No, you don't need 10 in pots because the roots weren't positioned in the soil like you see now, but were much more spread out/horizontal.

Looks to be some kind of tap root?

eta: 5 gal. pails would do it. Drill drainage holes of course.

bengz, the ”tap root” is stiff and can’t be bent. Any thoughts on whether these are rooted cuttings or seedlings,

I would think seedlings that size would have much more of a root system.

Who told you they were from seed?

OTOH: would cuttings have a tap root?

Asimina is propagated through seed and named cultivars through grafting. Cuttings are almost impossible. What you see at the pictures above are typical seedlings.

Asimina triloba is sensitive to root disturbance. I don't know how well young seedlings can be transplanted. Asimina is best planted at its definitive place and not be transplanted.

I prefer pot grown seedlings PROVIDED that these are grown in deep pots ('oak pots' etc.) and are NOT pot bound.