As I see it, planting is no problem. So long as the things are properly hardened off - no worry.
Sowing is obviously a bit different. Yes, 40F is often quoted as the bottom line, and it's easy to take the soil's temperature. But, so often, one is persuaded by the Spring sun, and the condition of the seedbed, to get on with it. And, of course, covering the bed with a black fabric can soon warm it up.
But don't put all your eggs in one basket?? = Tim