You would need some pretty darn big containers to grow either laurel to 8'!! The largest laurels we sell at my nursery are about 6' and those are B&B, not container grown. Growing anything in a container is a natural dwarfing process - because the root development is restricted by the container, the top growth is restricted as well. You can continue to upsize the container (and will need to frequently if not root pruning) but that's a great deal of effort, lots of the potting soil needed and still some BIG pots to expect that size plant any time soon. Then there is the soil interface issue when the time comes to plant in the ground and the difficulty in actually managing and planting 8' tall shrubs.The rootball will be big and very heavy.

You would be better off planting directly in the ground, providing you follow the suggested recommendations for planting in a clay soil.

Are there any rough numbers on how wide and deep the rootball would be relative to the height and width of the visible part of the plant? I understand your points and I can plan around those facts. Maybe I transplant at a much smaller size, or maybe I plant directly to clay. But having a general rule to that lets me calculate the size of the rootball from the size of the plant would be really helpful to the planning process.

What are the recommendations for planting in clay?

Okay, so the basic idea is to get the planting above the perched water table of drenched clay soil and maximize whatever drainage you can get out of such a poor draining soil?

Don't back-fill with any soil that is significantly more coarse textured than the existing soil. Otherwise the planting hole may become a collection point for water.

Planting high is just a way to keep the entire root crown from being immediately immersed into a high water table situation. As time goes on the specimen will still have to be able to grow in the existing circumstances, if it is a kind that reaches any size at all.

Tree and shrub root systems often become much larger than their tops over time. For instance a 330 year old oak tree in my region was determined to have a root spread about twice the average crown spread.

repotting plants beyond a foot or two tall could become a real big problem ... how exactly would you lift a 7 foot tree out of the old pot ... position it in a new pot.. and make sure it stands up in the new pot ... etc ....

for that reason alone.. they need to go into the ground... imo ...

ken