What Is Japanese Knotweed? Identification and What to Do if You Find One in Your Garden?

Last update: 1 month ago

Japanese knotweed is one of the most invasive perennials, known for its ability to cause severe damage to properties, no matter if residential or commercial. Sometimes, Japanese knotweed identification can be difficult since there are four more species of it and other Japanese knotweed look-alikes. In this article, we’ll cover how to identify Japanese knotweed, plants mistaken for Japanese knotweed and what to do if you find one in your garden.

What does Japanese knotweed look like?

Japanese knotweed produces a lot of foliage and vigorously growing stems, which makes the perennial easy to identify but only in the growing season. Below, we’ve listed detailed characteristics of the plant. 

  • Japanese knotweed flower – You’ll recognise the plant by its small creamy-white clusters of flowers reaching 10cm. The blossoms appear in late summer and early Autumn. If you notice blooming Japanese knotweed, that means that the plant is well established, therefore its removal will be challenging.
  • Japanese knotweed leaves – In most cases, knotweed identification starts with the leaves. They’re heart- and shovel-shaped with a lush and bright green appearance. Each leaf has a tapered end and is arranged in a zig-zag growth pattern along the stem. However, the identification of Japanese knotweed leaves will be impossible in winter as the plant’s foliage wilts during the cold months.
  • Japanese knotweed stem – If you’re wondering how to recognise Japanese knotweed, especially if there are no leaves, look at the stems. In spring, when first emerging, the Japanese knotweed stems will be red or reddish-brown in colour. They look very similar to bamboo stems with a hollow inside and easily snappable. But note that this colouration won’t last throughout the year. With the coming of winter, the Japanese knotweed stems will turn brown and become brittle. Unfortunately, during the cold months, all that’s left of the previously lush plant are broken and bamboo-like stems, which makes the winter Japanese knotweed identification nearly impossible.
  • Japanese knotweed roots – The roots of that invasive plant are the biggest problem, as they can reach up to 3 metres in depth and 7 metres horizontally. Even the smallest viable rhizome can give a new life to the plant and be the culprit behind it spreading uncontrollably. Japanese knotweed roots can reach up to 20cm in diameter, making the plant hard to dig. That’s why in most cases, the plant’s removal involves digging it out with the help of machinery, combined with the use of chemical control. The most disconcerting fact about Japanese knotweed is that it can spread underground unnoticed during the winter. Even the most observant person will not be able to notice its presence until the spring when they can see the first sign of new shoots beginning to develop.

 Plants mistaken for japanese knotweed

There are numerous plants that look like Japanese knotweed, and many homeowners get suspicious when they notice a sudden appearance of an unknown shrub-like plant in their garden. Hence, it’s important for you to get familiar with Japanese knotweed look-alikes and rule out every possibility before panicking. For example, bindweed also has heart-shaped leaves and looks almost the same way as Japanese knotweed except that it is a climbing plant and will wrap around your trees and walls. Another good example of a plant that looks like Japanese knotweed is the broadleaf dock. The difference here is in the stems, as the broadleaf dock’s stems are shorter. 

Below you can find more plants commonly mistaken for Japanese knotweed:

  • Buckwheat;
  • Lesser knotweed;
  • Horsetail;
  • Giant knotweed;
  • Himalayan honeysuckle;
  • Dwarf knotweed;
  • Bamboo;
  • Russian vine;
  • Dogwood;
  • Himalayan balsam.

What does Japanese knotweed do?

Since it’s not poisonous or something, Japanese knotweed does not pose a threat to people or animals, it cannot physically harm you. However, Japanese knotweed dangers are more financial and concern many homeowners, property sellers and potential property buyers. 

If it happens that homeowners discover Japanese knotweed in their garden, they’ll have to face the fact that their home’s value will depreciate significantly. And when it comes to potential property buyers, they may decide to spend a lot of money on a survey, in order to find out if there is a Japanese knotweed infestation. Unfortunately, if they discover such problem, there is no legal recourse for them, and no one will recover all the money spent on the survey. 

You might be wondering why is all that? What does Japanese knotweed do so much? Well, you may be shocked to learn that Japanese knotweed can and will displace building foundations, patios, deckings, flood defences, garden sheds, greenhouses, fences and everything that got in its way if not removed in a timely manner. 

