Kale is a hearty vegetable that prefers the cold weather, and if cared for correctly can produce a surplus of leaves throughout every season, including the winter. The time frame for harvesting kale is a personal decision, loosely based on flavor preferences. For those that require a lighter side to kale's taste, younger leaves will suffice. But for those that like the more pungent and bold flavor of kale, the matured leaves of fall are preferable.