Peppers like heat-more heat then even tomatoes. When transplanting anything outside, we must consider both air temperature and soil temperature. Our soil temperature right now is not warm enough yet to plant our pepper transplants out in the garden even though the air temperature is warmer now. Tomatoes went outside in the garden for me last week inside wall of waters but my peppers are still inside the house under lights waiting. Waiting, waiting, waiting. The soil temperature is in the 60’s which is still too cool to transplant peppers.
If you plant peppers while the soil is still too cool, they tend to stall out meaning they stop growing altogether and don’t restart growing even when the soil gets warmer. You’ll have to re-buy them. Trust me, I know from experience. I’ve even tried growing them in wall of waters (WOWs) and the air temp stays warmer inside the WOW but the soil temp can still be cool. Peppers would love the soil temp to be 70°F when transplanting outside. So it is best to wait. How long? I plant all peppers the first week of June when I know the soil temp is much warmer.