On my drive to Sion Hill I drive past thousands of dandelions on Lansdown Road. One day, I pulled over and picked a good clump to see if they could dye wool the same sunny yellow that the flowers produce.
Using the same extraction method as for dried plants- I soaked the flowers and stalks for a few hours in cold water before heating for an hour and leaving to cool. Then I strained the liquid and added the alum mordanted yarn (at a ratio of one part yarn and three parts dye stuff) and heated for an hour, leaving to cool overnight.
The resulting yarn colour was a buttery yellow - not as vivid as I was hoping, but not a bad colour considering the materials were free and in abundance!