DIY Herbal Dyes: Fennel on Animal Fiber

wool dyed with fennel using iron mordant

Fennel offers up lovely pale yellows to forest greens, depending on the mordant and fiber you use. In this project, we’re using raw, spun wool yarn. You can use other animal fibers using this method, as well. With no mordant, you’ll get pale yellows in the Summer Wheat family. With an Alum mordant, it’ll be the same family of color except a bit more intense. If you use an iron mordant or modifier, you’ll get a darker green to forest green. For this project, we assume you’ve already applied the mordants you intend to use. If you use an iron mordant, do not add an iron modifier. For this project, we assume you know how to mordant wool using Alum or Iron.

Wool Dyed with Fennel using Alum Mordant.
Wool Dyed with Fennel using Alum Mordant.

Harvest fresh fennel tops through out summer. You’ll get the best color from fennel that’s in bloom, but the seeds, stems, and leaves offer a lot of color as well. Plan to use double the weight in plant material for each unit of fiber you plan to dye. So, for 1 pound of fiber, use 2 pounds or more of fennel tops, leaves, flowers, seeds, and stems. Be sure to create your dyebath immediately after you’ve harvested your fennel. It’s best if you use the strained dyebath within two days of creating it. It can stand in the refrigerator up to a week, but the shades you get are likely to be less clear with an older dye bath.

In this project, we’re using handspun wool yarn. Rather than hand spinning your yarn, you can use a commercial wool yarn so long as it’s free of chemicals, treatments, and dyes. Many commercial yarn companies offer a line of wool yarns for dyeing that make lovely hand-dyed skeins in the herbal dye pot. If you choose to dye your wool before you spin or felt it, you can use this same process for dyeing it. You may need to handle the fiber more carefully as you wash and rinse it, stir it in the pot, and strain it from the dye bath or mordants. Use common sense as you work with it.

Use fresh Fennel ariel parts: Stems, Leaves, and Flowers with our without seeds.


  • 8 oz. Fresh Fennel tops, including flowers, stems, seeds, and leaves, or more
  • 4 oz. Wool Yarn
  • Water to cover
  • Alum, cream of tartar, iron (optional)


  • Cutting board and knife to cut plant material
  • Non-reactive dye pot (with cover) large enough for your project, about 15 quarters for 8 ounces/200 grams of wool yarn
  • Stove or heat source in a well-ventilated area
  • Utensils for stirring
  • Hot pads or other protection from heat when handling a hot pot
  • Strainer

Procedure for Creating Your Dyebath

  1. Coarsley chop the plant material and add it to a non-reactive dye pot.
  2. Cover the plant material with fresh water and set the pot on a burner to heat.
  3. Heat to a boil, then reduce the heat to a simmer and cover.
  4. Let the pot simmer for an hour covered, then turn off the heat and let it cool still covered.
  5. Set the pot aside to steep for at least a day and up to several before you strain out the plant material.
  6. Strain the plant material before using the liquid as a dye. Store the strained liquid, now called the dye bath, in the refrigerator until you’re ready to use it. It’s best to use it sooner rather than later mainly to avoid spoilage that can introduce unwanted color due to bacteria or molds and to avoid an off-smell in your dyed materials.

Procedure for Dyeing Wool

Wool in the dye pot already taking on color.
Wool in the dye pot already taking on color.

Decide what shade you’d like in your final fiber. No mordant will produce a light shade of yellow. Alum and cream of tartar mordant will produce a darker or more intense shade of yellow. Iron mordant will produce greens. Iron added to modify the dye bath at the very end will produce a darker shade of forest green on alum mordanted wool.

  1. Mordant your wool as appropriate.
  2. Add soaked or thoroughly wetted wool to your cooled fennel dyebath.
  3. Cover and gently heat the dye and wool in a pot over medium heat to the scald point, around 180 degrees Fahrenheit or the point where the water just begins to steam but doesn’t simmer and no bubbles form.
  4. Hold the pot at the scald point for at least an hour, then turn off the heat and let the covered pot cool.
  5. Set the pot aside where it can stand for several days. Monitor the color as it stands. When it’s as intense as you like or as you believe it will become, add your iron modifier if you plan to use one and let it stand another 30 minutes to an hour then remove the wool. Or, if you don’t intend to use an iron modifier, remove the wool at this point.
  6. Carefully squeeze the dye from the wool, then wash out excess dye.
  7. Submerge the wool in a water bath that’s about the same temperature as your wool with a very small amount of gentle laundry soap, let it stand a moment, then remove it and squeeze out the water.
  8. Submerge the wool in a plain water that’s about the same temperature as the wool with no soap, let it stand a moment, then remove it and squeeze out the water. Repeat this plain water bath until all excess dye is removed and the water remains clear.
  9. Hang the wool or place it on a clear screen to dry.

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