First time growing cauliflower problem

[Veggrower123]

I've been trying to grow cauliflower got my first head now it looks like it rotting. Do i cover it when it rains.

[cariann88]

The leaves should be covering the head of the cauliflower to stop it from discolouring

[Greenleaves]

What variety is it, a winter hardy one I presume?

The plant looks quite small for most winter hardy types so perhaps frost damage. What Carrie says is correct but mainly in the summer months when we have strong sunlight