I've never planted ornamental kale before, but since purchasing, I've read that its best to buy later in the season and avoid root bound plants as they never achieve their true color. ..which I did.

Can I plant them in deep containers or in the garden with the lower leaves at soil level ? Or plant the same depth as the four pack and cut them back and hope for new sprouts?

The plants were very inexpensive but I would rather try a "kale beginners experiment" than just throw them in the compost.

From what I have read most ornamental kale doesnt get its real color unless its quite cool, best even after a frost or two.

I dont think planting it deep is a good idea. generally only viney plants can be planted deeper.

Cutting it back some will probably make it divide, but with the form of the type you have I dont think that it would look right.

If there is a longish stalk with no leaves, it is probably because the grower, or seller cut off dead leaves from the bottom, it surprises me that at 12" it is not root bound. Its obviously been around for a while.

I would just plant them as is and see what happens.