My cabbage plants are beautiful but won't head up. Why?
Certified GKH Gardening Expert
It may be that it is too warm or that you just need to give them some more time. There are a few pests that can cause this too. This article has more information on them:http://www.extension.umn.edu/gardeninfo/diagnostics/vegetable/cabbage/headnone.html
If you suspect that it may be heat, mulching well around the base of the plant can help.