Have you heard of the Japanese Knotweed? It’s a nightmare for most homeowners and gardeners. It will damage your property and is expensive to remove from your garden.
The other tricky aspect is its identification— many plants are mistaken for the Japanese Knotweed.
The pesky plant varies in appearance depending on the time of the year causing further confusion to gardeners.
To help you identify Japanese Knotweed better, we have listed several lookalike plants to give you more clarity. But first, let us learn more about the plant itself.
Japanese Knotweed (Reynoutria japonica)
The Japanese Knotweed is native to East Asia, China, Japan, and North Korea. As you would expect, the species has also established itself in other habitats such as Europe and North America and is considered invasive in most countries.
The plant is a herbaceous perennial with hollow bamboo-like stems that can grow to a maximum height of 13 ft.
However, you will still be able to spot smaller plants in each growing season sprouting after a cut-down or through pavements and cracks.
The other feature of the plant is its broad oval, green leaves with a truncate base. The leaves grow about 14 cm long and 12 cm wide and appear alternately along the stem.
The stems have visible nodes. It has a cluster of tiny white or creamy flowers blooming in late summer and the beginning of autumn. The plant thrives in a variety of soil conditions and loves moist areas.
With the ideal conditions for its growth, the Japanese Knotweed will invade an area as fast as possible.
Plants That Look Like Japanese Knotweed
While eliminating Japanese Knotweed, you can do a lot wrong by going after lookalike plants that may or may not be invasive.
This section guides you through each plant’s similarities and differences to the Japanese Knotweed.
1. Bindweed (Convolvulus arvensis)
It’s one of the annoying weeds you will come across. The heart-shaped leaves make it look like the Japanese Knotweed.
The leaves also alternate through the stem, a feature typical of Knotweed. It has the penchant to wrap itself around anything available.
The plant will climb other shrubs in your garden and entangle itself with every stem, branch, and leaf at any slightest opportunity. Trouble is unwrapping the weed as it damages the soft stem and leaves of the supporting plant.
You will spot the difference between Knotweed and Bindweed in their growth patterns. Knotweed grows upright, while Bindweed is a climbing plant that seeks support by twisting around other plants.
Also, the tiny flowers of Knotweed grow in late summer, while the large pink or white flowers of Bindweed grow in early summer.
Bindweed is also a typical weed in your garden, which means you want to get rid of it. Herbicides aren’t entirely effective in eliminating them.
Go for a spot weed solution instead and apply it to the leaves. The plant will be eradicated once the leaves absorb the chemical.
The Bamboo plant forms part of the evergreen perennial plants in the large grass family of Poaceae. Its origin is not certain, but its naming is believed to be from the Dutch language.
Typical features of the bamboo plant are the internodal regions across the stem. It’s a fast-growing plant owing to the rhizome-dependent system.
While the two plants have some visual similarities, such as upright growing stems with clear nodes, their foliage is quite different.
The leaves of both plants are not similar in shape; the bamboo leaves are longer and thinner than those of Knotweed.
The stems of the bamboo plant are also much harder than that of Knotweed— you can’t snap them with your fingers.
Another difference noticeable between the two plants is that Bamboo leaves hang year-round while Knotweed loses its leaves in early autumn.
3. Russian Vine (Fallopia baldschuanica)
Thanks to its vines dotted with flowers, the Russian Vine is an ornamental plant. It’s a fast-growing plant with leaves and flowers that appear like that of the Japanese Knotweed.
It has a climbing nature and can grow up to 10 meters high.
The leaves are borne on petioles and spread up to 4cm long. However, the leaves look more arrow-shaped compared to the ones for Knotweed.
Russia Vine is also more or less like Bindweed since it needs the support of other taller and stronger plants to grow upwards.
The plant colonizes other plants in an area due to its fast-growing nature.
If it becomes a challenge in your garden, get rid of it by painting a weed solution on its base, which, when absorbed, will lead to its downfall.
4. Broadleaf Dock (Rumex Obtusifolius)
The dock is a multi-leaved plant that matures from individual tap roots and is part of the Knotweed family.
It can grow up to a height of a meter dotted with a central flower spike. The unfurling leaves alternate around the stem and looks similar to Knotweed leaves.
On the contrary, the stems of the Broadleaf Dock are shorter and more fluted than that of the Knotweed. The stems of the Broadleaf Dock are also not completely hollow.
You should see a foam-like substance when you snap them. You can get rid of Broadleaf Dock weeds in your garden using commercial herbicides.
5. Himalayan Balsam (Impatiens glandulifera)
The Himalayan Balsam resembles the Japanese Knotweed because of its hollow stem, a similar feature in Knotweed. Like the latter, it also grows fast, covering an area within a short time.
The distinguishing feature between the two plants is the leaf arrangement. Knotweed leaves grow in an alternating pattern along the stem, while the Himalayan Balsam leaves grow opposite.
One other noticeable difference is that the leaves of the Himalayan Balsam have a pink midrib; they are longer and thinner than the Knotweed leaves.
Himalayan Balsam produces large pink hooded leaves in late Summer.
6. Lilac (Syringa)
The lilac plant loves the woody areas. Most gardeners mistake it for the Japanese Knotweed because of its lush green foliage with heart-shaped leaves.
