The horseradish plant (Armoracia rusticana) provides an edible root that is the source of the pungent and aromatic herb called horseradish. Horseradish is one of the few herbs that can easily be propagated by root cuttings. For the home garden, one or two plants will provide a sufficient root crop. Started in the early spring, horseradish roots will be ready for harvest by fall; you can dig them throughout the winter as needed.
Dig up a mature horseradish plant in early spring. Take care not to damage the tuberous roots while digging. Cut sections of the roots that are around 8 to 12 inches long and 1 inch across. While it is not necessary, you may choose to use roots that bear buds. No other special preparation is required before planting the root cuttings.
Prepare your garden for planting horseradish roots in the spring. Ordinary garden soil that is moist and drains well works best. Choose a sunny area; horseradish will not grow well in shade.
Orient each root cutting with its top facing up. Place each cutting into the soil with the top of the cutting at least 2 inches deep. Set each planting about 2 feet apart to allow for growth as the season progresses.
Water the roots regularly to keep the soil moist but not wet. Once the plants have sprouted, fertilise them with a high-potassium, medium-phosphorus and low-nitrogen fertiliser.
Trim back any lateral growth on the plant back to one set of leaves once the plant is well-established. Called "suckering," this process will help the plant to form a more substantial root.
Pull each plant upward sharply to lift the roots after they have been suckered. Lifting each plant will break off early lateral root growth and encourage the main root to grow downward and become heavier, producing a single root that is easier to harvest and use.