From Little Minneapolis Forum
NDSU Extension Horticulture Don Kinzler:
Q. This is the first year that I've grown horseradish. When is the best time to dig it?—D. Larson, Bismarck, N.D.
A. Horseradish is a winter-hardy perennial like rhubarb and asparagus. Commercially it's often grown as an annual and replanted each year. Roots and shoots are carefully trimmed and side-pruned to produce single large-diameter roots for ease of handling and commercial peeling instead of numerous smaller-diameter branched roots.
Most of us who enjoy growing horseradish in the garden grow it as a perennial, locating it at a side or corner of the garden where it can remain in a permanent spot. Because much of its root enlargement occurs in late summer and fall, horseradish is best left in the ground until after several hard frosts, but before the ground freezes solid. Late October is usually good.
The deep roots of horseradish make it possible to dig and harvest the main root, leaving enough root intact underground to rebound next spring. For good measure, I usually replant a pencil-sized side root back into the hole after digging, just to be sure I didn't remove the whole root system.
