Usage patterns
〈場所〉に葦が茂るreeds grow thick in a place
Reeds are growing thickly along the riverbank.
葦を刈るto cut/harvest reeds
In autumn, work to cut the reeds along the river takes place.
葦の茎で〈物〉を作るto make something from reed stalks
I made a flute out of reed stalks.