Q.What should I do to produce broccoli heads?
I have broccoli, Romanesco variety, planted since early June from seed. It has not produced any heads. What should I do to produce the heads? I have 5 plants from very large to small.
4 plants share a raised bed (Kingsize waterbed frame) with other cole crops, reg. broccoli, turnips. I know I need to fertilize. Is Miracle Gro ok? Would compost or mulch help? I found with regular broccoli adding manure seems to harshen the taste, but I do add manure and peat to beds each spring.

Most cole plants perform better in cool weather. If you are growing from seed, consider having the plants ready to get into the bed 8-10 weeks before last average frost date for your zone for a spring crop. For a fall crop, try to plant 8-12 weeks before first average frost date. It seems that Romanesque is unreliable in forming heads at times. The reason has yet to be discovered. Since this plant is more closely related to cauliflower than broccoli, I suggest adding some lime, either at transplant, or as a side dressing.
Hopefully, this article will help:
https://www.gardeningknowhow.com/edible/vegetables/broccoli/growing-romanesco-broccoli.htm