Re: Flying Dragon-Poncirus triifoliata
You certainly can't count on buying a citrus and having 'Flying Dragon' as a rootstock. As far as "why" I can answer that as the only citrus for zone 6 are the straight species Poncirus trifoliata and 'Flying Dragon'. I grew some from seed and they didn't really have the form I was hoping for. I think they require a lot of pruning to keep them from being either gangly or bushy. I sold one a year or so ago but all I have left are really too tall to ship.