The best substitutes for horseradish include wasabi paste and black radishes. Wasabi paste, which is made from domestic horseradish varieties, is not as pungent as fresh horseradish, so it may take more paste to achieve a similar flavor. Black radishes have a different flavor but contain a similar heat level.
Other substitutes include grated ginger or spicy mustard. While these ingredients can provide a similar level of heat, they also alter the flavor of the recipe. When a recipe calls for fresh horseradish, commercially-prepared horseradish or horseradish sauce, which is made with a sour cream or mayonnaise base, can be substituted. Most grocery stores place prepared horseradish in the deli or meat department.