It is very doubtful that any lettuce planted now would do anything in terms of producing an edible harvest. Lettuce is a cool-season crop that does best when it is grown when temperatures are above 20 degrees and below 80 degrees.

Heat-tolerant varieties are heat-tolerant in areas where summertime highs only hit the mid- to upper-80s and where 90 degrees is considered an intensely awful heat wave, but are not tolerant of the kind of heat we have here. Shade helps them when we are in the 80s but once we're in the 90s, shade doesn't help enough because it is hot air and soil temps that hurts them and shade only slightly lowers the temps. I have used shade cloth to shade my lettuce this spring on any day that our high temps exceed 85 degrees and some of the varieties are going to seed anyway.

I planted lettuce in earliest February and have been harvesting for about 6 weeks or so. Some of my so-called heat-tolerant varieties are now going to seed, likely becuase we've already had several days here in the 90s Usually they make it until at least mid- to late-May.

The OSU-recommended planting dates for lettuce are February 15th thru March 10th for spring gardens and August 1st thru 15th for leaf lettuce for fall gardens. In my part of the state (southcentral OK) it is too hot Aug. 1-15, so I plant around September 1st, which often still is too hot, but I can't wait any later because I want it to be a good size before the really intense cold arrives.