The decline in temperature with increasing elevation and latitude is the primary determinant of the cold distribution limits of organisms. In temperate tree species, growth limitation by low temperatures during the growing season is widely recognized as a key factor shaping species-specific cold range limits, but the mechanistic understanding of the underlying physiological processes remains incomplete. One potentially fundamental mechanism is reduced cellular turgor resulting from insufficient root water uptake in cold soils, which may constrain the growth of the entire tree. Negative effects of low, non-freezing root temperatures on plant hydraulic functioning have been recognized since the beginning of modern plant physiological research. Nevertheless, these effects have received surprisingly little attention in the context of a functional explanation for the cold distribution limits of trees. Cold soil-induced hydraulic constraints arise primarily from the resistance to radial water transport in fine roots, which increases exponentially with decreasing temperature and substantially limits root water uptake in temperate trees at around 5°C, a temperature threshold previously recognized as the global limit for tree growth. Recent experimental studies have shown that species-specific differences in the sensitivity of root water uptake to low temperatures are negatively correlated with the natural upper elevation distribution limits of temperate tree species. Although these relationships are largely correlative, they strongly suggest a causal link between a species’ capacity to acquire water from cold soils and its cold distribution limit. In this review, I synthesize current knowledge on the negative effects of low root temperatures on plant hydraulic functions and discuss the physiological mechanisms underlying interspecific variation in the cold sensitivity of root water uptake, with a particular focus on the role of aquaporins for the symplastic pathway of radial root water transport. I summarize previous empirical evidence, derived from greenhouse and field studies, for cold root-induced hydraulic constraints in temperate trees, which demonstrate marked declines in tree water potential and growth at root temperatures between 10 and 0°C. Finally, I discuss how incorporating the effects of cold soils on tree hydraulic functions can complement existing functional hypotheses for the cold range limits of temperate trees and outline future research directions aimed at improving predictions of soil temperature effects on tree productivity and distribution.