Japanese knotweed characteristics are many, as is its being one of the most invasive plants in the UK.  Here we try and explain in a bit more detail some of those characteristics. Whilst many plants strike a resemblance with this weed making it harder for it to be identified easily.

This article has everything that you need to know about the invasive Japanese knotweed. Read on….

Japanese knotweed characteristics discussed here before treatment begins

What is Japanese knotweed?

Japanese knotweed is an aggressive and extremely invasive herbaceous plant originating from Asia. The knotweed is easily mistaken for other similar invasive plants. The plant has grown widely in the British countrywide since its arrival in the late 19th century.

The Japanese knotweed is UK’s most destructive and invasive plant. It can ravage through tarmacked lawns and properties. It can creep under structures and get to the floorboards due to its extensive root system. Its removal is challenging and quite costly, as you will learn in this article.

Main Japanese knotweed characteristics of the plant include its shovel-shaped leaves, zig-zag stem and creamy white flowers
Main Japanese knotweed characteristics of the plant include its shovel-shaped leaves, zig-zag stem and creamy white flowers

How to identify the Japanese knotweed characteristics

Timely identification of this weed is crucial to prevent damage to structures in the infested areas. Here are the characteristics of the plant:

 Unique leaves

 It is easy to recognize the weed by its heart-shaped leaves. They are pointed at the tip and form a zigzag pattern as they emerge from the stem. They are dark green, growing up to 200mm in length.

Japanese knotweed with its shovel-shaped leaves
Japanese knotweed with its shovel-shaped leaves

Tall stems

This plant can grow fast within a short period. It grows up to3 meters. The stems feature nodes and purple speckles, they are hollow and not woody like those of Bamboo. The stems will quickly change into dark brown and brittle during winter.

Tall stems of Japanese knotweed is just one of its characteristics. Growing up to 3m in height
Tall stems of Japanese knotweed are just one of its characteristics. Growing up to 3m in height

Creamy-white flowers

The Japanese knotweed has creamy-white flowers that appear towards the last weeks of summer. They occur in clusters that are about 0.5 cm wide and 10 cm long when mature. The leaves, together with the flourishing flowers, create dense foliage.

The Japanese knotweed flowers in late summer and its panicles cover the ground extensively
The Japanese knotweed flowers in late summer and its panicles cover the ground extensively

 Extensive root system

The rhizomes are the underground stems of the weed.  This root-like stem is dark brown on the outside and orange on the inside when snapped.

The rhizomes have the potential to grow up to 2 meters deep and 7 meters horizontally.

Japanese knotweed roots grow extensively underground as rhizomes
Japanese knotweed roots grow extensively underground as rhizomes


This weed can grow in any climatic condition. However, it grows faster under the sun. It can be found in riverbanks, roadsides, streams, wetlands, and wet edges around properties.

Japanese knotweed grows rapid;y by taking as much light from the sun as opposed to other plant species which do not get a look in
Japanese knotweed grows rapid;y by taking as much light from the sun as opposed to other plant species which do not get a look in

Identifying the Japanese knotweed characteristics throughout the year

We have already discussed how the plant appears. Let’s  learn how the plant evolves all year round:

Fast growth in spring

The fastest growth of this weed can be seen during spring. Its red or purple shoots emerge and are similar to asparagus. The plant grows up to 3 meters towards the end of spring.

Japanese Knotweed new shoots growing in spring
Japanese Knotweed new shoots growing in spring

Major changes in summer

The leaves are green and shovel-shaped during summer. You will notice small clusters of flowers towards the end of summer in early autumn. The stems are hollow and brown in appearance.

Japanese knotweed in summer
Japanese knotweed in summer

Stems changes in autumn

The leaves become browner and dense in early autumn. The stems will still be hollow but dark brown in appearance.

Stem and leaves change in winter

The knotweed canes die off and become dormant at the beginning of winter. The leaves change from yellow to brown and fall off. The plant falls and decomposes towards the end of winter.

How does it spread?

The knotweed spreads by vegetative means. The root system can grow from existing rhizomes or crowns. Any tiny root or stem fragments being transported from contaminated soil will grow in a new area. You must dispose of the contaminated soil carefully to avoid regrowth.

Eliminating knotweed yourself

You can dig out the knotweed yourself, but it is risky in several ways.  The plant’s extensive root system is difficult to get rid of and there is always a possibility of regrowth. Here are some tips for getting rid of the weed:

Try to get rid of the problem: You should dig up the root as much as possible to destroy regrowth. It will take months to years to completely get rid of the plant by digging up.

Do not try to get rid of the weed if you plan on selling your property: The best option is to hire a weed expert to initiate treatments on your property. Mortgage lenders will need professional reassurance when you have Japanese knotweed.

Stop the weed spread to the neighbouring land: Japanese knotweed is a problem for everyone. It spreads quickly and may lead to disputes with your neighbour if it spreads to your neighbour’s property.

Have a d discussion with your neighbour about the Japanese infestation on your property and the treatment plans in place. You may need a barrier to prevent encroachment into their property as you try to get rid of this weed.

Avoid spreading contaminated soil: The weed grows from the small fragments in contaminated soil. To avoid contamination, you should dispose of the waste at licensed landfill sites. You should also avoid handling the weed waster with your usual household waste.

It is possible to slow down the growth of the knotweed: You may use chemical methods such as weed suppressant fabrics. The landscaping fabrics are laid over the cleared soil, and this will quickly stop the regrowth of old weeds and prevent new ones from emerging.

