Ideas?
Sure, got choke ideas.
Just not about that.

About that, all I got is a wild-ass guess.
I think the trouble stems from the roots.
I see some lumber in that soil.
If the tap root hits one of those chunks directly it will stunt the plant.
If the root system is sub-par it will act like it's root bound.
At least, that's what it looks like to me.

But I'm quite likely mistaken.
I'm not a good diagnostician of plants.
Seems most of the really good mentors got banned from here.

They are now frequenting other sites. Happily helping folks like me.
All that's left of this formerly great board is some excellent archives and a very few old timers.
Maybe google Rusty Tricomb, or Old mac?

Aloha,
Weeze