Sometimes a plant can be so aggressively invasive and problematic that people can overlook its good qualities, or refuse to believe it has any. Such is the case for Japanese knotweed, a plant so invasive that it has seemingly taken over wide swathes of the Eastern United States and elsewhere.
In Southern New England, it is hard to find a corner or roadside in cities and suburban areas that this plant hasn’t yet colonized. Across the pond in the UK, it can be difficult to get a mortgage for a home with Japanese knotweed present, since lenders are concerned about the potential structural damage the plant’s roots can cause.
However, despite all of the problems, this plant causes in municipalities and with homeowners, it does have some great uses. Since homesteaders can find it just about anywhere, you should definitely learn how to make the most of it. Here is what you need to know about Japanese knotweed.
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What is Japanese Knotweed?
Japanese knotweed (Reynoutria japonica / Fallopia japonica), also known as billyweed, elephant ears, and American bamboo, is an herbaceous perennial in the buckwheat (Polygonaceae) family.
The plant is native to eastern Asia but has become a noxious plant in North America and Europe.
This tall growing perennial is edible, and known for its sweet, lemony rhubarb taste.
However, it is detrimental to the ecosystems it takes over, and there are several efforts to being undertaken across the globe to stop its spread.
Japanese knotweed grows throughout the United States, as it can tolerate a wide range of conditions.
Although it is popular in foragers’ kitchens, it is highly invasive, and several states have launched campaigns to stop its growth. Although the plant provides nourishment for bees, insects, and birds, its medicinal benefits for humans are mostly unproven.
Japanese knotweed is a tall growing weed. It can grow as high as 10-13 ft (3-4 m). Being as tall as it is, it isn’t difficult to notice in the wild.
In late summer, the leaves and flower clusters grow incredibly dense, making the weed almost look like a thick wall of vegetation. The contrast of the broad green leaves with the long, finger-like clusters of white flowers can be beautiful, even though the plant is destructive.
Japanese knotweed stems look very similar to bamboo stems. Knotweed stems are long, hollow, and between 1-2” thick. They have raised red or purple nodes that give them the distinct bamboo-like appearance.
When the plant first appears in spring, the stems are actually red, and as the plant grows, the stems become green, with the red and purple spots at the nodes. The plant has dead, red stalks in winter.
The edible stems are tart and juicy. You’ll want to harvest knotweed in early spring, as the stems get harder later into the year.
Japanese knotweed has broad, ovate leaves. Leaves grow in an alternate pattern along the stem, one at each node. They are also quite large, growing between 3-6” long and 2-4” wide. Leaves are pointed, and almost triangular at the tips.
They have smooth edges. The leaves are a verdant green and nearly hairless, except for a few small hairs on the undersides of the veins.
Knotweed grows creamy white to greenish flowers in long, finger-like clusters. These clusters can grow up to 4 inches (10 cm) long. The clusters usually grow from a node alongside the node’s individual leaf.
The flowers themselves are very small, usually only 0.2 inches (half a centimeter) big. Flowering occurs in late summer or early autumn, usually between July and September.
They don’t last very long, as they drop in October when the plant becomes dormant for winter. However, the flowers do produce nectar.
Other Asian plants that have been introduced to North America can be mistaken for Japanese knotweed. Some of these plants, like knotweed, are considered noxious, and states have launched initiatives to control their spread. Others, however, just need to be watched closely. Two common lookalikes are houttuynia and Himalayan honeysuckle, both of which have edible components like knotweed.
Houttuynia cordata, also known as rainbow plant, Chinese lizard tail, or simply houttuynia, is another herbaceous perennial that was brought to the United States from Asia.
Like knotweed, houttuynia has broad, dark green leaves growing in alternate patterns and greenish-yellow flowers. Like knotweed, it grows in shady, moist environments. Also like knotweed, it is an invasive species that can be extremely difficult to get rid of.
If you look closely, you’ll see that houttuynia flowers are much different than knotweed flowers. Rainbow plant flowers have four petal-like bracts, and do not grow in clusters. Although they are a creamy white or greenish, they bloom in early summer, a few months earlier than knotweed. However, eradication strategies are the same for both plants.
