The best time to harvest horseradish roots is in the late fall and early winter, after frosts but before the ground fully freezes. In areas where the ground does not freeze, gardeners can harvest horseradish throughout the winter. A spring harvest is also possible after the ground thaws.
Any horseradish left in the ground sprouts in the spring, and large, inedible leaves form throughout the summer. The plants start boosting root growth in late summer and continue into early fall. Although gardeners should allow their horseradish to grow for a full season, roots develop an undesirable texture after spending two seasons in the ground.