A medium yellow dye can be obtained with St. John's Wort, using the tops and an alum mordant. For bright yellow, use plant tops and a chrome mordant. Though this is a hardy perennial, don't be surprised if it is short-lived. It spreads by runners, but can be controlled by pulling. This plant likes full sun, yet will tolerate some shade with fewer flowers.
Harvest leaves in the morning, when the oil content is highest.
Dry and store in a dark place. Magickally, St. John's Wort is used for protection. Burn it in the hearth or bonfire. It is traditionally gathered at Midsummer, and can be also effectively used as an amulet of protection. Its planet is the Sun and its element is Fire.