Chinese Knotweed

Chinese Knotweed has been a problem in the United Kingdom for decades, and it is spreading to many other countries. This weed can be found anywhere from gardens to natural habitats. It is known as an invasive species that spreads quickly, which makes it difficult to get rid of.

If you have Chinese Knotweed on your property or are concerned about its presence, this guide will help you identify it and provide tips on how to eliminate the weed!

This blog post will provide an in-depth guide on what Chinese Knotweed are, how they grow, and how to eradicate them from your garden.

Quick Facts

Common names: red bush, creeping smartweed, Common Marsh Buckwheat, rice smartweed, southern smartweed, Climbing knotweed, flowery knotweed
Scientific name: Persicaria chinensis or Polygonum chinense
Family: Polygonaceae
Origin: native
Flowering season: March to November
Habitat: gardens, roadsides, industrial areas, grassy slopes, open areas, riverbanks, forest borders

Chinese Knotweed Identification

This weed can be difficult to identify, but if you notice it in your garden then it is important that you take action. The leaves and stems of the plant are very distinctive because they grow close together with a red wine colour and have a square shape.

They also possess white flowers- which unfortunately produce large amounts of seeds.

The first way you can identify if your plant is indeed Chinese knotweed is by looking at the stem. If the stems are hollow with white spots or raised bumps along with them then there’s a good chance you have found yourself some Chinese knotweed.

Another tell-tale sign will be its leaves which tend to grow in an alternate pattern (i.e., one leaf up from another). This type of growth habit typically only happens in plants of the Polygonaceae family.

It’s important not to confuse this weed for other similar looking plants such as Japanese Knotweed, Blackberry Bushes, or Horsetail Grass which all look very different than it does!

Infestation of Chinese Knotweed consuming a garden and killing all other vegetation
Infestation of Chinese Knotweed consuming a garden and killing all other vegetation

What do Chinese Knotweed look like?

Chinese Knotweed is a perennial, meaning it has leaves and stems year-round.

The plants will typically reach heights between 18in – 36inches at maturity and they’re always found growing alongside other vegetation like woody shrubs or trees.

Chinese knotweed plants can grow up to three feet per day and have the ability to penetrate into homes through cracks in walls or floors after they’ve been there for just two years.

It’s important that these invasive weeds are dealt with before they get out of control because if left unchecked, Chinese knotweed will disrupt drainage systems by clogging pipes- sometimes resulting in sewer overflow at your home

Chinese knotweed leaves alternate between each other on the stem
Chinese knotweed leaves alternate between each other on the stem

Leaves: Chinese Knotweed leaves will alternate up the stem of the vine and have distinctive greenish-brown stems and leaves with serrated edges on the leaf.

The leaves are 4-16cm long, soft and wavy-edged with a white blotch in the shape of a “V”.

Simple, alternate, ovate- to oblong-shaped entire with an acuminate apex, truncate base, 50–100 mm long and 30–70 mm wide

The leaf undersides have distinctive red veins running from top to bottom along each side of the blade.

Chinese knotweed stem in darkish red with adjoining nodes for each leaf
Chinese knotweed stem in darkish red with adjoining nodes for each leaf

Stem:  The long stem that connects the leaf node (that bears leaflets) at each joint gives this plant an appearance quite different from related species like bamboo or other true vines such as blackberry brambles because they don’t possess little stringy shoots off their main stalk).

If you’re unsure if what you’ve got is a weed or not, you can just clip a few leaves off the plant and see if they’re triangular in cross-section.

If left unchecked over time, the tall stems from old plants will eventually fall apart and create an excellent environment for future generations of knotweed.

Roots: One thing that makes this weed difficult to manage is because it has an extensive root system with deep tap roots reaching up from six feet down into the ground.

The roots terminate in deep rhizomes to help them regenerate new growth after being cut back or dug up – so removing them isn’t enough; you’ll need to treat them with herbicides such as glyphosate (Roundup).

This weed spreads by rhizomes (root-like structures). They are often found forming clumps because they spread using these rhizomes!

Clusters of Chinese knotweed flowers in white
Clusters of Chinese knotweed flowers in white

Flowers: Chinese Knotweed flowers are typically white and bloom in drooping clusters.

The flowers are held by a short pedicel at the base of which is a foliaceous, oval, sessile bract. The flowers are campanulate, small, white or pinkish in colour, 2.0 to 3.5 mm bearing 5 tepals, and 8 stamens with purple tips. Flowering normally takes between March to November.

There are many other flowering varieties in different parts of the world where Chinese knotweed grows wild – these include yellow, pink, white and red varieties.

