Dyeing Yellow-Green with St. John's Wort — The Midsummer Herb of European Dyers

Use 100-200% WOF of dried flowering tops. For 100 g of wool, weigh out 100-200 g of dried plant material. Harvest when at least half the flowers on each stem are open — typically late June to early July in temperate climates. Cut the top 20-30 cm of stems including flowers, buds, and upper leaves. Dry loosely bundled in shade for 1-2 weeks. Well-dried St. John's wort retains its yellow flowers and has a distinctive resinous, herbal scent.

Place the dried St. John's wort in a dye pot with 4-5 litres of room temperature water and soak overnight (8-12 hours). The water will turn a yellowish-green as the flavonoids dissolve. Unlike some plant dyes, St. John's wort benefits from a longer soak — the hypericin and other pigments release gradually from the flower heads and stems. By morning, the liquid should be a clear greenish-gold.

Bring the pot to a gentle simmer (75-80°C) and hold for 45 minutes. Do not boil — temperatures above 85°C degrade the hypericin and shift the colour toward muddy brown. Stir occasionally. The liquid will deepen to a rich golden-green. The flowers will lose their yellow colour and the leaves will darken as the pigment transfers to the water. A faint reddish tinge may appear at the water surface — this is hypericin, which contributes the olive undertone to the final colour.

Strain the dye liquor through a fine mesh strainer into a clean pot. Press the plant material to extract all remaining liquid. St. John's wort stems are woody and strain out cleanly, but the flower heads may be soft — strain thoroughly to remove all fragments. The strained liquor should be a warm, clear golden-green with a subtle olive undertone.

Pre-wet the alum-mordanted wool in lukewarm water for 15 minutes. Lower it into the St. John's wort dye bath at room temperature and slowly raise to 75-80°C. Hold for 45-60 minutes, turning the wool gently every 10 minutes. The wool will develop a warm yellow-green — a distinctive shade that is more green-tinted than pure flavonoid yellows like goldenrod or weld. This green undertone comes from the interplay between the yellow flavonoids and the red hypericin. The alum mordant produces the clearest, most vibrant version of this colour.

Turn off the heat and leave the wool in the dye bath overnight. The colour will deepen and the olive undertone will become more pronounced during cooling. Remove, squeeze gently, and rinse in lukewarm water until the runoff is clear. The final colour is a warm yellow-green to soft olive-gold — natural-looking and versatile. Lightfastness is moderate. The colour will gradually shift toward a warmer, more golden tone with light exposure over months. Dry in shade.