Root vegetables are sweetest and juiciest when harvested in cool weather.
Many root vegetables are considered “cool weather” crops—they grow lush and juicy when daytime temperatures are in the seventies, but barely muddle through hot weather. Which is why we plant them as early in spring as possible. But fall is just as suitable a growing season; this is when, in times past, we would be filling our “root cellars,” after all.
Source: Brian Barth, Aug 31, 2019 at https://modernfarmer.com