There are two ways to harvest lettuce in salad trays. You can pick a few outer leaves from each plant for a salad, or you can do cut-and-come-again lettuce culture, where you cut each plant off 1 1/2" (4cm) above the ground. Keep watering and the lettuces will regenerate for a second cutting a couple weeks later. I usually pick individual leaves as the lettuces are growing, but once they reach full size, I harvest the tray entirely. You can usually get 1 additional cutting, but after that the lettuce gets bitter, so I take it out and run the stumps through the worm bin. Photo by Steve Masley.