It’s a highly invasive species that retaliates when chopped back by sprouting irritating side shoots. However, you can quickly differentiate it from Knotweed because of its woody stems.
Japanese Knotweed stems are hollow and lack solid wood. Other woody plants you are likely to come across are the Dogwood and the American Elderberry.
7. Himalayan Honeysuckle
Another Japanese Knotweed lookalike you may come across is the Himalayan Honeysuckle.
The Himalayan Honeysuckle has hollow stems that could make you easily fall for them as the Knotweed plants.
Luckily for you, other differences between the two plants are easily noticeable.
The Himalayan Honeysuckle leaves grow in opposite directions compared to Knotweed leaves that alternate along the stem.
The Himalayan Honeysuckle also has pale green leaves that lack purple speckles.
It also loves seeding all over the place. During late summer, you should be able to identify it by its unique drooping white flowers.
8. Houttuynia (Houttuynia cordata)
Houttuynia is a native to SouthEast Asia and was first cultivated as a culinary herb.
Gardeners can easily spot Houttuynia by its heart-shaped leaves with small white flowers. The plant also has an orange scent.
Houttuynia grows to a maximum height of 30 centimeters and spreads through rhizomes.
Japanese Knotweed grows to 3 meters, a clear contrast between the two plants.
9. Red Bistort (Persicaria amplexicaulis)
Red Bistort is a typical garden plant that most gardeners would love to grow. The plant has a hollow stem and loves to clump together, forming thickets.
This makes gardeners confuse it with the Japanese Knotweed. But telling the difference between the two plants is pretty straightforward.
The flowers are red compared to Knotweed’s, which are usually white. The flowers of the Red Bistort show up in late summer and early autumn.
You should have pink/white clusters or bright red/purple balls on tall, erect sticks of about 10 cm.
Its leaves are also slender than the broad leaves of the Japanese Knotweed. Another noticeable difference is the semi-translucent sheath that encompasses the stem nodes.
The sheath is not found in Japanese Knotweed stems.
10. Buckwheat (Fagopyrum esculentum)
Buckwheat is a plant cultivated for its grain-like seeds. The plant has no relationship with wheat, and neither is it grass.
It is in the same family as the Japanese Knotweed (Polygonaceae). It tends to look like the Japanese Knotweed as a young sprout.
Other similarities with Knotweed are the alternate leaf arrangement and the marked nodes you will find on its stems, like Bamboo.
Regarding differences, the plant is shorter than Knotweed, growing to approximately 60 cm. Their flowers are larger, appear at the stem end, and vary from white to pink.
You want to be keen on the leaf shape as well. The buckwheat leaves are thin, long, and triangular, and their bases love clasping around stems.
11. Lesser Knotweed (Persicaria campanulata)
Lesser Knotweed is a mat-forming perennial with semi-evergreen ovate leaves. It grows to one meter with leaves that spread 8-15 cm long and 5 cm wide.
The leaves and stem tips of the plant are hairy. It’s relative to the Himalayan Knotweed – the Persicaria species.
Most gardeners confuse Lesser Knotweed with the Japanese Knotweed.
You should spot classical similarities between the two plants: hollow stems, with the leaves having an alternate arrangement.
However, differences will start to show up beginning from their leaves. Leaves of Lesser Knotweed are longer than the broad Japanese Knotweed leaves.
There is also a difference in flower size. The flowers of the Lesser Knotweed are bigger, ranging from pale to bright pink.
Lesser Knotweed is shorter in height, only growing to a maximum of 1.5 – 2 meters tall.
12. Horsetail (Equisetum arvense)
The horsetail is an herbaceous perennial native to the arctic and the Northern hemisphere. One of its standard features is the spore-bearing stem or strobili growing underground from a rhizomatous stem system.
Their highly invasive nature makes gardeners confuse them with Knotweed. Their spore-bearing stems show up in spring at an alarming rate.
The strobili die back once they have released their spores.
What follows is the emergence of green stems and leaves that have nodes similar to Knotweed.
The difference between the two plants becomes noticeable when the strobila die and new plants appear, with a brush-like growth.
These are pretty different from the Japanese Knotweed.
13. Himalayan Knotweed (Persicaria wallichii)
It’s an invasive perennial in the Buckwheat family and is native to Asia. The plant grows to 6 feet to form mounded clumps with reddish leaf stalks and stems.
Their tapering leaves are 4-8 inches long and come with a brown sheath at the leaf stalk base.
The confusion between them and the Japanese Knotweed is their hollow-like stems and leaves alternately arranged along the stem.
You can tell the difference between the two plants by closely examining the leaves. Himalayan Knotweed leaves are thin and longer than those of the Japanese Knotweed.
The stem is also thinner, growing to a max of 180 cm, typically less than Japanese Knotweed.
The plants listed above have striking features and patterns that resemble the Japanese Knotweed. Some will show similarities in the leaf shape, the leaf arrangement, or the stem structure.
Noticing their similarities could cause you some anxiety, but you have no reason to worry. What you should know are the distinctive features of the Japanese Knotweed.
These include spade-shaped leaves with a zig-zag formation, red-speckled stems, and creamy white flowers that emerge in late summer.
With these features at the back of your mind, you should be good at identifying the Japanese Knotweed lookalikes.