quotes the Gemoro in Bava Metzia 103b.
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
ולקחתם לכם ביום הראשון- Rishon L'cheshbon
Avonos. “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(shaking of the Lulav)
rids the world,from harmful winds and dew. TheTorah said
the Lulav should be taken on the first day of זרע
the planting season.