I have been growing Romanesco - that funny Italian cross between cauliflower and broccoli - for the first time this year. The heads have started to appear, but it has just occurred to me that I have no idea how to tell when they are ready for harvesting. I don't want to leave it too late, in case they go to seed, or something nasty like that. On the other hand, I want to give them as long as possible to bulk up.
Does anyone have any advice on the best time to pick?