olive tree

 About four three years ago, I bought a small potted olive tree at the Eden
Project.  It has done amazingly well and now quite a lot bigger.  Every
summer I leave it in the garden and it flourishes.

I have just brought it back inside as the evenings and mornings are now a
bit cool for it, and I have found alot of the leaves are going yellow and
falling off.

I don't remember this happening before, any ideas?

Frances