What do Japanese knotweed flowers look like?



August 11, 2022

With pure, dainty petals and heart-shaped leaves, you could be forgiven for thinking Japanese knotweed wasn’t the invasive pest it is. Thankfully, its flowers make it easy to identify. So, what do they look like?

Japanese knotweed creamy white flowers

Japanese knotweed flowers are tiny, five-pointed rounded stars usually white or cream in colour. They are so small they form part of a cluster which grow at the end of the stem. This cluster is long and thin and looks a little like a spike. You can usually spot Japanese knotweed flowers against the plant’s bright green leaves.

Creamy white flowers of Japanese knotweed

Long thin clusters of Japanese knotweed flowers

Japanese knotweed blossom

Flowers look like tiny five pointed, rounded stars

When does Japanese knotweed flower?

Japanese knotweed blooms from the end of August to the beginning of September in the UK. As a perennial, it will bloom year after year unless it is treated.

Did you know, the best time to treat Japanese knotweed is when it’s in full bloom? The weed “drinks” herbicides far better when there is more surface area to “swallow” the spray.

Plants mistaken for Japanese knotweed

When it flowers, Japanese knotweed is mistaken for a few other plants. Here are the most common:

  1. Bindweed - often confused for Japanese knotweed because its flowers are white. However, bindweed flowers are trumpet-shaped and large.
  2. Houttuynia - houttuyania cordata also has bold white petals, but also sports a central yellow spike. What's more, Japanese knotweed has no distinctive smell, whilst houttuynia smells like oranges! 
  3. Dogwood - produces white flower clusters in the summer, just as Japanese knotweed does. However, dogwood clusters are dome-shaped and the petals have sharper points!
Summer blossom of Japanese knotweed

Japanese knotweed stems full of flowers and seed heads

Japanese knotweed summer flowers

Large infestation of Japanese knotweed in bloom

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