Japanese Knotweed, an invasive plant species originating from East Asia, may appear innocuous at first glance, but it can wreak havoc on your garden, your home, neighbouring properties and it can seriously affect the value of your property and even land you a whopping great fine, if you knowingly allow it to spread. So if you’re planning on selling up or you’re looking for a new home then it is vital that you know what it is and how to get rid of it and how to spot potential signs of it at any property that you are considering buying. This week’s blog covers how to identify it, what to do if you find it in your garden, its impact on property values, and the top ten Japanese Knotweed hotspots in the UK, with an interactive heatmap showing you exactly where to find it!

Identifying Japanese Knotweed

Before you can tackle the issue of Japanese Knotweed, you must first be able to identify it correctly. This resilient plant typically features the following characteristics:

  • Red or Purple Stems: In spring and early summer, Japanese Knotweed’s young stems are red or purple, gradually turning green and hollow as they mature.
  • Distinctive Leaves: Its leaves are shield-shaped, with a flat base and a pointed tip. They are arranged alternately along the stem and have a distinctive zigzag pattern.
  • Clusters of Small White Flowers: Japanese Knotweed produces clusters of small, creamy-white flowers in late summer.
  • Growth Pattern: It can grow up to 3 metres in height and spreads rapidly, often forming dense thickets.

Plants which are commonly mistaken for Japanese Knotweed

The following species of plant are commonly mistaken for Japanese Knotweed, so don’t be too concerned if you find any of these in tour garden, although Himalayan Balsam is classed as an invasive species it is not classed as critical and you won’t get fined for having it on your property.

  • Himalayan Balsam: Known for its pink, trumpet-shaped flowers.
  • Bamboo: Although unrelated, bamboo has a similar appearance to Japanese Knotweed
  • Bindweed: Recognisable by its twining, climbing habit, smaller leaves and ‘parachute’ flowers
  • Broad-leaved Dock Often found growing on wasteland and used for curing stinging nettle stings
  • Himalayan Knotweed This looks very much like Japanese knotweed and is also an invasive species, but not on the same scale
  • Himalayan Honeysuckle This is not an invasive species and can be found growing in many gardens across the UK. Recognisable by it’s pretty cascading maroon flowers and berries which are very popular with bees and other wildlife
  • Russian Vine A pretty climbing plant that can grow very rapidly, with pinky-white blooms
  • Houttuynia This can be mistaken for Japanese Knotweed due to it’s red stems but it has variegated leaves and only grows at ground level

Invasive plant specialists, Environet have created this useful Japanese knotweed heatmap to help you discover exactly how many known cases of Japanese knotweed there are near you – or on or near any property that you are hoping to buy.

Knotweed is easier to identify in the summer, but during the autumn and winter it dies back and can be harder to spot – and therefore easier to conceal so it is a good idea to check out the heatmap to see if anything has been reported in the area if you are a looking at buying a home.

What to Do If You Find Japanese Knotweed in Your Garden

Discovering Japanese Knotweed in your garden can be unsettling, but it’s essential to act swiftly and responsibly to prevent its further spread:

  • Don’t Panic: While Japanese Knotweed is invasive, it can be managed with the right approach.
  • Avoid Disturbing It: Refrain from cutting or digging up the plant, as this can exacerbate the problem. It can grow from just a tiny fragment of root in the soil, so you are much better off calling in the experts to help.
  • Seek Expert Advice: Contact a professional invasive species specialist or your local authority to confirm the presence of Japanese Knotweed and develop a plan for its removal.
  • Document and Report: Take photographs and keep records of the infestation for future reference, as it may be necessary for legal purposes.

Gov.uk have lots of useful information on their website to help you to stop Japanese Knotweed from spreading including how to treat it and dispose of it safely. You can also contact the Environment Agency for help if you:

  • Have more questions about how to handle waste containing Japanese Knotweed
  • Want to find out more about when you need a licence to dispose of Japanese Knotweed
  • Want to complain about waste producers who are not telling people they employ how to transfer Japanese knotweed – this is breaking the rules on their waste duty of care

Email enquiries@environment-agency.gov.uk or telephone 03708 506 506

Impact on Property Value

Knotweed is not just a nuisance in your garden; it can significantly affect the value of your property:

  • Mortgage Issues: Many mortgage lenders are cautious when dealing with properties affected by Japanese Knotweed as it can cause structural damage, which can lead to difficulties securing a mortgage.
  • Liability: Failing to address Japanese Knotweed can result in legal liability if it spreads to neighbouring properties.
  • Decreased Property Value: Infestations can reduce your property’s market value by thousands of pounds. According to Yopa “knotweed can reduce a property’s value by between 5-15%, and depending on the size of the infestation and its proximity to surrounding buildings, it could even make a property unsellable”

Top Ten Japanese Knotweed Hotspots in the UK

Whilst Knotweed can be found throughout the UK, certain regions are more prone to infestations. Here are the top ten hotspots this year:

  1. Swansea, with 1,350 known cases in 2023
  2. Bolton, Machester, with 1,010 cases
  3. Bristol, with 986 cases
  4. Cardiff, with 872 cases
  5. Preston, Lancashire, with 857 cases
  6. Nottingham, with 803 cases
  7. Derby, with 711 cases
  8. Caernarfon, Gwynedd, with 708 cases
  9. Llanelli, Carmarthenshire, with 706 cases
  10. Bridgend, with 664 cases.

Japanese Knotweed is a formidable adversary for homeowners and potential buyers. Identifying it correctly and seeking professional assistance is crucial to prevent its spread and protect your property value. If you suspect that it may be growing in your garden, take prompt action and get professional help in order to mitigate its impact and preserve the beauty and structural integrity of your home.

Picture Credit: Abraham on Wikimedia Commons