Why won’t my Romanesco broccoli form a head?

Broccoli ‘Romanesco’ is really a green cauliflower. Like cauliflower, it is very sensitive to an inconsistent growing environment (fluctuations in weather, temperature and water). Gardeners in regions that have very even growing conditions can grow this variety best, as do greenhouse or hoop-house growers. This is also a very long season plant and it does not form heads until late in the season. It may not be mature enough yet.