Did you ever stop to think about what you're actually eating when you have broccoli for supper? All those little green things are actually flower buds. If you are raising broccoli in your garden and you happen to wait too long to pick them, they will start to flower. (And by the way, that brown thing on the broccoli head shown above is a dried up basil leaf. We found that basil really does repel cabbage worms.)The flowers are actually quite pretty. Bees like them too.
The other night for supper we had some broccoli that was flowered out some. We ate it anyway. Broccoli flowers are actually quite good when raw, and would be a nice spicy addition to salads. Cooked they taste like--broccoli.
Once you cut off the main head of broccoli, even if it has flowered, just be patient. It will send up secondary shoots. They won't get as big, but they will taste just as good (or bad, depending on your opinion of broccoli.) I've had friends who have pulled out their broccoli plants once they start to flower. I also just read an article that said that once broccoli flowers there is nothing you can do, but that's a shame because you can keep harvesting broccoli for a long, long time in warm or cool weather.