Stewartia leaf problem

[JeffS73]

Hi folks, I have this Stewartia that I'm guessing is an air layer, it just looks like a branch. However, the problem is, last year it leafed out OK, then the leaves reddened, and it didn't grow out any new shoots. This year, it's leafed out, and the leaves are reddening again. I thought it might be fert burn, I flushed it out last year. Advice please?

 

[JeffS73]

I should say, it's in a 1 gal deepish pot, organic mix and has been kept in the greenhouse, not too hot here.

 

[penumbra]

Looks like leaf scorch.

 

[bwaynef]

Looks like sunburn to me. But chlorosis too. Seeing as how I'm sunnier and warmer than the OP, that does make me think it might be nutrient related. What's your fert regimen? Soil? Water frequency/quality? Where's the tree situated and how long's it been there?

What's the part about the airlayer?