Final answer:
Tall fescue is more low-temperature hardy than St. Augustinegrass, making it the better choice for cooler climates, although specific varieties may vary in cold tolerance.
Step-by-step explanation:
The grass with greater low-temperature hardiness between St. Augustinegrass and tall fescue is tall fescue. St. Augustinegrass is known to be sensitive to cold temperatures and may suffer damage during periods of frost, while tall fescue is much more tolerant to low temperatures and can thrive in a variety of climates, including cooler ones. The resilience of tall fescue to colder climates is part of why it's often preferred in temperate regions where temperatures can drop significantly. However, it's also important to note that within species, specific varieties may offer differing levels of cold tolerance.