High Altitude Rhubarb sells two varieties of horseradish, an heirloom variety and one of unknown origin. The roots, which are the edible part, are very similar. Horseradish is highly adaptive. Will grow in many soil types and climates. Be warned, however, that it is invasive. Plant it too close to your house and it will be popping up in your living room before you know it! The plants are extremely hardy, too. Easily split and transplanted.
Horseradish is generally harvested in the fall but can be dug any season. By fall, each plant present that spring will have produced at least one other plant through roots. To harvest, dig up the entire plant and take the largest, oldest root. Replant the smaller roots, amending the soil if you like. The plant is so vigorous, however, that it usually won’t matter if you replant any roots. New plants will soon emerge from root fragments left in the ground. For a new planting it is recommended the first harvest be no sooner than fall of the following year.