flower calendar; floral calendar
A calendar that indicates the blooming periods of various flowers throughout the year. Often used in traditional Japanese contexts or gardening.
花暦を見ると、今月は桜の季節だとわかる。
Looking at the flower calendar, I can see that this month is cherry blossom season.
Compound of 花 (flower) and 暦 (calendar). The exact historical origin is uncertain, but it likely emerged as a descriptive term for calendars marking seasonal blooms.