If using fresh horseradish, finely grate it or chop it in a food processor fitted with a metal blade. (If using the food processor, cut the horseradish into ¼-inch-thick slices before processing.) Whichever method you use, take care not to breathe the potent horseradish fumes.
Combine the grated horseradish, sour cream, herbs, lemon juice, lemon zest, salt, and