Cabbage not heading
I have been growing the cabbage for about 10+ weeks from seed. They have had a bit of a rough life. First they were slow to grow - temp was in the low 30's C. They were in the shade for about 4-5weeks. Then I planted them out. We then had heaps of rain - 4" the last day of March - 16" in March in total (QLD Australia time - sub tropical climate.) I gave them another hit of fertilizer then, 15N 4.5P 14K. Now they are just producing more and more leaves. An old round ball variety - both red and green. I had savoy cabbage like this last year. The sugar loaf produced big heads but the savoy just great big leaves. Bigger than a tennis racket. Temp now is 14-17 C at night and 24-27C during the day - coming into winter. Never had this problem in 30 years. I think my soil is just too rich at the moment.
Goodness, they have had a rough start!
This article will help you pinpoint the issue.