Today’s post is a difficult one because of the theme. It is about Festivals, Days, and Times sacred to Haides. Because of his role as Lord of the Underworld there are no major festivals that would be in his honor.
Haides does seem to have had some role in the Eleusinian Mysteries because of evidence of an altar to him at Eleusis. He also had altars in other places like the Temple dedicated to the Erinyes in Athens, but it is unclear based on ancient writing if there was any special cultus paid to him there.
The main rituals that involved Haides were funerary rites. This is likely to be due to the fact that those rites were intended to honor the deceased person’s passage into the Underworld. He would also likely honored during the Genesios Festival, as that was the annual festival to honor the dead — similar to Memorial Day in the United States. If you celebrate the secular holiday of Halloween, this is a time when it might also be appropriate to honor Haides as this holiday is close in the calendar to the Celtic holiday of Samhain — a festival that many Wiccans and other pagans dedicate to honoring their dead and the Gods associated with them.
He would also have been honored in necromantic rites. These were primarily at his one oracle in Thesprotia during the classical period, but in the modern era we do not have any established method of necromancy which is well researched. Because of this, I would suggest only doing divination about what your Honored Dead would want of you on the Genesios or on days such as the anniversary of their passing or their birthdays.