Japanese Knotweed Symposium

Lets talk Japanese knotweed!

14 Apr 2023
15 Apr 2023

Mediamatic invited experts and creatives from various disciplines to discuss all things Japanese knotweed. We will unpack the plant that is so often described as invasive. The symposium focussed on how we can re-imagine the knotweed and investigated gateways towards the plant becoming a future companion, rather than enemy. 


Seminar Japanese Knotweed Festival -

Friday 14th of April

Block 1: Introducing the Invasive Exotic

Get to know the invasive exotic, as a newcomer, as a threat or as a part of our environment.

Introduction by Willem Velthoven

10:00 – 10:15

Willem Velthoven, one of the directors at Mediamatic, will kick off the symposium with an opening word about the motivation behind the festival and his relationship with the plant

Johan van Valkenburg (NVWA)

10:20 – 10:50

Johan van Valkenburg is a Senior Scientist at the Netherlands Institute for Vectors, Invasive plants and Plant health (NIVIP) of the NVWA, leading research projects relating to invasive non-native plants. In his talk he will explore how decisions regarding the management and control of 'invasive exotics' come to be, and in what way knowledge is communicated to various actors.

Remko Andeweg (Bureau Stadsnatuur)

10:55 – 11:25

Remko Andeweg works as an urban botanist at Bureau Stadsnatuur, which is a part of the Natural History Museum Rotterdam. He will talk about his observed shift in the urgency to control Japanese knotweed, and he will touch on the plethora of techniques that are used to control or exterminate the plant.

Sus Willems (Duizendknopen ontward)

11:30 – 12:00

Sus Willems worked for the Environmental department of the Flemish government, and recently started  an ecological consultancy company 'Duizendknopen Ontward'. In his presentation he will describe the differences between the Dutch and Flemish management styles of urban Japanese knotweed control. He will present ecological control methods that are focused on keeping the plant in check by introducing other (plant) species.

Lunch break: 12:00 – 13:00


Block 2: Responding to Japanese Knotweed

How can we respond to Japanese knotweed? A collection of diverse and innovative approaches, both philosophical and practical.

Anke Wijnja (The Nature Connection)

13:00 – 13:30

Anke Wijnja is a forager, nature coach, mindfulness trainer, bushcrafter and craftswoman. She works from sustainable incubator 'De Ceuvel' in Amsterdam Noord. In her work she explores why some plants are celebrated and other plants are contested. She will shine new light on Japanese knotweed by diving deeper into its culinary, medicinal, and nutritional properties. A perfect story for after lunch.

Gjalt Jan Feersma Hoekstra (Agriton)

13:35 – 14:05

Gjalt Jan Feersma Hoekstra (Agriton Group) has been active as a consultant for sustainable solutions in Agriculture for over a decade. His Dutch company Agriton Group, has brought the Bokashi concept to the Netherlands. In his talk he will describe the Bokashi concept, and help us make an informed decision whether Japanese knotweed 'waste' can be processed with Bokashi into a valuable product.

Norbert Peeters (Universiteit Leiden)

14:10 – 14:40

Norbert Peeters is a botanical philosopher, writer, and PhD-student at Leiden University. He will take us on the historical journey of knotweed in the Netherlands, and he will investigate the sudden shift in the way Japanese knotweed is publically valued. His talk may not only teach us new things about this contested plant, but also about ourselves.

Tea break: 14:45 – 15:15


Janny Vos (CABI)

15:20 – 15:50

Janny Vos manages a Dutch office of the Centre for Agriculture and Bioscience International (CABI). CABI’s scientists have carried out extensive research into the biocontrol potential of an insect and a fungal pathogen that target knotweed. Janny Vos is involved in this research, and will give us an insight into their progress.

Jaike Bijleveld (Amsterdam Municipality)

15:55 - 16:25

Jaike Bijleveld is in charge of controlling knotweed in Amsterdam on behalf of the municipality. She will talk about their strategy, concerns, and current developments. Is there space to celebrate this persistent plant?


