[Welligog]

   I've tried growing caulis for the last 3 years and have gone from tiny dark brown buttons to huge dark brown dinner plate sized crowns.
So it seems I've cracked getting them to grow but havent solved the mystery of them being brown.
I've moved them around the plot and grown them in the polytunnel.  I've tested the soil and adjusted with lime, fed them with all purpose fertilisers, blood and bone, seaweed and high potash - still brown. 
Base soil is clay but I've added good quality top soil and compost over the last 3 years too.
Could any one offer any advice please?

[Aunt Sally]

Browning can be caused by:

A lack of Boron - give sea weed feed;

Too much sun  light - shade or tie outer leaves over the curd;

It doesn’t sound like aphid damage and fungal growth but do check that.

[jaydig]

I agree with Aunty about strong light discolouring the curds, so I always fold the leaves over as soon as I can see them developing.  I just snap the outer leaves towards the centre.  I grow mine under scaffold netting supported by hoops to keep out the butterflies, but last year when it was so hot for extended periods I also just threw another double layer of netting over the top to give shade and this worked. I removed the extra netting as things cooled down a bit. This year I've had really good, large, tasty caulis from Zaragoza, a variety I hadn't grown before, but I'll certainly do it again next year.