The rootstock can provide its scion with several qualities:
1. Cold hardiness. In areas where citrus is grown outdoors, but where frost is a potential problem, this can be important. While no stock gives extreme hardiness (no, youll never be able to grow orange trees outdoors in Ohio!), the difference can be several degrees of hardiness. On the other hand, some stocks reduce the hardiness of the scion. In approximate order from most cold-hardy to least, here are the common stocks used in Florida and California:
Poncirus trifoliata (including Flying Dragon), sour orange, sweet orange, citrumelos (including Swingle). These three enhance cold-hardiness noticeably.
Carrizo and Troyer citranges; Cleopatra, Sun Chu Sha, and other mandarins. These stocks have little effect, one way or the other, on hardiness.
Rough Lemon, Volkameriana, Rangpur. These stocks may give a tree that is less cold-hardy.
2. Tolerance to disease problems.
3. Enhanced (or diluted) flavor.

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