Depends on where you live and your climate zone. I'm in zone 6, and lettuce and spinach can be out now (once they've been hardened off). Beans generally can't go out to the frost free date (which varies per your zone, but for where I live is around May 15th.). It's been a cool spring here, but it may actually be getting late for the spinach (again it depends on your zone). I'm not familiar with arugula or fennel, so I can't comment on those.

All of these are cool weather plants except the beans; therefore the only thing that is important is that you are past the last frost date. In VA (Zone 7, almost 6) it is about April 20.

Im in Zone 7a I have been hardening

Here are my seedlings