I think for me, here, April 15 or so. Lettuce transplants grow quick, so two or three weeks, they should be ready, right? That would be before it gets hot. This year has been weird, so they might have even made something if put in on May 15.

I love me my greens so start by seed and transplant every 3 weeks or so all the way thru early November. I've slow bolt varieties that I'll put out in the hot months, in an area that gets morning sun, afternoon shade and will need a good amount of watering.. But so worth it. Black cabbage and Russian kale also seem to handle the heat well .... They won't do as well as cool weather season but not bad.....