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Great Tips For Identifying Japanese Knotweed.

Identifying Japanese Knotweed infographic

What is Japanese Knotweed

Japanese Knotweed is a non-native specie of plant, that was brought over from Japan in the Victorian era. It grows rapidly and is notoriously painful to get rid of, specialist treatment is usually then most common way of getting rid of it, however it can be done yourself.

The plant completely dies back in the winter months and lies ‘dormant’ until the spring. As mentioned, before it grows very quickly… up to 10cm per day, so the characteristics you need to keep your eye out for change often due to it’s aggressive growth.

Red and Purple Shoots

One of the first notable signs of a Japanese Knotweed infestation are green shoots with red and purple spots, these usually crop up in spring usually April/May, however it can be earlier if the spring is warmer. The shoots look similar to asparagus and small curled up leaves will start to stick out from the shoot, these new leaves are usually a red or purple colour.

Japanese Knotweed Shoots
Fresh Japanese Knotweed shoots, deep red and purple in colour and look similar to asparagus.

Bamboo-like Stems

As the Japanese Knotweed grows the stems will continue to grow at a rapid pace, significantly outgrowing any plant around it by height. They continue to be covered in the red and purple spots, as they become more mature in the summer, they have a similar look to bamboo and when snapped in half they are hollow. In winter, these stems become dry and brittle and turn brown as they start to die off.

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Here you can see the distinct colouring of the Japanese Knotweed, as well as it’s unusual zigzag growing pattern.

Heart-shaped Leaves

Another strong characteristic to look out for is the leaf shape of Japanese Knotweed, for the most part they’re shaped like love hearts with flat edges at the top near the stem, however some like to describe this as a ‘shovel’ or ‘spade’ shape. In terms of colour they have very vibrant lime green colour. They grow up to 20cm in length! And they grow off purple and red tone stems.

Japanese Knotweed heart shaped leaf large
An example of Japanese Knotweed leaf shape.

 Rhizome Root System

The root system or ‘Rhizome’ is the reason why Japanese Knotweed is so difficult to eradicate. If you look to the bottom of where all the bamboo like shoots is coming from then you’ll be able to spot the rhizome ‘crown’ this is where all the stems grow from, and the plant gains all its nutrients from the ground. If you manage to unearth one and cut into in it will be an orange colour on the inside, however cutting into the rhizome is not advised as a tiny fragment of that rhizome can cause more Japanese Knotweed to grow.

Rhizome crown of Japanese Knotweed
Part of a Japanese Knotweed Rhizome system and the rhizome crown, you can see where the bamboo like stems start to grow from.

Zigzag Growth Pattern

The stems of Japanese knotweed grow in a noticeable pattern, the purple / red toned stems grow in a zigzag form and leaves grow from each corner of the zigzag but on alternating sides as it moves down the stem. It is a very distinctive pattern when you spot it forming.

zigzag stem of Japanese Knotweed
The zigzag formation of how the stems grow, the leaves grow on alternating sides.

Clusters of White Flowers

In the middle of summer, Japanese Knotweed starts to produce clusters of small creamy white flowers that grow on the stems between the leaves. The flowers are around 0.5cm wide. These flowers are what caused the initial attraction and the reason they were brought over to the UK.   

creamy white flowers of the japanese knotweed
The clusters of creamy white flowers, grow on the stems next to the leaves.

 In The Autumn

In the autumn time, the plant growth stops and starts to slowly die back. The stems move from a green colour with the red and purple flecks and change to a more solid red and purple colour. The creamy white flowers begin to die and fall off the stems. As well as this the leaves start to turn from the vibrant green colour to yellow, eventually dropping off the stems.

Yellowing Japanese Knotweed in autumn
The luscious green leaves, start to yellow in the autumn time and fall off the stems.

In The Winter

As winter moves in the remaining leaves continue to fall and the shoots die back. After this the Japanese knotweed remains but leave dead, hollow stalks which become a red almost brown colour, and look remarkably similar to bamboo. In the cases of a mild autumn with no frost, some stems can remain, and, in some cases, new shoots can emerge.

Dead winter Japanese Knotweed
In the winter time Japanese Knotweed is barely distinguishable other than the remaining hollow canes.

Still Unsure If You Have A Japanese Knotweed Infestation?

If you still can’t figure out if you have Japanese knotweed on or near your property, then you may want to speak to a professional to help you identify it, you can contact us today and we should be able to give you peace of mind.

Also get in touch if you’re confident that you have an infestation, we can help you to treat the problem and can try help you gain compensation if it has ended up on your property from neighbouring land.

Methods of Removal

If you’ve tried to get rid of Japanese Knotweed before then you know that just trying to keep cutting it back doesn’t work at all. So the next most obvious method would be to try and dig the root system up to, however small fragments (anything larger than 0.7g) can allow the plant too grow back, so you’d obviously have to be very delicate. If you manage to dig the lot out you still need to get rid of the waste and that isn’t just as easy as taking it to the local tip.

However, the Royal Horticultural Society (RHS) provides useful information on removing the plant on its website:

Try a glyphosate-based weed killer such as Roundup Tree Stump & Root Killer.

Once under control, the removed knotweed must be disposed of at a licensed landfill site. The Environmental Protection Act 1990 classifies it as ‘controlled waste’.

Use of herbicides such as Roundup works best against Japanese Knotweed however there is a general consensus that it should be injected into the stems rather than just being sprayed on to the plant. This is can either be done by using a syringe to inject the herbicide into the plant stem. Or by snapping some of the stems and pouring the herbicide into the hollows of the stem. In both cases it allows the herbicide to work into the plant and into the rhizome system.

It’s advised to get it sorted out by professionals as some mortgage providers will require proof that any knotweed found on a property has been treated professionally. This would also make disposing of it easier, as specialist Japanese knotweed contractors are also required to be registered waste carriers.

So in all it’s probably easiest to have a professional do the work although this does come at a price as it isn’t usually a one time treatment, in some cases repeated revisits over the course of a few years is needed depending on the severity of the infestation.

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