According to Rebecca Burgess’ Harvesting Color, page 162:
If havesting fresh madder, the root must be three years old to produce strong reds.
Madder [Rubia tictorum], or Common Madder, is a member of the Madder (Rubiaceae) family. The live plants in the photos are being grown on our back porch. Alum is used a mordant with yarn to fix the dye.