Answer: The problem could be in the type of Broccoli raab you have. In general, there are two types, namely: "Broccoli raab Fall" and "Broccoli raab Spring." They are essentially the same except that the fall strains tend to form flower heads a little earlier than the spring varieties. There is generally very little difference between the two. Some of the fall strains will overwinter better than the spring varieties.
If planted early in the fall or late in the spring, this crop requires about 60 to 65 days from seeding to first harvest of the flower heads. If planted in the late fall, harvest is usually delayed until late winter or early spring. Your planting date was a bit late, although your deep south location may warrant such late planting. Most southern gardeners start seeds in August to September.
It may also be that you have collard plants rather than broccoli rabe. If you have grown these before, you may notice a difference in leaf shape and color tint, in addition to leaf size.
I can't think of anything else that would cause the plants to not flower. They have been in long enough to do so. This may be one of those "garden mysteries" that remains unsolved.
Good luck with your plants and I hope they decide to flower soon!
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