Chinese cabbage is either bok choy or choy sum. Choy sum is the flowering chinese cabbage.Neither has a heart like an English cabbage. They are long loose leaves but the choy sum also has edible flowers. Use in stir fries or the very young leaves can be eaten raw in salad.

Welcome, Jerzegirl!

Scotsgran, wong bok (aka Napa cabbage) is the plant most often called Chinese cabbage, here in the States, and it forms an elongated head.

Jerzegirl, in most parts in the country, it is best planted in late summer to form heads in the fall. The lengthening days and warming temperatures of spring and early summer tend to make it flower (called bolting), and that usually ends the life of the plant. I'd suggest you try again in August with starts, or late July with seeds. That's assuming you don't live in a climate as hot as mine!

Chinese cabbages and pak choy are prone to bolting. Sow some more.