Revealed: Hertfordshire's Japanese knotweed hotspots

The fast-growing, invasive plant species, Japanese knotweed, can affect property prices

The fast-growing, invasive plant species, Japanese knotweed, can affect property prices - Credit: Getty Images/iStockphoto

The areas of Hertfordshire most seriously affected by Japanese knotweed have been revealed. 

Watford, Elstree and St Albans have all been identified as hotspots for the invasive plant, which is most prevalent during the summer months. 

Japanese knotweed expert, Environet, has created a live online tracker to help people locate and record the pest plant.

Watford is Hertfordshire's ultimate Japanese knotweed hotspot. 

Watford is Hertfordshire's ultimate knotweed hotspot. - Credit: Environet

The tracker shows that there are currently 62 occurrences of Japanese knotweed within a 4km radius of Watford's WD19 4SG postcode, 45 within the same distance of Cheshunt's EN7 6LB, 39 surrounding Elstree's WD6 3QU and 31 around St Albans'  AL2 2DD.

Other areas highlighted on the heat map include Harpenden, Welwyn Garden City and Hatfield. 

When did Japanese knotweed arrive in the UK? 


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Japanese knotweed arrived here in the 1840s, among a selection of Chinese and Japanese plant species delivered to Kew Gardens. 

Originally intended to be used as an ornamental garden plant, it quickly became recognised as a pest. 

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What does Japanese knotweed look like? 

Heart or shovel-shaped leaves are knotweed's most distinctive feature; appearing in a zig zag formation, they can grow up to 14cm long. Another indicator is the purple flecks along the canes. 

Reynoutria japonica Asian or Japanese knotweed

Getting rid of Japanese knotweed can be a difficult task. - Credit: Getty Images/iStockphoto

The earliest signs are of reddish-purple shoots appearing from pink buds at ground level. 

When are you most likely to see Japanese knotweed?

Its peak growth period is between May and July, when its bamboo-like stems can increase in height by 10cm per day, potentially reaching more than 2.1m. 

Knotweed dies back to ground level during the winter months, emerging from rhizomes underground in early summer. 

Japanese knotweed can grow taller than 2m.

Japanese knotweed can grow taller than 2m. - Credit: Getty Images/iStockphoto

How can you get rid of Japanese knotweed? 

Eradication can be challenging. While it may be possible to tackle knotweed by yourself,  it's classed as 'controlled waste' and can only be disposed of at licensed landfill sites (unless its allowed to dry before being burnt). It should never be included in normal household waste or put out as part of green waste collection schemes. Alternatively, knotweed contractors (such as Environet) can manage its removal. 



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