Ertha rules fertility, the hearth, the home, domestic life, and the Wild Hunt. She is the matron of witches and peace envoys. The many names by which she was known in northern Europe include Erda, Eartha, Hertha, Herta, Hretha, Hrethra, Bertha, Nerthus, and Rheda or Rhede. Erthaís titles include Mother Earth, and Peace Bringer.

Evergreens, especially fir boughs, are sacred to Ertha. She is hostile to iron. Hrethmonath, the month of March, is sacred to her. Ertha is celebrated at Winter Solstice, Spring Equinox, and on May 1. At Winter Solstice yeast cakes called Erthaís slippersí were once baked. The goddess was said to have visited houses on the night of the Solstice, by descending through the smoke in chimneys, and filled the slippers with small gifts for the members of each household.

Invoke Ertha by any of her names for peace, prosperity, hospitality, fertility, abundance, grounding, witchcraft, magic, diplomacy, earth magic, peace missions, household matters, hearth magic, kitchen witchcraft, and for divination, especially when fir boughs are burned. Sacred groves and altars built of flat stones are appropriate places for Erthaís worship or invocation. The smoke from burning fir boughs is traditionally used to invite her presence, and her assistance with divination.