To control its spread, remove the entire root, including any branches, when harvesting, then replant only only a modest amount of roots, just enough to meet the following seasons needs.
Horse Radish also can be grown in a deep planter. Growth is usually somewhat slower. Soil pH should be between 5.5 to 7. The horse radish plant will grow approx. 24" tall and 18" wide, so be sure to use a large enough planter.
Horseradish can be grown from root cuttings or plants and can be set out in early spring or fall. Loosen the soil to about a foot deep and add a shovel full of compost to the hole. Plant the root cutting upside down at an angle, with the top of the cutting about 2 inches below the ground. One or two plants is generally sufficient to meet the average family needs for a year. Should you plant more, they should be spaced about 2 1/2 feet apart.
It is perfectly normal for the horseradish plant to wilt after planting, especially if planted in full sun, temporarily shading the plants for the first couple of days is advisable until they recover from transplanting.
Horseradish doesn't require extensive attention once it's growing. Water weakly bi weekly, slightly more during dry spells. A few of inches of mulch around the plant base is advisable in order to conserve moisture.
The compost you originally placed in the planting hole should supply the horseradish plant most of the nutrients it needs for the season. If absolutely necessary apply a low-nitrogen fertilizer occasionally, no more than 3 times per season. Soil pH should be 6.0 -7.0.
Fresh horseradish leaves are a spring treat, best harvested before summer sets in. Young leaves are subtle and tasty, older leaves of summer are tough and spindly.
Your first horseradish harvest should be one year after planting. Dig away the soil from around the tap root, careful freeing up the side roots and removing them simultaneously. For optimal yields, harvest after the frost has killed any foliage. Scrub the primary root with clean running water and dry well. Horseradish root will keep in a refrigerator for three - four months.
Both the leaves and roots of horse radish plants are edible, the leaves are less commonly used. See Preparing & Preserving Horseradish