The heads don't get really large. But that might be a benefit since really
large leaves are often less tender, IMHO.
One nice thing to know is that you can harvest leaves as you need them.
There is never a need to yank an entire head of lettuce. This way you can
get many more lettuce leaves from a single head over time.
As you can see, the head near the top left has quite a stalk on the bottom
where many leaves have already been harvested.