Chinese knotweed seeds amongst the flowers at the height of summer
Chinese knotweed seeds amongst the flowers at the height of summer

Seeds: You may also notice small, greenish seeds on the stem – these will drop into the mulch below when mature plants die off during late summer.

Fertile flowers are followed by achene trigonous, 2.8–4 mm long and 2–3 mm diameter, bluish-black, enclosed by enlarged succulent, blue-black persistent perianth. The seeds are trigonous (triangular in cross-section), small 3 to 4 mm round and black.

Chinese Knotweed Seasonal Changes

As for seasonal changes, Chinese knotweed will typically grow from March until November with their leaves changing during different seasons.

From the late spring into early autumn, you will notice a significant number of large white or pinkish flowers on this weed.

In addition, there are many other flowering varieties in different parts of the world where Chinese knotweed grows wild – these include yellow, red and purple versions with different characteristics as well.

Chinese knotweed in spring with the growth of the flowers ready to spawn for another season
Chinese knotweed in spring with the growth of the flowers ready to spawn for another season

Chinese Knotweed in Spring

In springtime, you may see these plants have deep green leaves that are oval-shaped and measure about six inches long by three inches wide.

Chinese Knotweed flowers at the top of the stem prior to flowering
Chinese Knotweed flowers at the top of the stem prior to flowering

Chinese Knotweed in Summer

Come summertime the leaves will turn a darker shade of brown or purple before going dormant in autumn.

The Chinese Knotweed can grow up to three feet tall and produce white flowers in late summer or autumn during their second year.

Chinese knotweed leaves and flowers dying back in late autumn
Chinese knotweed leaves and flowers dying back in late autumn

Chinese Knotweed in Autumn

In autumn where it turns yellowish-brown to reddish-purple colours while putting out its last show before dying back for the winter months.

Chinese knotweed in autumn is a similar colour to the leaves and stems, but it does not have any distinctive features. The tall reddish-brown plants are topped with green leaves which will turn yellow as fall progresses.

These characteristics make Chinese Knotweed easy to identify from late summer through October; however, these differences can be hard to distinguish after November when the plant sheds its foliage.

Chinese Knotweed in Winter

Similar to most knotweeds, Chinese knotweed dies back but doesn’t die. The stems turn brown and become brittle over the coming months.

All leaves fall away and remain dormant until the following season.

How to get rid of Chinese Knotweed

If Chinese knotweed has been around for more than one year (or multiple years), there may not be much hope to get rid of them by hand anymore as their rhizomes will have taken root deep onto the ground, thus requiring more exerted efforts to remove.

Fortunately for those with this vine infesting their property, there are many options when it comes to controlling Chinese Knotweed removal; however, it is important to carefully read which one may be most appropriate before taking any action.

Method One – Herbicide Treatment

You can also use herbicides in the spring and autumn to kill off any new growth before it becomes a problem, but make sure you are using products that will not harm your plants around the area if they have been sprayed too close by.

These sprays should be applied when there is less than one inch of rain per week as well – so typically anytime between April-November. You may need to reapply these products more often during rainy seasons though for best results.

One way is via herbicide treatments applied over a two-year period.

Method Two – Digging it out

The best way to remove these plants is by digging them out by their crowns before taking off the leaves or disposing of them.

The best time period for removal is during late winter through early spring when Chinese knotweed isn’t actively growing from its rhizome system – this allows you more success since new shoots can easily break off and grow into new plants.

Method Three – Burning

This is another popular way people recommend using it to get rid of it because heat helps destroy cell tissue in both herbaceous matter and woody material (which means that fumes emitted will also contain carcinogens).

Chinese knotweed growing openly with its flowers about to blossom
Chinese knotweed growing openly with its flowers about to blossom

Chinese Knotweed Management

Chinese knotweed is a herbaceous perennial which thrives in moist environments and tends to grow quickly. If you’re looking for this plant in your area it will most likely be near ditches, streams or ponds with lots of shade.

Chinese Knotweed should not be composted.

Disease-free soil is a must for planting anything else in the area since debris from the old plant will still be present, so you want to make sure any future occupants of this space are not at risk.

If it’s been under three years since removal, there may not need to be as much caution because most of the rhizomes should have died off already while they were dormant during winter months.

Newer sprouts appearing after four or five years mean that these roots are more likely to survive than ones lodged deeper underground where decomposition isn’t happening quickly enough.

In Conclusion

Chinese Knotweed is a tough plant but with this guide outlining all areas for attack, we hope you’re ready to fight back against this enemy before they get too far into your garden again!

Chinese Knotweed is a very adaptable weed that grows in our gardens today and is one of the most resistant. However, using one of the products mentioned below will eliminate it.