes looking ‘twig like’. You can also check the ground for fragments of old canes and also the crown of the plant for signs of growth areas!

Spring

Japanese Knotweed will start to grow as early as March in some places in the UK so it is important to be vigilant at all times of year! The growths will initially grow with triangular leaves and red stems. Sometimes they can look a little like asparagus!

Once the growths become more mature the leaves will ‘fill out’ and become less triangular and more ‘shield shape’ with a very flat base, smooth edges and a small tip. They will also lose their red colour and become a vibrant green, making Japanese knotweed identification much easier.

Early Summer

During summer, we have seen Japanese Knotweed grow upto 1 foot a week! The main canes of growth are primarily green with small red/purple specks on them. The stems that come off the main cane grow in a left/right zig/zag pattern. When identifying Japanese knotweed, remember the leaves are shield shape with a flat base, smooth edge and slight tip to the end of the leaf.

Late Summer

As the summer progresses and your Japanese Knotweed continues to grow taller and taller, it will get to a point where it stops growing in height and starts to flower in long creamy clusters. The flowering is designed for seed creation and dispersal but thankfully the seeds are not viable in the UK!

Many UK plants share visual traits with Japanese Knotweed, which can lead to confusion. Be cautious not to confuse it with:

• Dogwood: Similar stem colour but different leaf formation.

• Himalayan Balsam: Taller plant with pink flowers and shallower roots.

• Bindweed: Twisting growth habit and heart-shaped leaves but soft stems.

• Russian Vine: Rapid climber with similar flowers but distinct stem behaviour.

If you’re unsure, it’s always safer to consult a professional.

Failure to correctly identify Japanese Knotweed early can lead to:

• Exponential spread of the plant across gardens or building sites

• Legal complaints from neighbours under the Anti-social Behaviour Act

• Mortgage lenders declining loans on affected properties

• Increased removal costs due to mature rhizome networks

Even if you suspect Japanese Knotweed but aren’t certain, acting early will save you time and money.