Horseradish (Armoracia rusticana) is a large leaved, hardy European perennial herb that has been a culinary favorite for more than 3,000 years. Horseradish was used in England long before the Romans introduced the English to other herbs and spices.
This fiery herb thrives in temperate climates and in the cool, high altitudes of tropical countries. Horseradish grows best in deep, rich, moist loamy soil, in a sunny location. Roots tend to be malformed and yields are reduced on hard, shallow, stony soils.
Before planting horseradish, spade or rototill the soil to a depth of 8 to 10 inches, turning under or mixing in generous amounts of well-decayed compost or other organic material. Incorporate either a complete garden fertilizer (10-10-10) at a rate of one lb. per 100 sq. ft. or a liberal amount of well-decayed manure into the soil. Fresh or partly fresh manure used before planting will cause excessive top growth and forked roots. Let the worked-up soil settle a few days before planting.
Plant root cuttings, sometimes called "sets", in early spring as soon as soil can be worked. Space the sets 1 foot apart, setting them vertically or at a 45 degree angle. If angled, make sure that the tops point along the rows in the same direction. This makes cultivating easier. Cover the sets with 2 to 3 inches of soil.
Weed control is especially important early in the season when the plants are relatively small. It is best to cultivate in the same direction that the sets were planted. Mulch around each plant with organic material such as compost or leaves. It will benefit the plants by retaining moisture in the soil, keeping the soil cooler, and controlling weeds.
To grow high quality horseradish, lift and strip the roots twice, first when the biggest leaves are 8 to 10 inches long and again 6 weeks later. To lift and strip, carefully remove the soil from around the upper ends of the main root, leaving roots at the lower end of the set undisturbed. Raise the crown and remove all but the best sprout or crown of leaves. Rub off all small roots from the crown and sides of the main root, leaving only those at the bottom. Return the set to its original position and replace the soil.
Horseradish makes its greatest growth during late summer and early autumn. For this reason, delay fall harvest until late October or early November, or just before the ground freezes.
Harvest by digging a trench 12 to 24 inches deep along one side of the row. Then, working from the opposite side of the row with a shovel or spading fork, dig the roots. Use the tops as a handle for pulling them laterally from the soil. Trim the green tops so there's only one inch left. Trim off side and bottom roots saving those that are 8 inches and longer for next spring's planting stock. Cut the roots squarely across at the top and sloping at the bottom. This will make it easier to distinguish which end to set upright at planting time.
Tie cleaned root cuttings in small bundles and place them in moist sand. Overwinter horseradish in a root cellar or basement that stays between 32 and 40 degrees during the winter. The roots must not be exposed to light, otherwise they become green. If storage and temperature conditions cannot be met, an alternative would be to harvest horseradish in spring rather than fall. Dig the roots as soon as new growth starts to appear in spring. Replant lateral roots for next spring's crop. Roots left in the ground for two growing seasons become stringy and woody.
Storage & use
Store horseradish roots for fresh grinding in dark plastic wrapping in the refrigerator. Protect the roots from light to prevent their turning green.
The most common way of preparing horseradish for table use begins with peeling or scraping the roots. Grate the root directly into white wine vinegar or distilled vinegar. Avoid using cider vinegar, as it causes discoloration in the grated horseradish within a rather short time. Depending on your preference, the vinegar may be slightly diluted. Bottle the horseradish and cap the containers as soon as possible after grating. Refrigerate at all times to preserve the pungent flavor. Freshly grated horseradish will keep only for a few weeks. Then prepare a fresh supply.
Horseradish may also be dried, ground to a powder and put up in bottles in a dry form. Dried horseradish will keep much longer than the freshly grated product, but is generally not as high quality.
Occasionally, horseradish may suffer from root rot. Select only disease-free root cuttings to use as planting stock. Rotate the planting site so horseradish is not grown in the same place more often than every 3 to 4 years.
The horseradish flea beetle is a serious pest on horseradish foliage. It deposits egg clusters on leaf petioles. Its larvae burrow into the petioles and kill some of the leaves. Sprinkle wood ashes lightly on the plants to repel the beetles. Good sanitation practices in the garden are the best insect prevention.