Brassicas

Hello.  I have been an allotment holder for well over 55 years but since converting to organic gardening I have had a problem with Brassicas. I fertilise my ground with home made compost and well rotted stable manure. I supplement this with Comfrey and potash, and I always make sure that the ground is fairly well compacted. But with the exception of Brussell sprouts, Cauliflowers, Brocolli of all types and cabbages they all only produce small heads which are loose and not hearted up. What am I doing or not doing to produce first class crops to rival the professional growers? 

                                                                          Ted Lester, Shoeburyness, Essex.

Thanks everyone for the tips about improving my Brassicas, I shall stop feeding them with Comfrey. My Dad always used to top feed with a dressing of soda granules and had good results. I shall stop the Comfrey feeds and increase the watering.