Armoracia rusticana aka Horse Radish

Armoracia rusticana, or horseradish, is a perennial in the mustard family. Its native range runs from southern Ukraine to southern European Russia. People now grow it in many parts of the world. It forms an upright clump with thick, fleshy white roots. Sources give different sizes for plants grown in gardens. Smaller plants reach about 2 feet [0.6 m] tall and wide. Larger plants reach 5 feet [1.5 m] tall and 4 feet [1.2 m] wide. The roots spread underground and can form dense colonies.

Large, glossy, dark green leaves grow from the plant’s base. These simple leaves have toothed edges and resemble dock leaves. The largest reach 2 feet [0.6 m] long. Leaves grow smaller as they rise along the stem. The green stems are smooth and lack hairs. Leaves die back in winter, then roots send up new growth. Small white flowers have four petals and form branched clusters. Sources place flowering from spring through summer, depending on location. Bees, flies, and beetles pollinate the flowers. Oblong seed pods follow, with up to eight seeds each. Plants seldom make viable seed in cold winter climates.

Horseradish grows best in full sun but accepts partial shade. Give it deep, fertile, moist soil that drains well. It grows in clay, loam, sand, and chalk. It also accepts acid, neutral, and alkaline soils. Lighter soil makes the roots easier to lift at harvest. Rich soil helps produce larger roots with a stronger taste. The plant prefers places with cool summers. Sources place it in USDA zones 4–9 and UK rating H6. Gardeners often plant root cuttings in spring and harvest in fall.

Its main garden use is as a root crop. Grated roots add heat to sauces, relishes, and seasonings. Cutting the roots releases the oils that give this heat. Leaves and seeds are also listed as edible parts. Use roots in small amounts; large amounts can cause poisoning. Roots and leaves have a history of medicinal use. Reported cautions include stomach ulcers, thyroid problems, and several digestive conditions.

Fast growth makes this plant hard to contain or remove. Even small root scraps can grow into new plants. An isolated vegetable bed helps keep it from crowding neighbours. Cabbageworms, mustard leaf beetles, and flea beetles may eat leaves. Club root can also affect it, though serious problems are uncommon.