The ability of potato tubers to tolerate cold temperatures could be useful for maintaining the quality of tuber seed used for growing the crop, preserving the crop in storage, and germplasm preservation. Previous work measured the limits of survival of tubers of numerous populations of the wild tuber-bearing potato species Solanum jamesii (jam), native to the southwest USA in terms of ability to sprout after a -15C cold challenge. In that study, nine cold sensitive populations and nine very hardy populations were identified. In the current study, these two sets of jam populations were multiplied under field and greenhouse conditions and cold challenged along with Solanum kurtzianum (ktz), a species much more easily used in cultivar breeding with potential for cold tolerance shown in previous experiments. The results of this study were similar to previous ones: Tubers of jam started to die at -15C, with field-grown tubers hardier than greenhouse-grown tubers. Tubers of populations previously observed to be slightly less cold tolerant were not significantly different in the current more systematic trial. We conclude that tubers of S. jamesii populations available from the US Potato Genebank are all similarly very cold hardy. Most tubers of the 80 ktz populations sprouted after cooling to -8C, identifying this species as an additional subject for research and breeding.