Harm Jagerman

Thank you Philipp Franz von Siebold!

He was one of the first Europeans to teach Western medicine in Japan in the nineteenth century. Philipp Franz von Siebold loved plants and flowers. He loved them so much, that he decided to take many specimens with him to The Netherlands. Amongst those plants and flowers: the Japanese knotweed. Thank you, Philipp Franz von Siebold, for introducing this invasive species into the western world.

Phillip Franz von Siebold
Phillip Franz von Siebold.
Image source: Wikimedia.


Eventually, Japan wasn’t that friendly for Von Siebold, as he was expelled from the country. He was accused of espionage because he was given charts of Japan as a gift. In 1829, he was forced to leave the country.

It was because of Von Siebold that people got to know the hydrangea or Hortensia. When first arriving in The Netherlands he planted them into his greenhouse (Nippon) and via the Leiden Hortus Botanicus, the plants made their way across the country and probably the rest of Europe. Who doesn’t know this plant? Pink, white, blue. In my own backyard, this plant also grows. I once dug the plant out in the garden of some lady who didn’t want it anymore. Then I felt like Von Siebold. He too brought plants and flowers from other places to his garden.

The azalea or rhododendron was also transported to The Netherlands. Just like the hosta. These are all just fine and beautiful specimens. One ornamental plant that Von Siebold brought to the western world wasn’t that beautiful. It was just some case of bad tares. Tares with a devastating effect. This was the Japanese knotweed, also known as Fallopia japonica or Asian knotweed.


I fear the day when I notice that this plant grows in my own garden. A few years ago we had trouble getting rid of another oriental plant: bamboo. It was the roots of this plant that caused the trouble, just like the Japanese knotweed does. When cutting off the stems of the plants, the roots keep on growing. The Japanese knotweed is notorious because its roots can grow through concrete. You can cut off the stems, but the plant isn’t stopped. Nowadays the Japanese knotweed grows everywhere in Europe, not just The Netherlands.

Thank you, Philipp Franz von Siebold!

Thank you, Philipp Franz von Siebold, for introducing this invasive species to the western world! Still, it wasn’t the only invasive species that was introduced in history. Take for instance the aquatic plant Cabomba. This plant is used inside fish tanks. It makes sure there is enough oxygen in the water, making the water better for the fish. Unfortunately, some dreadful day someone decided that the wanted to get rid of their aquarium and flushed it through the toilet or emptied the contents of the aquarium into open water. From that day on, Cabomba started growing in the Dutch waters. Whoever is responsible for this remains anonymous. The plant forms a threat to the plant- and wildlife in the Dutch waters. The plants grow very fast. Probably faster than the location that they originate from: South America.

Rose-ringed parakeet

Some plants and flowers arrive unintentionally. They are ballast or “stowaways” of ships. This doesn’t apply to plants and flowers. Several animals have been introduced into the western world. Sometimes intentionally, sometimes not. The best-known example in The Netherlands is the rose-ringed parakeet. Birds such as these don’t have natural enemies and have adjusted to the sea climate. Other examples of exotic animals that made their way to The Netherlands and the rest of the western world are the muskrat, procambarus clarkia (cambarid freshwater crayfish) and the harlequin, multicoloured Asian ladybeetle (Asian ladybeetle).

Rose-ringed parakeet
Rose-ringed parakeet.
Image source: Wikimedia Commons.


Funny story about the rose-ringed parakeet: it is believed that these birds were set free one of the major parks in Amsterdam (Het Vondelpark) by a city biologist. I wasn’t able to find any evidence for this. The first birds that moved freely might have escaped captivity. These birds aren’t the only ones who are able to adept. Take for instance the seagull. This bird isn’t only to be found at or near the coastline. Well, the seagull isn’t the best example though, since this animal has been living here for centuries.


What to do about the nuisance caused by these animals? We can place fences all over the country. This has been done in parts of The Netherlands to prevent wild boars from leaving the natural area known as De Veluwe. Unfortunately, birds aren’t hindered by fences. This is the same for everything that lives in the water. There are other options to consider. The Dutch television news (NOS) compiled an article about the Japanese knotweed and you can see an example of the usage of Japanese knotweed: turning it into beer. Well, one solution could be – when it comes to Japanese knotweed – is to drink more beer… 

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