The sixth 節気 “sekki” division of the traditional Japanese calendar is:
‘grain rain’ (solar term)
The first “kō” microseason within this division is:
(あし はじめて しょうず)
“ashi hajimete shōzu”
First reeds sprout
That makes 葭始生 the sixteenth microseason of the year!
It typically lasts 20~24 April.
Image credit: Road-Station.com.