The Six Seasons

Rashi on Zera V'katzir ,Kayitz Vochoref -- quotes the Gemoro in Bava Metzia:

There are six seasons in the year, each lasting for two months.

The first season of Zera starts in Chatzi (15) Tishrei.

My father a"h said, on the famous Midrash of
Ulekachtem Lochem Bayom Harishon -Rishon L'cheshbon Avonos

that perhaps the orignal girsa was, Onos (seasons) instead of Avonos
(difference in spelling only one vav)

The first day of Sukkos (15 Tishrei ) is the first day of the first season Zera.

The Gemoro says that the Na'anuim rids the harmful winds and dew.

Therefore the Torah said the Lulav should be taken on the first day of the
planting season.