How To Identify Japanese Knotweed [Free Tools, 100% Accurate]

Japanese Knotweed is an invasive plant species that first reached the UK in 1850. The UK’s Environment Agency has since labelled it as “indisputably the UK’s most aggressive, destructive, and invasive plant”.

Japanese Knotweed can grow through brick and building foundations. This has two consequences:

If it’s within your boundary your property will become unmortgageable and difficult to sell until treated.
It can cause serious damage to your property, including structural issues.

If you’re concerned that you may have Japanese Knotweed on your property then the first step is identifying it.

What does Japanese Knotweed look like?

Its leaves are heart or shovel-shaped, and up to 14cm (5.5in) in length. They’re formed in a zig-zag pattern along the stems. The stems grow from bamboo-like canes which grow up to 2.1m (7ft) tall. In late summer/early autumn it produces creamy-white flower tassels, which grow up to 15cm (6in) in length.

Japanese Knotweed looks different depending on the time of year though, which makes things slightly more complicated.

You don’t need to be an expert to identify Japanese Knotweed though. There are free tools and services (including ours) which will assist with Japanese Knotweed identification.

Let's get into some of the details about what it looks like, and then cover the tools and services available.

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1. Japanese Knotweed Identification (throughout the year)

So, how do you know if you have Japanese Knotweed?

The plant has some quite distinctive characteristics, but it looks different throughout the year. This can make identification a little more difficult.

There are some wonderful guides online with dozens of pictures and detailed descriptions. They document everything about Japanese Knotweed in each of its seasons covering everything from leaves to stems, buds and rhizomes.

But if you're reading this we're going to assume you're not an expert gardener... You just want to know if you have Japanese Knotweed!

We're going to summarise some of the key features then skip forward to tools and services. (You can use these free tools and services to get a Japanese Knotweed identification in the next 24 hours).

1.1. Leaves

Mature leaves are quite distinctive. They're light green in colour, and heart or shovel-shaped. They grow up to 14cm in length.

Younger leaves are smaller and may still be partially "rolled up". Their most distinctive feature at this stage are their dark red veins.

New leaves are dark red in colour, and usually 1-4cm in length.

A picture of mature Japanese Knotweed leaves. Source: Koppert.com — A collection of mature leaves.
Source: Koppert.com a biologicial research and development company working on solutions for Japanese Knotweed eradication.

1.2. Stems

Leaves grow on alternate sides along the stem. This creates a distinctive zig-zag formation towards the end of them.

Leaves grow on alternating sides of the stem, creating a distinctive "zig-zag" pattern
Source: Phlorum.com, an environmental consultancy specialising in Japanese Knotweed

1.3 Shoots

Stems are "bamboo-like". They're green in colour but feature reddish-purple specks. They grow quickly, and can grow to around 2.1m (7ft) in height. They're hollow rather than woody, and also grow in a slightly zig-zag pattern between the nodes.

Source: Knotweedhelp.com, a UK company offering guidance on how to deal with Knotweed infestations.

2. Things that look like Knotweed (but aren't)

On their advice page about Knotweed the Royal Horticultural Society identify several types of plants that are often confused with Japanese Knotweed.

They include:

Fallopia baldschuanica (Russian vine)
Leycesteria formosa (Himalayan honeysuckle)
Houttuynia cordata
Persicaria microcephala ('Red Dragon')

Other similar-looking plants include Bindweed, Bamboo, Horsetail, Buckwheat, Lesser Knotweed, and Himalayan Balsam.

We could write for hours about the differences between those species and Japanese Knotweed, but let's get to the nuts and bolts of it: Tools and services to get an identification of Japanese Knotweed today.

3. Free Japanese Knotweed Identification Tools & Services

As we've covered, Japanese Knotweed is a serious problem for homeowners and their properties. If you have knotweed you should act quickly, and the first step is identifying it. But no one wants to obtain a biology degree to check if they have Japanese Knotweed.

There are two far better ways to find out. Take advantage of free tools and services. We've got two to suggest for you.

3.1. Our Japanese Knotweed Identification service

We offer a free Japanese Knotweed identification service in association with KnotweedHelp.com. Knotweed Help is a consumer advice website started by Cobleys Solicitors, who are authorised and regulated by the Solicitors regulation Authority (SRA no. 633045).

If you suspect you may have a Japanese Knotweed infestation around your property, contact us for a free, no-obligation advice. We can help confirm identification of the plant within 24 hours, and help you navigate your options.

Get an Identification within 24 hours

To get a FREE identification within 24 hours either:

Email your photos to advice@homesellingexpert.co.uk. Include your property address, contact telephone number, and a short history of the issue. (For example when you first noticed it, if it's within your boundary or a neighbour's boundary, etc)
OR send the same information to us via Whatsapp, on 07894 458090.

We'll contact you with an identification of the plant, and free, no-obligation advice to help explore your options.

3.2. "PictureThis" smartphone app

An alternative is the incredible PictureThis smartphone app. PictureThis is an online plant encyclopaedia and identifier. Use your smartphone camera to take and then upload pictures of the suspected Japanese Knotweed.

The app then uses sophisticated AI to analyse the image and come back with an identification. It can identify over 10,000 plants - including Japanese Knotweed - in seconds. It's truly an incredible piece of software.

Step 1. Download the app

The app is free to download here from the App Store (for Apple devices) or Google Play (for Android devices).

Screenshot of PictureThis app listed in the app store. — Find PictureThis in your smart device's app store

Step 2. Start a free trial

Although PictureThis charges an annual subscription of £24.99 it offers a free 7-day trial. As long as you cancel within the first 7 days you won't pay a penny. This is more than long enough to get your free Japanese Knotweed identification!

Step 3. Take a picture in the app!

It's really as simple as this. Hit the "camera" button in the middle of the menu, and take a picture of the suspected knotweed. Within seconds the app will come back with an identification. It may be worth doing this a few times using pictures of different parts of the plant to be certain.

GIF of using the PictureThis app to complete an identification of Japanese Knotweed.. — PictureThis uses AI to analyse your photos, and returns an identification within seconds.

4. I've confirmed my Japanese Knotweed identification... What next?

If you've followed the steps in this article, you may now have a confirmed case of Japanese Knotweed.

Because Japanese Knotweed is an invasive species you actually have legal obligations surrounding it. It might be a good idea to familiarise yourself with the guidelines the Environment Agency have set out. For example:

"You do not have to remove Japanese knotweed from your land, but you could be prosecuted or given a community protection notice for causing a nuisance if you allow it to spread onto anyone else’s property."
- Gov.UK guidance on preventing the spread of Japanese Knotweed

You've got a few options now. The best one will depend on how extensive the infestation is, whether or not you can afford a knotweed removal plan, and whether or not you're hoping to sell the property.

Here are some things to consider:

Knotweed removal: If you're looking to remove the knotweed, email advice@homesellingexpert.co.uk, asking for a Knotweed Removal specialist.
Knotweed compensation: You may be able to find a solicitor who can help seek compensation for you.
Selling a house with Japanese Knotweed: If you're looking to sell a house with Japanese Knotweed we can help determine the best route of sale. Take this free quiz we've designed for you: