My father used to grow cabbages and to help them heart up used to tie the outside leaves together to help, does it help?

Hi Pauline, this is very common when growing cauliflowers, to keep the heads white. Some horticulturalists used to do this many years ago with cabbage though, it was said to prevent the hearts splitting, however the seed and cultivars which are available now do not seem to have this problem. So, it may not be necessary, however it probably wouldn’t do any harm.