Steve
Thanks for the endorsement in my continuing quest for international certified curmudgeion; but the thumb up, 360 degree test is still the best for me.

I suspect sour orange, C35, even Carrizo would do well there; I would opt out of dwarfing/semi-dwarfing rootstocks, as your climate alone will create that affect. Poncirus is an acceptable choice, but not noted for aggressiveness or hardiness.

Steve most of mine on c35 do better.
Trace

Hi John , Tracy.

Thanks for getting back. It is clear that my kumquats are going no where on their own roots. I may get a grafted kumquat tree when I travel south, but now I keep mine untill they die. I have found homes for 2 of my trees now.

Steve

If you want to push kumquats, try Swingle citrumelo, but they don't like wet feet. If you use TX/ northern Mex sour orange they will fail after a few years. One ref says tresteza virus free sour orange will be compatible, but I don't think that is available in the US. I know of no rootstock that satisfies all your conditions. I am growing six different ones now. C-35 is not best as cold tolerant.

One you may try is keraji mandarin, fast growing and very tough. Good cold hardiness if you don't fertilize after June, it would be an experiment though.