How to identify Japanese knotweed: Three signs to look for in your garden this summer

Timelapse shows alarming rate Japanese Knotweed grows at

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Japanese knotweed can be a headache for property owners and gardeners alike, so it is important to catch it early before it gets out of hand. As this invasive weed reaches its peak growing period, it will be easier to spot in the cracks and crevices of your garden – but what exactly are you looking for? These are the key signs that you have Japanese knotweed growing on your property.

When is the best time to find Japanese knotweed?

The best time to identify Japanese knotweed is mid to late summer, when the plant is in full growth.

Knotweed growth will increase rapidly from June when the plant is most visible above ground level.

As the season progresses, this invasive weed will begin to grow even more rapidly, making it harder to get rid of.

How to identify Japanese knotweed

During spring, reddish-purple shoots will begin to emerge from the ground, but there is often much more significant growth lurking around by the time summer arrives.

Asparagus-like spears will grow rapidly from the crown-shaped buds, forming dense, bamboo stems in just a matter of weeks.

Look for tall knotweed stems

By early summer the mature Japanese knotweed stems are hollow with purple speckles and can reach up to three metres in height.

At this time, the red shoots will have turned into a distinctive green colour.

According to the Environmental and Ecological Consultancy firm, Phlorum, leaves should alternate along each side of the stem, producing an obvious knotweed zigzag pattern.

Vibrant green leaves

Japanese knotweed is known for its iconic foliage, and the bright green leaves are hard to miss in the heat of summer.

The signature heart-shaped leaves are the best way to identify this invasive plant but don’t expect to see these all year round.

If you’re dealing with knotweed, the pointed leaves will grow up to 14cm long in a short period of time, in staggered intervals on the stems.

In most cases, the foliage will disappear as the cold weather sets in again.

Delicate white flowers

Towards the end of summer, Japanese knotweed flowers provide another means to easily identify an infestation in your garden.

Look for elongated clusters of creamy white blossoms growing alongside the striking green leaves.

Unsurprisingly, this is when most people spot this invasive weed on their property, though this often means that it has been growing for some time already.

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Can you get rid of Japanese knotweed in summer?

While summer is the best time to identify a Japanese knotweed infestation, is it really the best time to start getting rid of it?

According to the experts at Phlorum, the answer is yes – you should start treatment immediately.

Phlorum said: “Summer is also an ideal time of year to start a treatment plan.

“Leaves are constantly absorbing nutrients for storage throughout the winter, so when glyphosate is painted onto leaves, the herbicide is quickly absorbed down into the plant’s rhizomes for maximum effectiveness.”

A glyphosate weed killer is generally the best remedy for invasive knotweed, but it is likely to take a few applications to be successful.

In fact, it can often take as long as four seasons to completely eradicate the plant.

Gardeners’ World recommended applying the solution to cut canes, so that the weed killer can thoroughly penetrate the plant.

Glyphosate-treated knotweed will often regrow the following spring, albeit much less vigorously, so it is important to administer a second application once this appears.

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