How tall will they get?

Last spring I bought two dwarf citrus trees, ruby red grapefruit and tangelo, in 5 gallon pots. I bought them because they are on Flying Dragon stock so should not get bigger than 8 feet tall & wide. They are doing very well in my small greenhouse and I want to set them out in the ground in the large greenhouse soon. This is in Northern Arizona where temps get down to 5 or 6 in the winter, and it snows.

Meanwhile, I bought a fixer-upper house in Apache Junction, a totally different climate -- hot & dry, but plenty of room for citrus trees. All I could find at the Big Box stores were labelled "semi-dwarf". The salesmen all assured me that this was the same as "dwarf" but the tags say they can get to 15 - 20 feet. (Liar, liar, pants on fire?) Anyway I bought 5 varieties for AJ and one AZ Sweet orange for my greenhouse up here ... and now I think putting the "semi-dwarf" in the GH with the Flying Dragon would be a mistake -- the ceiling is from 8 to 10 feet high. Also, down in AJ, I planted the citrus the same way I would have up here in the greenhouse, 8 feet apart, but that is probably a mistake too.

So what do you think? Should I take the AZ Sweet orange down to AJ, and then move them all 15 feet apart?

Eight feet even on Flying Dragon rootstock is a bit optimistic. Flying Dragon cuts the size by about 1/2. Given that some 'standard' citrus trees can grow to 25' - 35', 12' - 15' may be more realistic. Your greenhouse ceiling may need to be higher or you will have to do a lot of pruning — something not usually recommended for citrus. To make up for the height you will be cutting off as they get larger, you could let them take on a more rectangular quasi- espalier shape. So moving them 15' apart would make sense.

Thanks, but Treeland Nursery in Chandler, where I bought the two trees on Flying Dragon rootstock, says on their website that they only grow from 6 to 8 feet for the tangelo, maybe up to 12 feet for the grapefruit. So if and when the grapefruit threatens to push the GH ceiling up, I will have to prune it. 8^) When I lived in Scottsdale I had mature citrus trees (pink grapefruit, tangelo, valencia orange or maybe it was AZ sweet, navel orange, and lisbon lemon) so I know they can get HUGE.

I realize that I inadvertently failed to mention that the newer "semi-dwarf" trees I bought were on C-35 rootstock.

So maybe my question should have been, does anybody know the difference between Flying Dragon and C-35 rootstock?

Uh oh, I was wrong about the tangelo. Treeland says it will grow to 8 to 12 feet, same as the grapefruit. But they are slow growing!

Flying dragon root stock is the preferred root stock where I am and they will get more like 12X12 if planted in the ground. Semi dwarf can be more like 20 feet high.

Maybe this will help. http://edis.ifas.ufl.edu/hs221

This one has info on many root stocks and C-35, http://edis.ifas.ufl.edu/hs196

Thanks, Core, that's usefu info.