16:30 – 17:00

The first day of the symposium will be rounded off by a panel discussion led by Nout Verhoeven, director at the engineering office of the Amsterdam municipality. In a colourful discussion Johan van Valkenburg, Sus Willems, Norbert Peeters, Janny Vos, Jaike Bijleveld and Debra Solomon will give their final take on how we should interact with knotweed. By uniting these different perspectives, we invite you to ask yourself the same question.


Japanese Knotweed - 8 tips of Japanese Knotweed shoots - Japanese Knotweed for the city Amsterdam is a big problem. The plant seems to disapear in the winter, but once is spring it comes back ever larger and stronger. It looks beautiful above the ground but underneath the plant is living a solo life. It is said to damage cables, local ecology and infrastructure. MediaMatic sees an opportunity to embrace the monster and turned it in a beautiful alternative. These thick juicy heads of the young knotweed shoots are great to cook with. Slightly… Willem Velthoven

Saturday 15th of April

Block 3: Growing Companionship

Let's talk about knotweed in our built environment and how we can inhabit the city together. 

Introduction by Willem Velthoven

10:00 – 10:15

Mas Jansma (UVA)

10:20 – 10:50

Mas Jansma is a biology student at UVA. He performed a research project centering around the genetics of the knotweed populations in Amsterdam. He will explain how he relates to the plant as a researcher, and will show that we may not know 'our neighbour' as well as we thought.

Edwin Keijsers (Wageningen University & Research)

10:55 – 11:25

Edwin Keijsers has been working as a researcher at Wageningen Food & Biobased Research for the last 27 years, and is involved with the European project CityLoops. His work revolves around extracting and processing natural fibres for optimal use in circular industrial processes. During this symposium, he will explain how Japanese knotweed could be used to replace non-renewable materials.

Gaja Mežnarić Osole, Danica Sretenović & Sebastjan Kovač (Krater)

11:30 – 12:00

Krater is a production space for a variety of practices such as papermaking, woodwork and myco-design located near the city centre of Ljubljana. Taking the regenerative capacities of pioneering species as its inspiration, Krater is set to produce environmentally conscious materials, practices and alliances.

Lunch break: 12:00 – 13:00


Block 4: Art/Design research

Artists and designers look at the ways at which we can work and live with Japanse knotweed.

Raphael Jaschko (Neo Flutes)

13:00 – 13:30

Raphael Jaschko is a musician and craftsman from East Bavaria, Germany. He will talk about the difficulties and the beauty of crafting with knotweed, show the different instruments that he has crafted, and delight us with a live flute performance.

Why Knot Design

13:35 – 14:05

Why Knot Design is set to turn a hated plant into a beloved product. They will show the beauty and potential of knotweed as a degradable and reusable material.

Introduction Festival participants

14:10 – 14:40

Some of the artists will present their research through workshops at a later stage of the festival. Get to know them and their work, during a short presentation round.

Uno Fujisawa & Takako Hamano
Lucie Havel

Pauline Wiersema

Not in My Backyard

14:45 – 15:15

Niek & Kristof will take you on a walkthrough of their exhibition 'Not in My Backyard'. 


Tea break


Exhibitions opening

16:00 – 18:00

The second day of the symposium will be closed off with a celebratory opening of the several exihibitions of the Japanese Knotweed festival. Get to know the artists behind the exhibitions and take a look at their work. From 16:00 the artists will give a quick presentation about their work, and we will celebrate with drinks from 16:30 

Niek Kosten & Kristof Vrancken (Not in my backyard)

Alaa Abu Asad (The Dog Chased its Tail To Bite it Off)

Virgile Durando (Knotweed Mosaic)

Yoshinari Nikishi (Invasive Energy Harvesting: EROI Drink)

Drinks from 16:30 


Japanese Knotweed Photographic Material Research -