Installing 30amp breaker
Generally only 30A receptacles are allowed on 30A circuits, and 15 or 20A on 20A circuits, and 15A on 15A circuits. 

210.23(B) Says a 30A branch circuit is permitted to supply fixed lighting units with heavy duty lamp holders in other than dwelling units...

So if the building occupancy in County records is residential you likely wouldn't be allowed to do that.

Alternately you install a $20 6 space electrical panel in the grow room and break your lighting circuits down to easier to handle 15A or 20A circuits and wire.

If in an allowed occupancy you are allowed to use cord and receptacle connections, but there are additional requirements in Article 422, including the receptacle is required to be directly above the light and stain relief issues.