Growing Horseradish (Armoracia rusticana)
Horseradish (Armoracia rusticana) will spread and live for years, so pick a location with that in mind. Plant in full sun and in soil that is slightly acid (pH of 6.2-6.7). Break up the soil to a depth of 8in and work in several handfuls of compost. Dig a hole 4-6in deep and place your 6in root cutting at an angle with the slanted, cut end down and the top of the root 2in below the soil line. Placing the root at an angle encourages more roots to develop along each cutting. Space roots 10-12in apart with 3ft between rows.
Until your plant becomes established, water when the top 1in of soil is dry. Keep the area around your plant free of weeds. After the first year, fertilize in spring with a balanced, 10-10-10 fertilizer or top-dress with compost.
Harvest roots in the fall starting the second year after planting. Dig up a piece of root about the size of a carrot, wash it well, and then scrape it under water to avoid eye irritation. The whole root can be stored in a plastic bag in a refrigerator crisper for several months. Grate the root outside on a breezy day, or use a blender in a well-aerated kitchen -- it's powerful when really fresh. Once grated, mix with just enough vinegar to cover and add salt to taste. Refrigerate in a glass container with a tight fitting lid.
Plants can be divided about every 2 years in spring as soon as the ground can be worked. A piece of root about the size of a carrot is sufficient to start a new plant.