Key signs of ‘troublesome’ Japanese knotweed to look for in autumn

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Japanese knotweed grows vigorously between spring and autumn before dying down to the ground in winter. This problematic weed is much harder to spot as it enters its dormant period, but there are a few crucial signs to look out for right now, according to experts. The team at Japanese Knotweed Specialists noted the importance of “keeping an eye out” for invasive growth on your property in autumn to identify it “early on” and be in with the best chance of tackling it effectively.

What does Japanese knotweed look like in autumn?

In its peak season, Japanese knotweed can grow 20cm per day, up to 2.5 metres tall. This nuisance weed can infiltrate both concrete and bricks, posing a significant threat to the stability of property.

While it is much less vigorous in the period between summer and winter, there aren’t many changes in the way it looks.

There is only one noticeable difference in its appearance at this time of year, according to the team at Japanese Knotweed Specialists.

Speaking exclusively to, they said: “As summer turns to autumn, Japanese knotweed changes only slightly as the flowers are in full bloom until October.

“When the plant begins to wilt, the leaves turn yellow and the stems become dark brown and dormant.”

Until this happens, the best way to identify it is to look for the heart-shaped leaves, creamy white flowers and zig-zagging growth patterns.

According to JKS, the widespread growth continues to fade from green to brown until winter, when the leaves fall off completely.

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As the most invasive plant found in the UK, Japanese knotweed requires specialist treatment to remove and could land you a large fine of up to £5,000 if you fail to get this done.

Section 14 of the Wildlife & Countryside Act 1981 states: “If any person plants or otherwise causes to grow in the wild any plant which is included in part Two of schedule Nine, he shall be guilty of offence.”

This means that if you let Japanese knotweed spread to private land, such as your neighbour’s garden, you could be responsible for the compensation and any legal fees incurred in addition to the removal costs.

For this reason, it is crucial to keep an eye out for the first signs of an infestation at all times of the year.

The team at JKS added: “Identifying Japanese knotweed early on is essential in tackling it effectively and will also save you money not having to fight a major infestation.”

When it comes to removing weeds from your property, attempts at doing it yourself should be avoided at all costs.

The specialists explained that amateur removal will only “make matters worse” due to the vigorous nature of the plant.

They said: “Even the smallest remnant of Japanese knotweed can be the start of a whole new plant, as rhizomes left over in the soil can reproduce and create a new infestation.”

Its ability to grow in almost any climate is what makes this weed so “troublesome” for homeowners, renters and gardeners alike.

According to Japanese Knotweed Specialists, the plant can continue to grow during its dormant phase too.

They said, “even in winter, when the knotweed remains dormant above ground, below ground the roots are still present and may continue to grow.”

On the soil surface, the plant will die off until the following spring when new shoots appear.

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