Hi Graham,
“You hear” is likely to be a homophone indicator. Because it’s at the end of the clue we can conclude that grasses is the definition and the solution sounds like a word for grow.
Here, the answer is a specific type of grass.
Thank you Jono. It’s strange how one can let the brain work on it overnight and get it the next day! Having a wrong second letter didn’t help, but all sorted now.