Horseradish is a perennial in zones 5-9 and an annual in other zones. It belongs to the same family as cabbage and mustard plants. The root has a strong aroma, that when cut breaks down enzymes, causing an irritant to eyes and sinuses. Grated roots are used immediately or mixed with vinegar to preserve the pungency and eliminate bitterness. Roots left in the ground unattended for too long become woody. Although technically a vegetable, leaves are rarely consumed, so the plant is considered an herb.
Plant in well-draining soil with compost and a nitrogen fertilizer after all signs of frost are gone, or in late fall for a spring harvest. Horseradish prefers sun and temperatures around 60 degrees; over-watering causes root rot. Confine this aggressive plant by cutting the bottoms out of pots, placing pots in the ground, and containing the root within the pot. Horseradish is a sterile plant and cannot be propagated through seed—only root cuttings.