There used to be a nursery in Harlingen, TX that sold kumquats on sour orange. The grafts would fail after a few years. Use Cleopatra mandarin, or trifoliate or one of the trifoliate hybrids for rootstock. I think Thomasville citrangequat should give a good cold hardy tree. Some have used Swingle citrumelo to get huge trees fast and lots of very sweet fruit. Swingle is less cold hardy than Thomasville but a lot more so than Citrange. I have a friend who grafts several dozen trees a year on feral trifoliates. He has given up on grafting kumquats as being too difficult. He only does a wedge-cleft graft. Commercial grafters use T-budding on trifoliate.

Hey guys don't fret too much about the occasional cool day and cold night. In Harlingen, TX, where the normal high and low for January is 68/49, I have seen green Malayans with about 5-7 ft. of wood and about 18ft. tall overall height and one last summer had a pretty big coconut about eight inches long growing on it! In Brownsville, I have seen 30ft. tall overall height Mexican Talls, and on South Padre Island, there is a Mexican Tall that the last time I was there in December, it had 47 coconuts total on it! Most were small to medium size, but about 4 or 5 of them were in the 8-9 inch range and will probably be about 10 inches by the time they ripen. Anyway, the Valley has some cool days, with highs in the upper 40's to lower 50's occasionally, and some nights in the 30's occasionally, and the coconut palms still grow and even fruit there. The problem is when you have prolonged periods of about 5 days or more when the temps are really cool, as is often the case this time of year in Southern California, and also when you have a hard freeze. Coconut palms can take the occasional cool day or two and even the occasional light freeze, but they can't take prolonged cool weather or hard freezes below about 27F, especially when they are young. P.S. I will try to get my photos of the above palms on to a disc this week so I can email them to any of you who might be interested.

They were shipped from Harlingen TX. Apparently that's in the Rio Grande valley. According to this recounting of Texas red grapefruit history, the only trademark names in use for Texas red Grapefruit at the moment are "Ruby Sweet" and "Rio Star." I've seen though, the informal proliferation of random names just as you say. Do you know if any of the Texas red varieties are known to grow a small-size grapefruit?

That’s a neat ‘unique evergreen’ list. I’m growing all of those plants in San Marcos. I have not planted guayacan in ground as I’m afraid it may not be cold hardy enough for my neck of the hill country. I plan to grow to a large size before planting out. Esenbeckia (limoncello) is beautiful and cold hardy, just really slow. It has endured upper teens temps and resembles a stocky, shrubby citrus. Mike Heep’s Native plant nursery in Harlingen, Tx sells nearly all of the plants on the list and has especially nice esenbeckias.