Hi -
I've tried both! I think the trick to fall seed sowing is to do it early enough so the plants get established. Mine didn't last year, but they did come up! I planted plugs as well about a month ago. The fall seeded plants are about ready to bloom, so that's a plus.
Try both!
Wendy

I would put my money on Fall planting for earlier bloom. But, as you know, gardening is like a Roulette game, sometimes.

The best larkspur I ever have are the ones that self sow. They are always larger and earlier than the ones I sow in the spring. I am in zone 5 and they reliably reappear every year so I don't think you will have problems in zone 7.

That said, when I have tried to fall sow I have had mixed results. Maybe I sowed them too late?
Kirk