I'm growing Romanesco cauliflower for the first time this year. The plants are doing really well (touch wood!) and are starting to form lovely little green spiky cauliflowers. How big can I safely let them get before harvesting them? If I wait too long will anything happen to them? The reason I ask is that all the plants look like they are growing at the same rate and I may end up with a lot of them being ready all at once.