Leycesteria formosa, known as Himalayan honeysuckle, is a tall growing, deciduous shrub. This shrub can grow up to six feet tall, shorter than knotweed but still quite tall. It also has large leaves and clusters of flowers that last until September. However, it is more easily distinguished from knotweed than houttuynia.
Himalayan honeysuckle’s flower clusters are sometimes white but can also be dark red or green. The honeysuckle’s leaves also grow in an opposite pattern and have serrated edges. Although the plant is considered noxious in Australia, it has not been classified as such in the United States.
There is some concern about it, because of the rhizome system of spreading, but it is not considered a problem like knotweed, and can still be grown in gardens, so long as proper care is taken to control it.
Japanese knotweed is present in 42 out of 50 states. It is also growing in 8 out of 10 Canadian provinces. The only regions it hasn’t been able to spread are the arid southwest, the Rocky Mountains, and the gulf coast. However, the plant has spread like wildfire throughout the rest of the country.
Japanese knotweed is an incredibly hardy plant, otherwise it couldn’t have spread across North America as it has. The plant is known to grow in hardiness zones 4a through 8b. This means it can survive low winter temperatures between -30℉ (-34.4℃) and 15℉ (-9.4℃).
Japanese knotweed prefers moist soils in sunny areas. You can usually find the plant growing in low lying areas and along waterways, such as rivers, streams, and creeks.
Although the plant thrives in wet environments, it can be found in a wide range of soil types. This plant is ultimately not too picky about moisture levels or pH unless the soil is extremely dry. The plant also grows better in sunlight than in shade.
You can often find it growing along roadsides or infesting cultivated land; it will establish and soon become a problem in homeowners’ yards if they are not careful as well. Even though it is less robust in shade, the plant often grows in woodlands, frequently taking the areas over and crowding out other less robust native plants.
Japanese Knotweed is native to Japan, China, Taiwan, and Korea. This Asiatic perennial was first introduced in the UK in 1825 as an ornamental garden plant. Sometime in the late twentieth century, it was introduced in North America.
The plant has since spread to 42 out of 50 states. It is considered a noxious weed in most states. Since it grows so tall and wide, it often blocks sunlight that lower vegetation needs to survive.
Knotweed spreads via a system of underground rhizomes. Rhizomes commonly split, and the splintered roots can grow their own functional knotweed clones. Furthermore, knotweed often spreads noxiously in wet areas.
Waterways disperse the roots, which can settle and grow knotweed wherever it lands throughout an ecosystem. Many people have tried cutting the stems to stop the spread, but it will regrow as long as the roots are intact.
Government officials in the United States, Canada, and even England have had to take measures to control knotweed growth. Solutions range from mechanical, to chemical, to biological.
While you could spend years digging up rhizomes to eliminate knotweed, wildlife officials recommend the use of certain herbicides over a long period of time.
In some cases, wildlife officials have released insects who eat knotweed, but this is a government response, and individuals should not release foreign insects into environments.
If your yard has a knotweed infestation, it could take years to get rid of the plant. However, regular cutting and use of herbicides will allow you to control the weed. Use a glyphosate concentrate for the herbicide.
Start on a dry day by cutting the stem and immediately spraying the herbicide. Wait seven days before cutting again, as you have to give the herbicide time to spread.
You can use this message again in early fall to control growth. However, if your homestead is organic, or you shun the use of herbicides, you can use other means to eradicate this plant.
Another method to address knotweed is by smothering the plants. Smothering will enable you to remove knotweed without the use of any chemicals on your homestead.
Cut down the Japanese knotweed stems as close to the ground as possible and then remove them (they make a great addition to your compost pile). Then, blanket the area with carps, ensuring that they are secured and will not move in strong winds.
Leave the tarps there for from summer until the next growing season, and it should be enough to smother the plants and kill the roots.
Some governments have resorted to introducing insects or pathogens into knotweed habitats to destroy the plant. Through 2000-2013, several wildlife agencies studied the effects of Japanese knotweed on native plants, and the efficacy of introducing insects that fed on knotweed in controlling it.
The European Union approved the introduction of the Alphara itadori, or Japanese knotweed psyllid, to control knotweed growth. Studies in England and Wales found that the insect was effective in limiting knotweed growth and did not breed on 90 near native species.
