Can you imagine trick or treating among the flowers in May? That’s when Halloween used to be.
It used to be the late May/early June evening before All Saints Day. (Hallow meant holy and een was short for eve or evening.) Then it was shifted to October and went from a gentle day of prayer to a scary evening of witches, bonfires and spooky fun. Why? What is so scary about October?
Halloween, the evening before All Saint’s Day was moved from spring to fall and became much scarier! Source: Wikipedia
The early Christian church used to shift many of its holidays to fit the schedules of its converts. If people were used to partying at certain times of the year, the Church placed a Christian holiday at that time. Christmas was moved to Winter Solstice and replaced the cheerfully debauched Roman Saturnalia. (Fortunately, gift giving survived the change.) In 835, Louis the Pious switched All Saints Day to November 1, to replace pagan harvest festivals.
All Saint’s Day was moved to the time that most Western Europeans slaughtered their animals! A rather bloody time of the year! Source: Wikipedia
Moving the holiday from warm spring like weather to chilly autumn, however, changed the whole nature of the celebration. All around, the weather was growing colder and plants were dying. As the grasses died, people had to decide which livestock they would feed all winter and which would be slaughtered. (The colder weather meant the meat would last better than it would in the heat of summer.) It was a cold, bloody time of the year. To the Celts, it was Samhain, summer’s end, a time of growing darkness when fairies and the dead could move abroad.
Brrrr! A holiday amid spirits and slaughtering feels very different from the spring like days of flowers and little lambs.
Europeans countered the colder, darker times with feasts and treats, bonfires and sometimes (to deceive witches and spirits) costumes. They frequently appeased the dead by visiting and cleaning the cemeteries. Some of these practices continued into the Christian era: Day of the Dead, Guy Fawkes Day bonfires, Halloween costumes and oodles of fattening treats.
Boo! Source: Wikipedia
So no matter what your faith, enjoy this Halloween. It is a time when people defy the growing cold and darkness with food and fun!
Evelyn Browning Garriss, historical climatologist, is a longtime writer for The Old Farmer's Almanac. She is also editor of The Browning World Climate Bulletin  and has advised farmers, businesses, and investors worldwide on upcoming climate events and their economic and social impact for the past 21 years.