In extreme infestation cases, Japanese knotweed can even break into houses since it can grow through concrete. That happens rarely and is usually a result of a very severe infestation and weak building construction, but you should still be concerned if you find Japanese knotweed in your garden. That’s because even if it doesn’t break through your floor, there is a significant risk that the plant may damage or destroy some of the brickwork or your patio. 

History knows cases in which homeowners have been advised to demolish their entire homes since the foundations got severely damaged and the plant already found its way through floorboards and skirting boards. 

What to do if you find Japanese knotweed?

Actually, it’s more about what not to do than what to do if you find Japanese knotweed in your garden. For instance, don’t be tempted to cut, pull or trim the weed since that will lead to it spreading uncontrollably. That also applies to the area around the weed. In addition, it might not be illegal to have Japanese knotweed in your garden, but it is absolutely illegal to throw Japanese knotweed cuttings or stems in your general green waste bin. 

Never try to kill Japanese knotweed with some domestic weed killers – that won’t help. On the contrary, it will make the Japanese knotweed removal process more complicated. That’s because when treated professionally, the plant should be in the best of health and condition. 

Don’t hide the infestation from your neighbours, either, since this may land you a fine. Yes, it is your responsibility to notify all of your neighbours as there is a big chance that their gardens will also need an inspection. Remember that Japanese knotweed is a community problem, and you’ll be glad to know if there is Japanese knotweed in the neighbours’ garden.

Now, let’s talk about what to do about Japanese knotweed. After you’ve informed your neighbours, the second thing you have to do is to call professional Japanese knotweed control and removal experts

They’ll make sure to permanently eradicate the invasive plant from your property by getting rid of even the smallest rhizome. The professionals will arrange an on-site survey and identify how severe the infestation is. Then, you’ll be provided with an eradication plan and responsible disposal of the plant. 

Remember, you’re not allowed to bury, burn or throw away Japanese knotweed without the permission of your local council and the Environment Agency.

What to do if your neighbour has Japanese knotweed?

Noticing Japanese knotweed in your neighbour’s garden can be stressful, as it won’t take long for it to appear in yours. In such a case, you have one option – to have a conversation with your neighbours, asking them to treat their land before Japanese knotweed has the time to spread to neighbouring ones. There is not much that you can do with Japanese knotweed in neighbours’ gardens since it’s not illegal to have one. However, if your neighbours don’t take action on time and the invasive plant spreads to your property, then you have the right to file a claim against them. 

On this note, a Japanese knotweed infestation within 7 metres of your property can decrease your house’s value, and once it reaches your garden, it can lead to various types of damage and costly repairs. So, what to do if neighbours have Japanese knotweed but refuse to treat it? Well, your very best option is to get a Community Protection Notice, which will force your neighbours to take action and eradicate the invasive plant. 

However, it’s good to keep in mind that in some cases, it’s hard to estimate where the infestation started. If you share a garden with your neighbours and the borders are not precisely defined, then the best course of action for all parties is to reach a mutual agreement on sharing equally all Japanese knotweed removal expenses. 

Get rid of Japanese knotweed for good! Call and book the professional gardeners!

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The Bottom Line

By itself, Japanese knotweed might not be dangerous but it requires careful planning, in terms of its proper management. Getting rid of one can be a very complicated, time-consuming and expensive job, especially if the infestation is severe. The best solution you have is to contact a professional Japanese knotweed removal company and let them guide you through the process of eliminating the problem for good.

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2 CommentsLeave a comment

  • Hello, we had a casual gardener doing some work in our garden and he says he found japanese knotwood. This sounds very worrying but I see that there are lots of other things it might be so we’re hopeful he got it wrong and we have something more innocent.
    Can we get a specialist to look at it and let us know please, and how much would that cost?

    • Hi Ross,

      You can book a free on-site survey with us and we’ll send a knotweed removal expert to inspect your property and confirm if there is a knotweed invasion. You can read more about our knotweed eradication service on this page. To find out if we cover your area, fill in your postcode details through the “Check prices & availability button” or get in touch via phone.

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