Horseradish (perennial vegetable) is classed perennial in the cited extension guidance. The timing rules below are relative to your local freeze dates — enter a location to turn them into calendar dates.
The rules this site applies
Method
Frost-relative window
Rule & reconciliation
Transplant outdoors
6–4 weeks before the median last spring freeze
Purdue Extension HO-186-W Table 1 places horseradish in the group headed "Hardy (tolerates hard frost) plant 4-6 weeks before last spring frost," and footnotes it as typically vegetatively propagated, so the six-to-four-week pre-frost window is applied to setting out root cuttings rather than to seed; no other extension source located gives a frost-anchored horseradish planting date, so there was nothing to reconcile against.
Variety assumption: Assumes planting purchased root cuttings or sets of a standard variety such as Common or Bohemian, lifted the following fall after frost.