Hi, the last couple of times we planted broccoli the heads spreaded and flowered instead of staying the shape you normally see.
What can be done to make them grow properly?
you have to pick them when the head is still in bud, no matter how big it has got. Broccoli are big feeders so need good fertile soil, and do better planted in late summer/ autumn to grow over winter/spring . that way you miss most of the white butterflies and hot weather that can make them bolt early.