Well, I’m never quick to dismiss old wives’ tales, because some of the best gardeners I’ve known have been old wives. Gardeners who enjoy growing carrots have long known that delaying digging as late as possible in the fall makes them taste better.
If this is true, what is it about frost that sweetens carrots? The University of Wisconsin offers a very good explanation. It’s a phenomenon called cold-sweetening. Through photosynthesis, plants store energy as starches. But when temperatures grow colder, some plants, such as carrots, convert starch into sugars, which they store in their cells to protect against frost damage. Sugar dissolved in a cell makes it less susceptible to freezing, almost like a plant’s antifreeze. Not only does it delay plants from freezing, but they taste sweeter too.
So yes, it’s true: delaying digging carrots until we’ve had frosts and cool temperatures does make them sweeter. Carrot harvest can wait until right before the surface of the ground freezes solid. Some old-time gardeners covered the carrot rows with a deep layer of straw before soil freeze-up, and could dig fresh carrots well into winter.
When carrots are dug, the best long-term storage temperature is 32-34 degrees F. with high humidity, often termed cool-moist storage.