AllenF, is right. Biennial or not my cole crops bolt as soon as it warms up. I plant collards, broccoli, brussel sprouts, cauliflower, turnips (several varieties), mustard (several varieties), rape and kale every fall as I love winter greens and try to have aomething in the garden year round. When it bolts and goes to bloom I let the bees have it as long as they want it and then hit it with the mower and turn it in when I break ground for spring.
I figure I'm getting a triple whammy. Pollen when the bees really need it plus whatever nectar is there, added organic matter for the soil and mustard turned in has anti nematode properties.