godan verb (-su), transitive verb
Transitive: to grow something on one's body (hair, beard, mustache) or to cultivate plants intentionally.
彼はひげを生やしている。
He is growing a beard.
庭に芝生を生やしたい。
I want to grow a lawn in the garden.
godan verb (-su), transitive verb
let grow; allow to grow
To let something grow, often with a nuance of neglect or lack of maintenance, such as weeds or unwanted hair.
空き地に雑草を生やしっぱなしにしている。
They are letting weeds grow unchecked on the vacant lot.