This is the seedling I threaded through a hole in a stainless steel disk.
and here's the meatal plate. The original roots have long ago died off. New roots growing over the disk provide horizontal nebari but not perfect.
Always in containers. These are in the 5 year pine competition so not really time to do ground grow and still get to a pot at the end of 5 years. Also aiming for smaller trees so slower container growing helps reduce large cuts and other problems that can come from ground grow.
I also grow some in the grow beds each year. They are for larger trees where a few faults are less noticeable. Ground or container depends on what you want, what compromises you will accept and how long you want to spend on development.