I move mine twice a year the past few years (into the ground in spring, back to pots for winter,) and they get that tall. I think about 5 ft. would be the max under any conditions.
Here's a pic from about 20 yrs ago, the pot was about 8" tall. I think this is about 3 yrs in the same pot when I took this pic. Plants have been moved & repotted countless times since.
