Hello Eileen,
It was Tall Green Utah and I had cut the main stalk, leaving sideshoots growing out of its base which made smaller mini-hearts after about four weeks. The second harvest was worthwhile, but quite sluggy it must be said. Picking individual stalks is worth trying, I have not done that.
There is a variety called Leaf Celery but it is a little more stringy and strong-flavoured, good for soups and stews and it can overwinter in a polytunnel if frost is not too severe, sow in early September.