Thus, the insect can control knotweed without becoming a pest itself. You should contact your local agriculture extension office to see if there are any options for knotweed control like this in your area.
Young knotweed stems are edible. They are known for having a sweet, lemony-rhubarb flavor. In the plant’s native Japan, the plant is eaten as sansai, a wild foraged vegetable.
The plant is not cultivated in gardens, likely because of how quickly it spreads. However, it can be found abundantly in the wild for those who want to cook it.
It’s quick and easy to make a puree out of the young shoots of Japanese knotweed.
- Chop the shoots into small, one-inch pieces.
- Throw the chopped shoots into a deep saucepan and add 1½ cups of sugar and ½ cup of water.
- Cook for about 15 on medium heat.
- Once the knotweed is completely soft, transfer the mixer to a blender, and puree at a high speed.
- Puree until the mixture is very smooth.
You can keep the mixture in a jar in the fridge or freeze it.
Japanese Knotweed Pie
If you’re looking for something sweet, try making a strawberry-knotweed pie. The knotweed is a fresh substitute for the usual rhubarb.
A quick and easy way to use your puree mentioned earlier is to make knotweed bread. Sift the flour, sugar, baking powder and salt into a bowl. In a separate bowl, beat one egg, and add sunflower oil, honey, and orange juice.
Add walnuts (optional) and the knotweed puree to the dry ingredients. Then, add the wet ingredients, and mix until everything is just moist. Spoon the mixture into a greased bread pan, and bake for about one hour at 350℉ (177℃).
You can also make knotweed pickles for a crunchy snack. Here is a great video that discusses (to song!) how to make tasty knotweed and peppermint pickles:
While the health benefits of knotweed on humans remain unclear, one thing scientists have noticed is that Japanese knotweed can be beneficial for wildlife.
Although the weed destroys other plants, creating a monoculture, ecologists have found that bees, insects, birds, and even otters all find important uses for the plant. And it’s worth noting that if Japanese knotweed shows up in your garden, it is not harmful to pets, even if removal is a long process.
While knotweed harms other plants, it has proven to be very beneficial for bees and other insects. The creamy white flowers bloom between August and September.
These flowers contain nectar, which is an important source of nourishment for bees in autumn. Some beekeepers prefer that their bees feed on knotweed nectar, as it gives a buckwheat flavoring to the honey they produce.
Every autumn, knotweed drops seeds. These seeds are very small, dark, and triangular. Scientists have noted that the seeds are not viable, and the plant mainly relies on rhizomes to spread.
However, these seeds serve one important purpose. Birds eat them in autumn. Billyweed seeds provide birds with important autumnal nutrition before migration, just as billyweed nectar provides autumnal nutrition for bees. Additionally, birds can build nests in the dense vegetation.
Knotweed is delicious but should be harvested from the wild rather than grown in a garden. But when you go foraging, you must still practice caution. Pieces of knotweed as small as 1cm can take root and continue the noxious weed’s spread.
If you are foraging for stems, be very careful not to drop any pieces of the plant you collect. If you are foraging near water, be careful that no parts of the plant get into the water.
Additionally, try not to just walk casually through a stand of Japanese knotweed, either. Even knotweed parts that get stuck to your shoe and unstuck in another area can take root wherever they are dropped, furthering the spread.
Finally, if you notice knotweed beginning to grow in your yard, contact local experts right away, as it is much more difficult to control fully grown knotweed.
Parting Thoughts: Putting an Invader to Work on your Homestead
There are few introduced plants in the United States that are as invasive as Japanese knotweed, and governments at all levels are expending money and effort to control its spread.
However, while you do your part to keep knotweed from taking over the world, you should also put the plant to good use as well. It is delicious and versatile, and can be a great addition to your kitchen and diet.
So, go find some knotweed; it shouldn’t be too hard to do. Then, once you’ve located a stand, carefully harvest some, and put it to use in your kitchen or diet today.
When Tom Harkins is not busy doing emergency repairs to his 200 year-old New England home, he tries to send all of his time gardening, home brewing, foraging, and taking care of his ever-growing flock of chickens, turkey and geese.