This beautiful wildflower creates an incredibly bright and wash-fast yellow.
It is very easy to dye with these beautiful flowers and they yield a gorgeous green when overdyed with indigo...

but that's a whole other story... to follow in another instructable!

A few notes before you go further...
As a rule of thumb, use a 1:1 ratio of fresh flowers to weight of fiber (i.e.: 100g of flowers to 100g of wool )
You can always use more or less, it will simply affect the intensity/shade of color. I suggest you experiment and explore with various quantities to figure out what you like the best!

Alum is generally used at about a 15% concentration. (i.e.: 15g of Alum to every 100g of wool)

Step 1: Materials and Equipment

Tools and equipments

Stainless steel pot (or unchiped enamel pot) NO aluminium as this may affect the color.
Dishwashing gloves (it's good if they are thick as the water will be hot)
Wooden stick/spoon (or anything you can stir with)
Strainer. It can be cheese cloth, a paint mesh (this is what I use), etc.
Plastic or glass container to strain dye liquid

OPTIONAL
PH test strips (To test the water PH )

Materials

Goldenrod flowers
Pre-mordanted wool yarn ( check How to Mordant protein fibers )

Step 2: Extracting the Dye

I find a 1:1 ratio of Goldenrog flowers to water works well.

(If you found PH strips, now is a good time to test the water!)

Put Goldenrod Flowers into you stainless steel pot.
Pour enough water to generously cover the flower
Turn on your stove to medium and bring to a gentle simmer, making sure it doesn't boil.
If it starts to be very low on water (too much water evaporated), just add a little bit of water.
After 1 hour, turn off the stove and let cool down for a while.
Strain the dye liquid usig your mesh/net. Squeeze as much as you can to get all the precious dye liquor...

You are now ready for a wonderful dye bath !

Step 3: Dyeing ( Finally! )

You will have a dark amber liquid... this is your lovely yellow in perspective!

You will find out that the color evolves very much the dyeing process...
At first, the color is very light brown, and after a little while of sitting in the dye pot, you'll get an amazing yellow!
Your yarn needs to be wet, so make sure you let it soak in water for minimum of 1 hour prior to dyeing.
Pour the dye liquid in the dye pot. With your gloves on, put your yarn in the dye pot. Add enough lukewarm water to cover the yarn and so it can move freely. Gently squeeze the yarn to fully soak it with dye liquid.
Turn on the heat to medium, bring to a gentle simmer and hold this for about 1 hour, stirring every once in a while to assure even coloration of the yarn. (Go gently while stirring, as heat + agitation = felting)
Let the whole thing cool down before taking out the yarns. If you are patient enough, I recommend leaving the yarn in the dye pot overnight.
Without any rinsing, let the skeins air-dry out of direct sunlight. This help better color fixation.