Whatever you're planting in is so dry at the edges that it's bowing away from the plastic. The physiological leaf curl is caused by environmental stress, but that could be too much water or too little. If this has just happened, I would say you're not watering them enough.
I realize that most of the folks here harbor terrible fears of over watering, fears the burble up from the depths like Cthulhu rising, fears that wake them screaming, "Too Much Water!" into the dark; but honestly, if your pots have good drainage, it's difficult to over water.