The suggestion that kumquats do not grow well on their own roots is often mentioned. It appears to be attributed to Julia Morton's writeup in her book, Fruits of Warm Climates. (Reference: http://www.hort.purdue.edu/newcrop/morton/kumquat.html) I'm not disputing this conclusion but is it supported by any other sources? By actual grower experience? Does the result depend on whether the tree is grown in ground or in container?

Good question. My Centennial kumquat is a root cutting & has never had a problem (Inground)