return to projects

Rhubarb Leaves: Dye and Mordant

June 23 2026

The only reason why I learned about the fact that you can dye (and mordant!) with rhubarb leaves is because of some lupins growing along the edge of train tracks. On the way to a small cabin in Stockholm County, I saw some lupins at Hemfosa station. There were quite a lot of them and I hadn't really seem them growing elsewhere, so curiosity struck and I learned that you can dye with them!Within my first couple searches regarding dyeing with lupins, I read about how someone mordanted their wool skeins with rhubarb leaves here.

Mordants are dye fixatives that help natural dyes bind better to natural fibers, such as wool! I was literally shocked because there is quite a lot of rhubarb in Sweden (or really just the people I know?) that people grow in their backyards. Rhubarb leaves are typically thrown away or composted because they contain oxalic acid, which can damage your kidneys and can cause death in high amounts. I'm sure there are other potential uses for them but this is just what I have experienced. I had also just had several rhubarb treats, such as rhubarb sauce and rhubarb pie, so as you can imagine, I was quite shocked to hear that the leaves could be used for something. Additionally, I was lamenting how I would be mordanting my wool for my projects as I wasn't sure where to get aluminum acetate or iron powder...? (idk I'm not a dyer) and I didn't particularly want to purchase things online. Sourcing locally and foraging would help reduce transportation footprint and costs anyways.

During Midsummer, I was given the chance (haha) of seeing an insane rhubarb plant that was probably like 40 years old. It was humongous and even had several rhubarb flowers, which tends to only show with older, mature plants. The family didn't really eat rhubarb (or do much with it I think), so it just sat there! With the amount of rhubarb leaves within reach (through permission and family connections) and some simple research, I figured I had to start my summer dyeing with a vat from rhubarb leaves.

~ ~ ~

To start off, I collected the leaves of the rhubarb, leaving the stalks to be cooked and eaten at a later date. You want to weigh the leaves, with mine being at 780g.

Chop up the leaves and add them to your dyepot! If you don't know this already, you typically don't want to use your dyepot for food after using it for dyeing. I thrifted a pretty big pot earlier this summer with the intention of using it solely for dyeing! I filled the pot with hot water, enough to cover the leaves in the pot. I brought it to a boil on top of the stove. Normally, you may want to do this outside as oxalic acid is toxic, but a well ventilated area works well too.

The moment I started boiling the leaves, there was a pretty strong smell so I made sure to open several windows to air out the room. Now, this site recommends you cooking the leaves at approximately 180°F or 80°C but umm I also didn't have a tool for measuring that, so I just let it boil and simmer somewhat for an hour. Is that super important? I have no idea really but this summer is all about testing anyways. I stirred the leaves every 10-15 minutes.

After an hour, I removed it from heat, and let it sit outside on a table for a couple hours while I got groceries. Once it was cool and I was done with my errands, as I didn't have a strainer (yet) I removed the leaves by using a cooking spoon with holes that I thrifted two days ago. Tossed it into the woods as it was compostable anyways.

Onto using this mordant for projects! It seems like you can also use this as a dye liquid, though as most plants out there, your yarn will likely just turn yellow.

~ ~ ~

Note: July 4, 2026.
I will say that after a week and half or so of leaving this mordant alone, it did mold. Based on what I've read online, it should be fine to just skim the mold off and use the mordant as you would! Will post another update once my yarn is out of the mordant pot to show the potential dye color you can get from rhubarb.