Lettuce likes it cool
Lettuce is a spring crop, and produces more and tastes better when grown in cooler temperatures. During the summer, keeping lettuce in a cooler spot in your home will produce better results. And lettuce loves cold feet! Some AeroGardeners put a few ice cubes in the reservoir once or twice a day to cool the water down a few degrees. This is especially good for your plants if the AeroGarden's ambient room temperature is in the low 70s (that's warm for lettuce!).