Try Glyphosate herbicides: Glyphosate-based herbicides are the most effective chemicals for treating Japanese knotweed. Before its use, you need to cut the old stems to have optimum access to the plant. Spray the weed during summer during flowering and autumn before it dies.

Treat repeatedly until you get rid of the weed completely. It will take about six seasons or at least two years to eradicate the knotweed using this herbicide.

An area being treated for Japanese knotweed which is to be isolated
An area being treated for Japanese knotweed which is to be isolated

Seeking professional advice

If the knotweed is too stubborn to get rid of, it is advised to seek help from an expert. Seeking professional advice is pricey, but then it can be the only option you have.

Specialists have access to better weed killers and skills on how to speed up the eradication process.

Bestseller No. 1
Bayer Garden 2 x Path, Patio & Drive Weed Killer & Watering Can Set - 3 x 8g Sachets per pack treats upto 75sqm - Kills Ground Elder, Nettles, Docks, Couch Grass & Japanese Knotweed.
  • This exclusive twin pack and 9L Watering Set is everything you need for clearing weeds from paths, patios and rives including areas of tarmac, concrete and block paving.
  • Kills tough weeds and their roots including: Ground Elder, Nettles, Docks, Couch Grass, Japanese Knotweed, Brambles, Bracken & Ivy.
  • Each box contains 3 x 8g Simple ready measured soluble doses and treats up to 75sqm. Apply at any time when weeds are showing green leaf and are actively growing.
  • Sold with our durable 9L or 2 gallon capacity galvanised steel watering can with removable brass rose. Colour cannot be guaranteed. Watering can will be randomly picked and despatched.
  • Keep children and pets away from treated areas until the spray has dried.
Bestseller No. 2
Roundup Tree Stump Weedkiller, Super Concentrate 250 ml
  • Kills ivy japanese knotweed, saplings, brambles and nettles to the root
  • Kills up to 16 tree stumps
  • Contains a reusable pipette for specialist treatment of japanese knotweed
  • Kills the roots so weeds don't come back
  • Degraded in the soil by micro organisms
SaleBestseller No. 3
Weedol 011005 Pathclear Weedkiller Liquid Concentrate, 6 + 2 Tubes
  • Unique dual action fomulation, kills weeds to the root and prevents new weeds growing for up to 3 months
  • Ideal for paths, drives and patios
  • No measuring or mess - just add water
  • Creates an invisible barrier that prevents new weeds for up to 3 months
  • Children and pets need not be excluded from treated areas (once dry)
Bestseller No. 4
RootBlast - RootBlast 360 Glyphosate Home Garden Weedkiller - 1L Bottle with Integral Measuring Device Pair - Includes Pair Of gloves - 1L Makes Up to 50L
  • WEED KILLER CONCENTRATE: Rootblast's strong weed killer is both super-concentrated and tough on most broad leaf and grass weeds. It's specifically designed to bring you the best results by using systematic herbicide technology. It targets weeds from the inside and kills them at their underlying roots, preventing any future growth
  • GLYPHOSATE WEED KILLER: For optimal weed control, Rootblast have created a concentrate weed killer that contains 360g/l of glyphosate. Glyphosate is a broad-spectrum systemic herbicide and crop desiccant that is used by famers. It kills and destroys the weed without affecting the crop. By using glyphosate, Rootblast's weed killer is stronger and more effective than most other weed killers on the market
  • GLYPHOSATE HERBICIDE: This powerful and effective weed killer is designed to target weeds such as dandelion, grasses, docks, nettles, willowherb, bindweed, woody brambles, tree stumps, ivy and more. After applying Rootblast's heavy duty weed killer, the first signs of weed control are visible when the weed leaves yellow - this can take anywhere from a few days to up to 2-4 weeks. From this 1 litre bottle of glyphosate herbicide concentrate, you can make up 50 litres of product when it's diluted
  • DOCK, GRASS & DANDELION KILLER: Alongside this industrial strength weed killer, you'll receive a pair of protective gloves as well as the integral measuring device attached to the bottle. The gloves provide you with protection to ensure your experience is as easy and safe as possible. The integral measuring device is an inbuilt measuring cup, simply remove cap and carefully squeeze the container until the cup is full
  • TOTAL PROTECT WEED GARDEN SPRAY: This easy to use product is available as a ready to use tough, concentrated weed killer that comes with a integral measuring device attached and protective gloves. Use by professional garden and farmers, this product can tackle your weed problem and kill the weed from the root - the ultimate weed killer!
Bestseller No. 5
Rootblast Glyphosate Weedkiller 4 x 100ml Concentrate with 5L Pump Sprayer
  • For use on unwanted vegetation and areas not intended to bear vegetation
  • Contains 72 g/l glyphosate for effective control of annual and deep-rooted perennial garden weeds, including grasses*, docks, nettles, willowherb, dandelion and bindweed. Also suitable for woody brambles, tree stumps and Ivy.
  • Coverage up to 66sqm per sachet

Want to know more about Japanese Knotweed characteristics?

Knotweed Removal aims to provide the most up-to-date information, help and advice for YOU to make informed decisions. If you are unsure or uncertain about how to proceed, please reach out to us and we will gladly come back and advise you as best we can.

Governmental advice can be found here and the UK law covering the removal of Japanese Knotweed as stated under the Wildlife and Countryside Act 1981 can be found here.

The best means to contact us is via our email – hello@knotweedremoval.tips

Do not forget we have a library of blogs covering many areas relevant to Japanese Knotweed, our free downloadable How-to Guides and Product Reviews on the latest methods being employed to eradicate or remove Japanese Knotweed.

Knotweed Removal, UK

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