Virginia Vegetable, Small Fruit and Specialty Crops - November-December 2005
Horseradish is grown primarily as an annual crop in most temperate climates, and to a limited extent in short season regions, as a perennial crop. As an annual it requires a long growing season, with warm temperatures needed during the vegetative phase, followed by cooler temperatures in late summer and fall that enhance root development. In the annual system the crop is planted in the previous fall or early spring, and the entire root mass is harvested after the first killing frost. In the perennial system, upright, thickened, underground shoots arising from a deeply planted "mother" root are harvested every other year, with the original plant left in the field for regeneration. Perennial fields may stay in production for 10-20 years. Horseradish has wide climatic adaptation, with the exception of the warmer zones of the far southern United States. Historic areas of U.S. production include Illinois, Wisconsin, California (northern), Oregon and New Jersey, where 3500-4000 acres are harvested annually.
There are numerous strains of horseradish. Depending on your site, one or more may perform better than others, and observations on adaptability should be made. Important indicators for performance include development of large primary root diameters and a solid white root interior with no discoloration. The outer root surface should not be too rough, but smooth skinned and straight, with little crevicing, corking, cracking or rootlet "fuzzing" (Fig. 1). A smooth above ground crown (head) texture, and low shoot numbers are also desirable. Roots should be hot, but slow to develop, with some hint of sweetness. As superior strains become evident, it is important to make an effort to keep planting stock sorted and separated, as roots have a similar appearance and are easily mixed.
Many variations occur in leaf shape, size and texture. Horseradish is divided into two general types, "Common" and "Bohemian". Maliner Kren is a "Bohemian" type from which many selections have been made. The "Common" types have broad crinkled leaves and are considered to have superior quality, while "Bohemian" types (Fig. 2) have narrow smooth leaves, somewhat lower quality, but better disease (Turnip Mosaic 1; White-rust, Albugo canadensis) resistance.
Obtaining adequate quantities of quality planting stock is a major concern in horseradish production. Horseradish is propagated vegetatively by making a root cutting, (set), _ to1 inch diameter, and 7-15 inches in length. In the annual system, this set enlarges and becomes the primary marketable product at seasons' end, along with the many secondary roots forming along the medial and distal regions. At fall harvest, sets for the next year are "pulled" from these new branched roots arising from the spring-planted, original set. Cut the sets to desired length, trim off all tertiary rootlets and forks, and then store them over the winter for the next season. Because horseradish roots exhibit distinct polarity, and since the diameter is often similar for the length of the root cutting, trim sets straight across at the top (head) and oblique at the lower end (tail) to mark the polarity. Pack the sets uniformly by head / tail polarity in wooden or plastic storage crates lined with heavy plastic. Loosely seal the plastic to cover the sets, and keep in cold storage at 35-40o F until spring. Underground storage pits or caves can be used in lieu of modern coolers. There is no vernalization (chilling) requirement, and sets can be planted anytime after separation from the main plant.
1-2 lbs/acre of boron should also be broadcast with the fertilizer, and if sulphur levels test low on the site (<10lbs/acre), apply 15-25lbs elemental sulphur /acre. Though this is a low level of sulphur application, it may decrease soil pH, which should be monitored for future crops.
Supplemental nitrogen application of 50-75lbs/acre should be made 8-12 weeks after planting. It can be broadcast or banded near the row for greater efficiency. Over application of nitrogen may lead to hollow roots, and can promote top growth at the expense of root development, particularly when applied too late in the season.
Depending on soil moisture holding capacity, irrigation during dry periods, particularly in late summer to fall, can improve marketable yield. Studies have shown that most main root sizing occurs during the mid to late fall period, and not during the summer.
For weed, insect and disease control guidelines, consult the Commercial Vegetable Production Recommendations (pub#456-420). Only a few herbicides are available for use in horseradish. Because of relatively short residuals, supplemental weed control during the long growing season with tractor cultivation and/or hand hoeing is often needed. Some varieties / strains are sensitive to downy mildew and white rust, but application of recently registered fungicides can help keep these and other leaf diseases in check. Horseradish is highly susceptible to a disease known as Brittle Root, (Spiroplasma citri) a virus-like disease that is transmitted by the beet leafhopper. A program of scouting for this insect and application of approved insecticides will reduce or eliminate incidence. In recent years, areas of commercial production have been affected by incidence of root discoloration, with the primary causual agent identified as a Verticillium species. Care should be taken to inspect planting stock for any indication of discolored, streaked or internal flecking; these roots should be discarded. There is no "certified" program in this country as done with other vegetatively propagated crops.
In general, foliage feeding by insects is of minimal concern, as horseradish can tolerate a significant amount of early flea beetle and worm damage before yield is decreased.
The advantage of lighter textured soils quickly becomes evident during harvest. Lighter soils dry more quickly allowing field access in wet winter months and they are less likely to adhere to the root mass. Harvesting usually leaves many broken root pieces behind. These over-winter and sprout the following season as "volunteers". Control of volunteer horseradish in successive crops is important, as it can become a serious weed problem; and volunteers negate benefits of effective crop rotation. Harvest is often delayed until spring, when digging of the old crop and planting of the new crop may occur at the same time.
After harvest, the wagons are brought in to a sorting shed. The roots can be cleaned in a revolving cylinder, where excess soil is tumbled off (Fig. 3), or they can be shaken free of soil by hand. Leaf and petiole residues remaining on the crown should be trimmed closely by hand with a knife or with some type of mechanical trimmer. Roots making #1 grade size and shape should be trimmed from the rest of the root mass, and marketed at a premium (Fig. 4).
Usually roots are not washed. For "wild-root" grade used for processing, the entire root mass is marketed by weight. By using a retractable, hinged box, masses of root can be formed into cubes, film wrapped and shipped on wooden pallets to processing plants. Pack large, #1 roots separately from "wild root" in 50-100 lb. burlap sacks. The #1 roots can be cleaned (tumbled) with water to remove the rough outer layer, and put in small plastic packs (usually 5-10lbs) for retail grocery trade.
Yields will vary by site, variety used, and culture, but expect on the low end 3000 and the high end up to12,000 lbs harvestable root mass per acre. Prices are variable from year to year, with wild field run root ranging from .25-.50 cents/lb, and #1 root approaching $1.00/lb. Specially packed, washed and tumbled, white #1 root can bring significantly more in the grocery trade, depending on market demand.
The requirements for marketing #1 root are: A well-flavored root, reasonably straight, without side shoots, and no mechanical or decay damage. The roots should be at least 8 in. long with a diameter of not less than 0.75 in."
In conclusion for the smaller scale grower, horseradish has potential marketing outlets through fresh sales to local grocery and specialty food stores, and to specialized food processing companies. Direct marketers who have approved kitchen facilities can add processed horseradish to their line-up of value-added products.
For larger scale production, it is common for condiment processors to work on a contract basis with growers. Historically these relationships go back many years, with the processor used to a certain quality and type of root, which can vary greatly between varieties and the farms that raise them. Thus very little "open market" sales are conducted for bulk processing root. In short, this market can be difficult to break into and existing growers are protective of their markets. Sales of #1 roots to larger grocery chains, through brokers, may be a more easily accessed and open market for the new grower.
Fig. 1. Primary root with smooth surface texture (image by C.C Doll)
Fig. 2. Horseradish plant, smooth leaved Bohemian type (image by Bratsch)
Fig. 3. Horseradish roots being tumbled and packed (image by Bratsch)
Fig. 4. Grocery display of whole roots (image from Purdue Dept. Food Science)