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Japanese Knotweed

Weeds are notorious plants that have gotten a long-time bad rap for their invasive nature and tendency to take over home gardens, farms, and other landscapes. However, we might have found just the weed to change these opinions.

While it’s often seen as a pesky annoyance in your yard, the Japanese knotweed has many health benefits and healing properties used throughout generations. It’s even a tasty ingredient in certain cuisines!

Keep reading to learn all about Japanese knotweed, including how to identify it, its dangers, benefits, methods of spreading, and how to eradicate them.

Closeup of white flowers and heart-shaped leaves of Japanese knotweed.

How To Identify Japanese Knotweed

When young, these leaves are tightly rolled up and have dark red veins. The Japanese Knotwood leaves can grow up to eight inches long as they mature.

The Japanese Knotweed is identified by clusters of cream-white flowers that bloom in the late summer months. Its light green leaves are heart-shaped and spotted with red and purple flecks.

This plant typically grows upwards and can reach heights from seven to nine feet. The stems grow in a zig-zag pattern and rapidly increase in height each day, especially in late spring and early summer.

The weed produces seeds that, like the leaves, are heart-shaped and feature small wings. The roots of the Japanese Knotweed have a dark brown exterior with a yellow interior and can grow nine feet deep into the ground.

Closeup of the stems of Japanese knotweed.

What Makes It a Weed

The Japanese Knotweed is classified as a weed because of its large system of underground stems and ultra-invasive nature. They form dense colonies that compete with vegetation for natural resources that result in the death of domestic flora.

Where it Came From

Contrary to its name, the Japanese Knotweed is native to not only Japan but also China, Korea, and Taiwan.

It was brought to the United Kingdom, from Japan, as an ornamental plant in 1825, followed by its delivery to North America towards the end of the nineteenth century.

Problems Created by Japanese Knotweed

View of the banks of a creek or river overrun by Japanese knotweed plants.
Banks of a creek overrun by Japanese knotweed.

Environmental Damages

Because of its competitiveness and ability to spread rapidly, the Japanese Knotweed is extremely harmful and detrimental to surrounding nature.

It has a tendency to form clusters, which contributes to its dangers. This causes the weed to block sunlight from surrounding plants and rob nutrients and water from the soil, leaving them to die.

The Japanese Knotweed also releases chemicals from its underground stems that suppress other plants’ growth and hinder their ability to germinate.

This weed can also reside in wet habitats, creating even more problems. If located by a river shoreline, for example, the Japanese Knotweed can make its way into the water and be taken by the current. As it populates, it will begin to impede water flow which increases the risk of floods throughout nearby cities. If the water can’t flow properly, it’s likely to back up and overflow into nearby land, resulting in these damaging floods.

Closeup of Japanese knotweed vines.

Structural Damages

This weed is not just dangerous because of its harm to other plants. The Japanese Knotweed can also cause structural damage to its surrounding areas. When found close to man-made structures, the rhizome (or underground stems) can weaken the integrity of and destroy roads, sidewalks, parking lots, and much more.

As more pressure is exerted, the Japanese Knotweed can split structures from their weakest points and can even damage underground conduits and septic systems, causing devastation throughout cities.

How It Spreads

Closeup of white flower of Japanese knotweed.

Like many other invasive species, the Japanese Knotweed spreads mostly by its seeds and stem fragments. The seeds can be transported by wind, animals, water, humans, or soil and cause widespread growth.

This weed also is spread through its rhizomes. As they are dispersed, they produce sprouts of shoots that can be unknowingly transferred to new locations to continue their growth into the mature plant.

How to Get Rid of It

The best method of controlling the prevalence and spread of Japanese Knotweed is through a combination of cutting the plant and using herbicides.

Treatment is most effective when done in the late spring or early summer and is followed by re-treatment in early fall. It may take several years of treatment to eliminate well-established colonies, so patience is key.

The best herbicide option is a glyphosate-based weed killer. It’s most effective when applied to cut stems so the chemical properties can thoroughly penetrate the roots.

If you’re struggling to get rid of these pesky plants, check out this grass and weed herbicide from Tractor Supply Co.

Health Benefits of Japanese Knotweed

Believe it or not, this weed has been used for centuries by herbalists for a wide range of medicines and treatments.

It has been used to reduce plaque, gum pain, and gingivitis. The whole flowering plant has also been a key ingredient in medicines to help reduce respiratory ailments by reducing inflammation of the lungs, cough, sore throat, and more.

An alcohol tincture made by steeping leaves of Japanese knotweed.
Tincture made with knotweed leaves.

Not only does it provide medicinal qualities, it is also rich in vitamins and nutrients. The Japanese Knotweed provides a significant amount of vitamins A and C, potassium, manganese, phosphorous, and zinc.

How to Use This Weed

Not only does Japanese Knotweed make a great nutritional supplement, but it is also a tasty ingredient that can enhance many culinary dishes. Here are a few ways you can use it in your kitchen and reap its many benefits.

What it Tastes Like

The hollow stems of this plant are segmented like bamboo and have a flavor almost identical to rhubarb. They provide a crunchy, juicy, and tart taste that allows them to be eaten raw or cooked.

Japanese knotweed shoots on a cutting board.

Because of this unique flavor profile, they can also be made in sweet and savory recipes.

The leaves of the Japanese Knotweed are also edible and can best be described as tasting like a cross between asparagus and rhubarb.

Using the Leaves

These leaves make a great addition to a multitude of recipes, including jams, sauces, soups, and smoothies. Its rich source of vitamins and minerals gives an extra boost to your daily diet.

Try blending the Japanese Knotweed leaves into this Veggie and Blueberry Smoothie. You can choose to supplement the current ingredients with extra greens or replace the spinach with this nutrient-dense plant.

Using the Shoots

Japanese knotweed shoots growing wild.

In the spring, the shoots of the Japanese Knotweed are tender enough to be eaten, as long as you gather them before they become too woody (ideally in May). Make sure to peel the shoots, and enjoy them pickled, grilled, raw, sauteed, and more.

For a sweet and nutritious treat that can be enjoyed on the go, you can turn this ingredient into a Japanese Knotweed Fruit Leather. With the addition of sugar, water, and a little bit of cooking, this recipe is perfect for sneaking a bit of extra health into your kids’ favorite snack.

If you’re into savory foods, these Summer Rolls are light, fresh, and full of flavor. This recipe is not only tasty, but it’s also fun to make!

More Than Just an Invasive Plant

White flower buds on a Japanese knotweed plant.

Although it brings about challenges, the positive qualities of Japanese Knotweed are vast and should not be overlooked when learning about this plant.

If you ever face this invasive species, make sure you reap some of its benefits before getting rid of it!

If you feel like you need to learn more about these pesky garden tenants, check out our weeds page to learn all about different weed varieties, treatment options, and surprising information.