The Tradition of Danish Eelgrass Farming

I'm Kathryn, and I am a designer/architecture student obsessed with Danish seaweed thatching. This is a tradition that goes all the way back to the middle ages, and involves a type of seagrass called eelgrass. Note that while it is technically not a seaweed, I will use the term interchangeably because historically, eelgrass was just called "tang", or seaweed.

Eelgrass harvesting was an important part of the Danish building industry in the early-to-mid 20th century, but unfortunately died out after a global wasting disease affected the harvest.

These days, washed up eelgrass is seen as waste, or a smelly annoyance rotting on the beach, but has the potential to be a really important building material for us again.

If it's harvested properly, it is rot resistant, does not smell, and can last many years as insulation in walls. It also insulates comparably with modern mineral wool, and is naturally fire resistant. It also is carbon neutral when used locally, and can absorb CO2 emissions.

I finally got to visit Møn Tang (I got a lift from a documentary team called MOOT, because I don't own a car), which is a traditional seaweed farm in Møn, to learn more about this process. It is run by Kurt Schierup, his wife Lone Schierup, and their family.

Kurt is literally the OG seaweed farmer. This is him as a little boy in 1950, farming on Tarø. Back then, there was a company called "Kalvehave Tangexport" that sold eelgrass for insulation, for mattress stuffing, and furniture upholstery. (source: Møn Tang) This company unfortunately died out with the wasting disease, but in 2016 he started Møn Tang.

The eelgrass is usually collected in the autumn season, and can only be harvested after the local municipalities give the green light. This means that most eelgrass in Denmark is not actually harvested or used, and is instead left to rot. The eelgrass that can be harvested is left onto a field to be rained on and dried. This process removes the outer salt layer of the eelgrass, and makes it rot resistant. It is then collected off the field to be turned into bales. Sometimes though, there is not a big harvest of eelgrass, because not a lot washes up. All of this is what makes farming eelgrass a big investment, and why it has not been commercially reproduced large scale anymore.

This is a traditional eelgrass presser. It is estimated to be 60-80 years old. Kurt told me that as a kid, he used to jump on top of the seaweed, so they could compress more of it into a bale.

Naturally, I had to try out the presser myself. The bales in the background are 220kg and are mostly shipped to the island of Læsø, to restore the traditional seaweed thatch roofs.

Danish seaweed thatching

This is what those traditional seaweed houses look like.

In 2013, there was an architecture project called "Det Moderne Tanghus" where eelgrass was stuffed into woolen nets and used on the facade of a summerhouse on Læsø. Eelgrass was also used in the prefabricated wall elements as insulation. They measured out the correct amount needed to keep the house warm, in each wall cavity. Photo by Realdania/Vandkunsten's book Det Moderne Tanghus.

Kurt has a replica of the knitting apparatus used for the netting of the seaweed rolls of Det Moderne Tanghus. It's on display in the barn. There are two different sizes, for the roofing and facade elements.

Kurt and Lone have turned part of the barn into a little museum that showcases historical and contemporary products with eelgrass. On the left is an old eelgrass insulation bat, called Cabots Quilt. It is actually over 90 years old, and the eelgrass is still in wonderful condition. On the right is a contemporary eelgrass batt, created by Læsø Zostera. It is naturally fire resistant, and Cradle-to-Cradle certified.

Lone Schierup makes pillows, yoga pillows, and even is experimenting with making a duvet stuffed with eelgrass. She also is creating DIY kits, where you can sew and stuff your own pillow. There are also some cosmetic products made of the eelgrass.

This was my favorite- a cute little Christmas wreath made of eelgrass. Lone pointed out to me that it's less of a fire risk than pine needles are.

Obligatory cat tax. This is Sorte Mis, and she loves pets, and loafing on seaweed. Hope you found it interesting :)