What is the collective noun of hedge?

There isn't a specific, commonly used collective noun for a group of hedges.

However, you could use descriptive phrases like:

* A row of hedges

* A line of hedges

* A screen of hedges

* A barrier of hedges

* A thicket of hedges (if they are dense and interwoven)

The best choice would depend on the specific situation and the desired effect.