While St. John's Wort has a long and fascinating history related to magic, fairies, and rituals, it remains today a very useful dye and medicinal plant. Yellow and red dyes are obtained from the flowering tops and stems of St. John's Wort, depending on the mordant used. Harvest the leaves in the morning, dry them and store in a dark place. The fresh leaves may also be pressed for their oil, then added to olive or other vegetable oils which will turn red with age, and keep for about 2 years. It can cause photosensitivity, dermatitis and other toxic reactions, although problems rarely result from normal dosage.
Gardeners often complain of a rash caused by working with the plants.
Gloves should be worn initially until sensitivity is established. It is rumored to have been used by St. John during the crusades to clean the wounds of his troops. It has been known to cause photosensitivity in organisms that ingest it, especially grazing sheep in Australia and cattle in the United Kingdom. So much so that the animals who grazed on it died from sun exposure. No deaths due to sun exposure, have ever been reported from human usage of the herb, but in-depth controlled studies are just beginning.