Cauliflower

  My cauliflower plants were doing very nicely last week, small but tight heads. This week they are all looking as if they are "shooting". The florets are all growing long stems and of course the plants do not look good. I had turned some leaves over the heads to protect them from the sun. Can someone tell me what has gone wrong.

the best caulis we grow have been snow ball , out of 20 we only had 2 that bolted , thats great , usually as soon as we see the curds we pull them , freezers ful now , yippee