It is best to harvest horseradish in the autumn, winter and early spring. To harvest, loosen the soil surrounding the plant using a digging fork. Gently clear out soil surrounding the largest roots, but do not yank the roots up, because they are easily broken this way.
Typically, a small portion of the season's growth is ready to be picked in early October, while the remaining annual production is ready in mid November, just before the ground freezes for the winter. The roots are ready to reap again in spring. Horseradish roots are best when they are about the width of a finger. Once harvested, rinse and dry the crops, and keep them refrigerated in an airtight container.