This is red lettuce and the four lettuce plants at the bottom have all been harvested. The one to the far left (left bottom corner) is just a stump, it was picked yesterday. The one next it, to the right, was picked 3 days ago. You can see new lettuce leaves forming. The two in the far bottom right corner were pick 7 and 10 days ago. They practically have new heads on them.
The lettuce in the middle of my raised bed has not been picked and has been growing for about 40 -45 days. Behind the lettuce is swiss chard.
Lettuces will grow new leaves if you leave the roots in the ground. This is a great way to keep the lettuce coming to your table.