Place the beets in a saucepan and cover with cold water. Bring to a boil, reduce the heat and simmer the beets, loosely covered, for 25 to 30 minutes, or until easily pierced with a fork. Drain the beets, reserving 2 cups of the cooking liquid. When cool enough to handle, rub the skins off.

Slice the beets into strips and place in a 1-quart jar, along with the onion and garlic. In a saucepan, combine the vinegar, sugar, cardamom seeds, cloves, salt, and the reserved cooking liquid. Heat just enough to dissolve the sugar, while stirring. Pour warm vinegar liquid over the beets, onion and garlic in the jar. Let cool to room temperature, then cover, and refrigerate overnight. (Pickled beets will keep for 1 week in the refrigerator.)

In a large bowl, combine the pickled beets, gherkins, and apple. In a small bowl, blend together the horseradish, sour cream, salt, and sugar, and add to the pickled beet mixture. Stir gently, cover and refrigerate. Serve salad chilled.