Japanese knotweed - Reynoutria japonica (Taxonomy, Characteristics, Flower, Images, Control)

Japanese knotweed

Also known as: Fleeceflower, Elephant ears

Hearing the name of japanese knotweed can strike fear in the heart of homeowners. When this aggressive and invasive weed is identified on a property, mortgage lenders sometimes deny loans or demand extensive chemical treatment. This is due to the fact that the root system of japanese knotweed is so extensive that once established, it can be nearly impossible to eradicate.

Scientific classification

Species

Japanese knotweed (Reynoutria japonica)

Pinks, cacti, and allies

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Weeds

Weed or not

Perennial

Lifespan

Herb

Plant Type

Summer, Fall

Bloom Time

Fall

Harvest Time

1 m to 2 m

Plant Height

90 cm to 6 m

Spread

Green, Blue, Red

Leaf Color

2.5 cm

Flower Size

Cream, Brown, Tan

Fruit Color

White, Yellow, Green, Cream

Flower Color

Green, Red, Brown, Burgundy

Stem Color

Winter dormancy

Dormancy

Deciduous

Leaf type

5 - 35 ℃

Ideal Temperature

Summer, Fall

Growth Season

Rapid

Growth Rate

Images of Japanese knotweed

Distribution of Japanese knotweed

Distribution Map

The japanese knotweed plant has a distribution range that includes parts of East Asia and Russia, where it grows in sunny areas with disturbed soil. It is an invasive species in other countries, including most of the United States, where it pushes out native plants.

Native

Cultivated

Invasive

Introduced

No species reported

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Habitat

Forests, Humid areas, Wetlands

Hemisphere Trend Curve

Northern

Sorthern

Culture

Garden Use

Originally introduced in some areas as a garden ornamental, japanese knotweed is considered an invasive weed in some nations. If you are planning on planting this attractive plant, check your local laws and by-laws first. When planting, keep it away from foundations as its root system can cause damage to structures.

Symbolism

Binding, Health, endurance, hope

Interesting Facts

Japanese knotweed is considered such a feared invasive species that in the United Kingdom, it has affected the real estate market. In 2012, several mortgage lenders were reported to have denied mortgage applications due to japanese knotweed being discovered on the home's property or on neighboring property. Since the report, many institutions have lobbied to relax lending restrictions based on the presence of japanese knotweed, arguing that it can be treated and controlled.

Name Story

Japanese knotweed: If you see this plant in a garden or yard, you must be careful. It is listed by the World Conservation Union as one of the most critical invasive species in the world. It is originated from Japan. The most obvious feature is that it has hollow stems and obvious protruding nodes like bamboo, so it is called Japanese knotweed.

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Toxicity

Japanese knotweed contains oxalic acid in its stem and leaves, leading to mineral deficiency when over-consumed. Excessive intake can worsen rheumatism, kidney stones, hyperacidity, gout, and arthritis. Other Reynoutria species may cause extreme UV sensitivity after consumption.

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Weed Control

Native to East Asia in Japan, China, and Korea, japanese knotweed has established itself around the world. The World Conservation Union lists it as one of the world's most invasive species due to its aggressive root system and its ability to completely take over environments – so much so that in the UK and Scotland, it is actually illegal to plant or grow it. Japanese knotweed can damage all manner of modern architecture, from roads to foundations to buildings. Its roots grow so deep and re-sprout so vigorously that removing japanese knotweed is nearly impossible.

How to Control It

The best season for the removal of japanese knotweed is late summer to early autumn, specifically, before the plant transitions into its winter dormancy stage. This timing is crucial because it corresponds to the translocation of nutrients within the plant, which allows any applied treatments to be more effective. Here are some methodologies for its control:

Digging: Firstly, make sure you have protective gardening gloves and a shovel. Start by digging around the plant, aiming to remove as much of the root system as possible. Ensure to dispose of all parts of the plant in a responsible way to prevent any regrowth.
Smothering: This is a less labor-intensive, yet equally effective method of control. Firstly, cut the japanese knotweed down to ground level. Then, cover the area with cardboard or a thick layer of newspapers, followed by a generous level of mulch. The covering will block light and choke out the plant, eventually killing it.
Biological Control: This involves introducing a pest or disease that specifically targets japanese knotweed, such as the psyllid insect, Aphalara itadori, used in the UK. Keep in mind that this method requires careful planning and implementation to ensure the balance of your local ecosystem isn't negatively affected. It's advised to consult with a local horticulturist or ecologist first.

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Quickly Identify Japanese knotweed

Heart-shaped green leaves with rippled edges, up to 6 inches (15 cm) long.

Hollow bamboo-like stems, 6 to 9 feet (2 to 3 meters) tall.

Small creamy white flowers in branched clusters during late summer.

Distinct triangular-shaped dark brown to black fruit with winged achenes.

Large, hollow, jointed stem with mottled pattern resembling bamboo, reaching up to 10 feet (3 meters).

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Care Guide for Japanese knotweed

Every week

Water

Full sun

Sunlight

5 - 35 ℃

Ideal Temperature

Water: Thriving in humid environments, japanese knotweed balances moisture retention with drought resilience. It needs moderate hydration, ideally watered weekly and prefers consistent soil moisture without waterlogging. As a perennial herb, consider natural rainfall in its watering routine during the vigorous growing season.

Propagation: Propagate japanese knotweed in spring and autumn via division. It is moderately challenging, requiring soil remoistening. Success is marked by new growth. For optimal results, divisions should include both roots and shoots.

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Images of Japanese knotweed

Distribution of Japanese knotweed

Culture

Toxicity

Weed Control

Quickly Identify Japanese knotweed

Care Guide for Japanese knotweed

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