More broccoli trouble...

I would guess its ad a bit of a chill,been dropping quite low the last couple of nights 

In fact, there are two different groups of Broccoli plants which are:-

Sprouting Broccoli or Brassica oleracea Cymosa group.

This type of Broccoli is sown in the Spring and usually eventually harvested in late Winter and early Spring. In other words, it is a group of hardy, over-wintering varieties of Broccoli to eat in late Winter and Spring. But just to complicate matters, there are now sprouting broccoli cultivars that are ready for eating in the Autumn.

Calabrese or Italian Sprouting Broccoli, or Brassica oleracea Italica group.

This type of Broccoli is sown in the Spring  and harvested in the Autumn and early Winter, as it is not frost hardy. Some catalogues also list the Romanesco varieties (look rather like green cauliflowers), in this group. The edible spears are usually shades of green.