Why do cabbage heads crack? How can I prevent this?
This is usually due to rapid growth during warm weather on early cabbage, causing premature formation of a seed stalk when the head is maturing. Heads should be cut as soon as they are full grown. With the fall crop, there is less difficulty. Loosening the roots by bulling or bending over the head to break the fibers on one side of the stem delays cracking.
from 10,000 Garden Questions
