I had the same question. This is also my first year growing Asian vegetables. Purchased the seeds from EvergreenSeeds and transplanted them outdoors two weeks ago. Mine is still small. I'm guessing I will do as you did Broccoli, cutting the stems when they're thick as pencil (like those sold in the supermarket). These are supposed to be cut and come again.

Confirmed. My Gai Lan (gai long?) did send out side shoots after the main trunk was harvested. Some of the sides grew from the bottom of the main trunk, some from spreading root.

do you not need to cover yours with some kind of fine netting or fleece? kaillan (as it's says on my seed packet) is from the cabbage family and these would get attacked by the dreaded cabbage white butterfly when they would lay thousands of bright yellow eggs on the underside of the leaves. i'm growing kaillan too for the 1st time this yr in the UK and they're about 6" spread in diameter. they've grown well but the stem is taking awhile to thicken tho'.