Loosely coiled, off the concrete.

Coil it loosely and keep it off the cold ground.

Cold weather makes PVC insulation brittle, so the real enemy is stress—tight coils, kinks, or hanging from a nail all create weak points that crack when you flex the cord in spring.

If you can bring the cord inside for winter, do it. A garage or basement is fine. If it has to stay outside, coil it in wide loops (at least 12 inches in diameter) and lay it on a shelf or a dry board, not directly on concrete or frozen dirt. A figure-eight coil is even better—it prevents sharp bends at the ends.