It’s always a bit nerve-wracking growing cauliflower as it can seem that for ages the plants just grow more and more leaves, and that the cauliflowers themselves aren’t forming.
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 to 4 months after planting out. So if you only planted it in July, then you probably won’t see a head forming for another few weeks. However, if you planted them back in May, then you should hopefully have seen a head forming by now.
If you planted in April/May, and think it should have formed a heart by now but you’re not seeing anything, it is likely that the plant suffered during a long dry spell and got too hot, or perhaps that the soil is a little loose for them. You could still leave them in the ground for a little longer, just in case, but it might be good to start accepting that they may not form a head at all. Sometimes the plants will produce lots of small florets instead of one tight head. Again, this is likely to be due to hot, dry conditions. You may find it helps to mulch cauliflowers next year to keep moisture in the soil, and water more frequently to keep the soil cool. They also need a lot of organic matter, so dig in some compost before planting.
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 from the weather. Once you’ve done that you should be expecting to harvest the cauliflower around 2 weeks later. Try to harvest before the heads start to open up.