This is the first season that I've had a crop of hypericum perforatum (St John's wort) to use in a dye bath. It's a small variety characterised by what look like pin pricks in the leaf (actually tiny pockets of oil - they show up as little black dots in the second image). In high Summer the flowers have been a treat to use as a dye. At the weekend I set up a solar bath on the back wall and within a couple of hours the alum mordanted fabric was turning green, the unmordanted a soft pink.
As with all dye plants, timing is everything. I repeated my experiments today with freshly picked flowers that looked a bit past their best. The result was a uniform dull yellow. Time to think about next year's growth, although the remaining flowers are steeping in olive oil, to use as a salve for sore skin this winter.