Hi,
Poor head development can be the reslut of either using transplants that have been stressed in some way in the growing process such as poor watering, poor vertlity and the plants tend to be stunted and not vigorous when set out in the garden or the plants are set out and again not established well so they take off growing and then if warm/hot weather ararives they tend to bolt (flower) and not set good heads. I might suggest thinking about growing some late fall brocolli by starting plants now and setting them into the garden when we normally gets some cool fall weather which they like.
