You can see here how the stems of the Cavolo Nero have become elongated as the tips begin to form flowers.
The lower part of the stem is bare where the leaves have been picked from the bottum upwards:
Taking the plants indoors, I cut off and discarded the lower stems, but kept the bushy "crowns" intact.
That's a decent amount of greens! Because we were not going to be able to use the crowns immediately, I washed them and packed them into large "Stayfresh Longer" bags. I find these bags very useful indeed. They keep fruit and veg fresh for ages. The Cavolo Nero would probably last 3 weeks if I wanted it to.