Why use au printemps and not en printemps?

In French, "au printemps" is used instead of "en printemps" because "printemps" (spring) is a season that is considered a specific period of time, and the preposition "au" is used with seasons. The preposition "en" is typically used with months and years, while "au" is appropriate for seasons like "printemps," "été" (summer), "automne" (autumn), and "hiver" (winter). Thus, the correct phrase is "au printemps" to indicate the season of spring.