Thats a lot of power to be switching, I'd recommend first making sure you have a properly sized circuit to handle that kind of load, and properly sized wire corresponding to the breaker. Thats 30 amps, at 240v assuming 100% efficiency, and all 12 on at the same time. Don't even think about running this all on 120v. Minimum wire size, depending on type and length of run will most likely be #8, although in most cases you'll end up having to use #6. Yes, 10 wire is rated for 30a but running conductors/equipment at 100% rated capacities is never a good idea, and will get you code violations, heat, shorter equipment life, and fires more often than not.
The easiest, cheapest way to get set up for those would be to get a correctly sized circuit into your grow area, and hook it up to a heavy duty contactor(at least 40a rated), and use the lighting controller/timer to trigger the 120v coil. On the load side, run the wires to a box with 12 outlets for your ballasts to plug into. You can pull 120v from one of the 240 legs for this, which I would highly recommend so you can avoid having high potentials in close proximity to each other on different circuits. Those kind of shorts/faults can get real ugly in a hurry.