Jāņi was originally a pagan custom; after Christianization it became nominally associated with Saint John the Baptist's feast day, which falls on June 24; therefore the festival begins Jāņu vakars in the evening of 23 June and all through the night, where people Līgo (sway) into the following day, not on 21 June/22 June when the summer solstice actually takes place.
Jāņi is thought to be the time when the forces of nature are at their most powerful, and the boundaries between the physical and spiritual worlds are thinnest. In the past, evil witches were believed to be riding around, so people decorated their houses and lands with rowan branches and thorns in order to protect themselves from evil. In modern days other traditional decorations are more popular, including birch or sometimes oak branches and flowers as well as leaves, especially ferns. People wear wreaths made from flowers for females, or oak leaves for males; in rural areas livestock is also decorated.
Jāņi also is thought to be the perfect time to gather herbs, because it is believed that they then have magical powers. Other practices of magic in Jāņi vary from fortune-telling to ensuring productivity of crops, as well as livestock fertility. A well-known part of this celebration is searching for the mythical fern flower, though some suggest that the fern flower is a symbol of secret knowledge; today it is almost always synonymous with having sexual relationships. Despite common belief, no remarkable increase in birthrates is observed nine months later .
Another important detail is fire: A festival fire must be kept from sunset till sunrise, and various kinds of flaming light sources are used; usually these are bonfires, which traditionally people jump over to ensure prosperity and fertility. Traditional food during Jāņi is a special type of cheese with caraway seeds, made out of curd, and the traditional drink is beer. Many people make the cheese of Jāņi themselves; a few also make their own beer.
Representatives of Latvian Emergency services often warn that Jāņi can be harmful to health because of the amounts of food and alcoholic beverages consumed, as well as maltreated fires.