Japanese Knotweed Identification

The video below is a short slideshow of surveys we have carried out showing Japanese knotweed identification

Leaves

The leaves are green, shield or heart-shaped, with a flat base and are up to 12cm long.

• Shield shaped
• Flat base
• Lush green colour in summer
• Form zig-zag shaped stems

Japanese Knotweed Leaves

Main Stems

The stems are green with red or purple specks, hollow and similar to bamboo, and can grow up to 2- 3m tall, forming dense cane-like clumps.

• Purple speckles in Spring/Summer
• Regular nodes (like bamboo)

Japanese Knotweed Stems

Roots (Rhizome)

The roots consist of rhizomes, which are yellow / orange when cut, but can spread to a depth of 3m and radius of 7m.

Japanese Knotweed Roots

Flowers

Clusters of creamy flowers appear on the tips of most stems from August to October but produce sterile seeds.

• Late summer / autumn
• Spike length can be 10cm

Japanese Knotweed Flowers

What to look for in Spring

In the spring, Japanese Knotweed emerges from winter dormancy with new leaves initially being reddish in appearance with an arrow shaped tip up to 4cm long.

How to identify in Spring

What to look for in Summer

2-3 metre stems, which are hollow with nodes that resemble bamboo. The leaves will be green in colour appearing from zig-zag plant growth. In late summer the plant will start to produce white flowers.

How to identify in Summer

What to look for in Autumn

Similar to late summer, approaching late autumn the leaves start to go yellow and start wilting, this is a sign of the plant starting to pull all the nutrients from above ground.

How to identify in Autumn

What to look for in Winter

Japanese Knotweed canes will begin to die back and the plant will lose its leaves, leaving dried brittle canes. 

How to identify in Winter

Identification Service

Think you have Knotweed? Read our do’s and don’ts
Learn about PCA Certification
Book a survey

Understanding Japanese Knotweed

Japanese Knotweed is one of the most invasive plant species in the UK. It can grow up to 10cm per day, for this reason accurate identification is critical. The Rhizome (root system) below ground is the biggest problem. The plant is capable of undermining drains and other under ground services and finds weaknesses in concrete / foundations allowing the plant to cause damage.

The most cost effective way of control or removal of the plant is chemical spraying.

Find out more about treatment processes and options.

In the UK there are two main pieces of legislation that cover Japanese Knotweed.
Wildlife and Countryside Act 1981
“It is an offence to plant or otherwise cause the species to grow in the wild”

Environmental Protection Act 1990
“Japanese Knotweed is classed as ‘controlled waste’ and as such must be disposed of safely at a licensed landfill site according to the Environmental Protection Act (Duty of Care) Regulations 1991”

All of our technicians our qualified to NPTC PA1 / PA6/ PA6AW and are CSJK qualified (Certified Surveyor in Japanese knotweed)  with over 7 years of Japanese Knotweed company knowledge.

If you think you have Japanese Knotweed, please call Southwest Knotweed and we would be more than happy to conduct a survey and establish the best cause of action. We cover all parts of Cornwall, Devon and Somerset.

Japanese Knotweed Background

The most common species of Japanese Knotweed is Fallopia Japonica and is native to Japan. Introduced to the UK in the 19th century as an ornamental plant, it is now common and widely spread across the UK from Penzance to Inverness.

In the UK, all Japanese Knotweed plants are female and spread not by seed but through fragments of rhizome and stem. These fragments can be dispersed by watercourses, animals, or human activity.

This has negative impacts in the UK such as out-competing our native British plants and also adding to river bank erosion, which in turn will increase the risk of flooding.

Japanese Knotweed also has an economical negative impact, causing significant delays in construction as well as the potential of structural damage including drains and under ground utilities, not to mention the plants capability of growing through weaknesses of hard surfaces and asphalt.

Japanese Knotweed is listed under Schedule 9 of the Wildlife and Countryside Act 1981 with respect to England, Wales and Scotland. As such it is an offence to plant or otherwise cause Japanese knotweed to grow in the wild. Under the Environmental Protection Act 1990. Japanese Knotweed is classified as controlled waste.