Having trouble with indoor container grown lettuce
I'm currently growing arugula, spinach, and lettuce in 1-gallon containers under fluorescent lamps in the garage.
The arugula is doing great. The spinach is doing so-so. The lettuce, however, is not doing so well. I was getting a good weekly harvest for the first month and then last week they all started to exhibit wilting near the tip of the leaves. As each day has passed, more area of the leaf exhibits wilting. It looks like a plant that is thirsty, but the soil is moist both to the touch and also according to my moisture meter.
Any ideas what is going on? For reference, I'm growing red velvet and buttercrunch. Temperature in the garage is ~60 F. The top of the plants are ~4-6 inches from the fluorescent lamps and get exactly 12 hours of light each day.