Or at least do they do this outdoors in colder climates?

I have one behaving this way, though it has a few other complications.

A single main flush seems possible because Poncirus is deciduous in the colder parts of its range.

As indicated in your above posting ( though it has a few other complications.) Maybe one, of a few problems preventing this.

Citrus are always active in growing, 2-4 months roots, 2-4 months top growth. although cooler or very hot weather may slow the process. Regards Tom

~8 feet tall
-Grown for years (fruiting) in a 25 gallon pot
-Transplanted this spring, after first flush
-Transplanted bare root (a few hours out, roots in damp sawdust)
-Trimmed much of the new flush off when de-potted to reduce water needs after transplanting.
-Been very hot.
-Shade in morning for first month or so, then those trees removed several weeks ago.

It has been watered and gently fertilized.

It was so far into other plants for those other years that I simply never noticed (or remembered) whether it had later flushes in the summer.