FREE JAPANESE KNOTWEED IDENTIFICATION SERVICE

Why is it important to identify Knotweed early?

Since Japanese knotweed (Reynoutria japonica) is such an invasive and resilient weed, it is important to be able to identify it early. Japanese knotweed can be treated with herbicide, and this will stop the aerial growth that you see above the ground, but the roots – known as rhizomes – are capable of supporting life for up to 20 years.

Japanese knotweed can re-emerge and re-grow of its own accord any time, but especially if the contaminated ground is disturbed by gardening or construction activities. If the Knotweed infestation is left unchecked for several years, it can spread and cause a range of issues including:

• Impeding amenity land use
• Increase change of land use costs
• Material damage to hard standing structures
• Devaluation of property
• Creating legal issues

In the UK, we only have the ‘female version’ of the plant. The roots of Japanese knotweed are known as rhizomes, or ‘creeping rootstalk’. These are a horizontal underground plant stems that produce the shoot and root systems of new plants. These networks can stretch for 3 metres or more from the visible ‘areal growth’ of the plant. Even small fragments of rhizome can give rise to a new plant. This is why it is so important to learn how to identify Japanese knotweed.

How to Identify Japanese Knotweed in Spring

Like many species of weed, knotweed is very active during the spring months. This is a good time to watch for signs of knotweed growth in your garden, business premises or land.

New growth appears as rapidly growing soft red/purple shoots reminiscent of asparagus spears, growing into stronger, upward shoots with hollow stems that look like bamboo and can grow up to 10cm per day. This new growth forms dense thickets, known as stands. The emerging leaves grow on alternate sides of the stem producing a zig-zag pattern in the stem, with a leaf shooting from each ‘zig’ and each ‘zag’.

Key Facts about Japanese Knotweed in Spring

• Knotweed is particularly active during spring months.
• New growth resembles asparagus spears, soft red/purple in color.
• Stems grow stronger and resemble bamboo, with growth rates up to 10cm per day.
• Emerging leaves form a zig-zag pattern on the stems.
• Dense thickets known as stands are formed from new growth.

Still unsure? Use our free identification service. Use the form at the top of this page to send us a few pictures of the plant that concerns you, or email your pictures to ident@knotweed.co.uk.

How to Identify Japanese Knotweed During Summer

During the summer months, Japanese knotweed becomes fully formed with large shovel shaped green leaves, forming a dense canopy. Leaves can grow up to 200mm long. Japanese knotweed canes grow to around 3 to 3.5m tall. It will often form as a semi-dense stand of upright stems. As summer continues, knotweed begins to form clusters of creamy-white elongated flowers. The canes grow to around 3 to 3.5m tall in summer, often forming a semi-dense stand of upright stems, with lush green foliage.

Key Facts about Japanese Knotweed in Summer

• Knotweed has large shovel shaped green leaves forming a dense canopy.
• Leaves can grow up to 200mm long during summer.
• Canes grow to 3 to 3.5m tall, forming a semi-dense stand of upright stems.
• Clusters of creamy-white elongated flowers form as summer progresses.
• Identifying knotweed can be challenging due to other flowering plants and weeds.

During the summer months, the volume of other flowering plants and weeds can make it tricky to identify knotweed. Our experts are fully trained to identify knotweed (and other invasive species).

Still unsure? Use our free identification service. Use the form at the top of this page to send us a few pictures of the plant that concerns you, or email your pictures to ident@knotweed.co.uk.

How to Identify Japanese Knotweed During Autumn

In Autumn the dense covering of leaves will remain, however, they start to turn yellow and orange and appear more brittle. The leaves wilt as we move into September and October. At this stage the knotweed plants are still about 2-3 metres tall, and the hollow stems start to turn brown. Once the leaves start to fall the canes become more easily identifiable.

Key Facts about Japanese Knotweed in Autumn

• The dense covering of leaves starts to turn yellow and orange.
• Leaves become more brittle and start to wilt in September and October.
• Knotweed plants remain tall at about 2-3 metres during this season.
• The hollow stems of the plant begin to turn brown.
• As leaves fall, the canes or stems become more distinguishable.

Still unsure? Use our free identification service. Use the form at the top of this page to send us a few pictures of the plant that concerns you, or email your pictures to ident@knotweed.co.uk.

Identifying Japanese Knotweed in Winter

Identifying Japanese knotweed in Winter can be a little tricky as some of the most identifiable signs are its leaves and flowers, and in Winter knotweed will have lost all of its leaves, but the long clustered shoots will remain. These canes will die off and turn brown and brittle however will remain erect through the winter if left undisturbed.

This isn’t the end of the weed, however – its crown and rhizome remain dormant throughout the winter, waiting for spring to return so that they can start the cycle again. Identification of its rhizomes is the perfect opportunity to directly tackle the problem with excavation and removal. Digging out and if required replacing the contaminated ground at a time when the weed is dormant, and when the garden or green areas are generally used less is a great option.

Key Facts about Japanese Knotweed in Winter

• Most identifiable signs, like leaves and flowers, are lost in Winter.
• Clustered shoots or canes remain but turn brown and brittle.
• The canes stay erect throughout the winter if undisturbed.
• The crown and rhizome of the weed remain dormant in winter.
• Winter is an ideal time to tackle the problem through excavation and removal.

Still unsure? Use our free identification service. Use the form at the top of this page to send us a few pictures of the plant that concerns you, or email your pictures to ident@knotweed.co.uk.

Japanese Knotweed Leaf Identification

Japanese Knotweed Flower Identification

 

Identifying Japanese Knotweed Roots

 

Japanese Knotweed Stems