Growing cauliflowers will have been challenging for anyone in the UK this summer as they really thrive in cool, consistent conditions. If yours haven’t formed a head yet, then try to think back to when you planted it out. You would normally expect to see the head about 3 months after planting out. So if you only planted it in July, then it should start to form a head around now and you might be lucky. If you planted them back in May or June, then you should really have seen a head forming by now. If not, it is likely that they suffered with the hot weather this summer. It’s most likely that they won’t recover but you could still leave them in the ground for a little longer, just in case!
If you can see a small head forming, then things are looking good. Once it reaches about 5-8cm in diameter you can tie the outer leaves around the head using an elastic band or twine to hold it in place. This helps to keep the nice white colour rather than seeing the cauliflowers turn a bit yellow. Once you’ve done that you should be expecting to harvest it around 2 weeks later.