Common Name: Horseradish

General Information

Armoracia rusticana is a herbaceous, perennial plant growing from a long, fleshy, cylindrical taproot. It produces a cluster of erect basal leaves up to 100cm tall and a flowering stem up to 150cm. The plant produces long secondary roots and subterranean runners from which new taproots develop, the plant spreading from its second year of growth onwards to form a large clump[, ].
Horseradish has been cultivated for over 2,000 years for its fleshy root which is used as a food flavouring and also medicinally. There are some named varieties[, , , , ].
A very invasive plant that can be very difficult to eradicate, it is considered to be a pernicious weed in some areas[]. Even quite small sections of root will regrow if they are left in the soil[, , ].

Known Hazards

The plant, and especially the roots, contain glucosinolates. In small quantities, such as when the root is used as a condiment, these can be a very healthy addition to the diet, but in large quantities they can be somewhat toxic, producing profuse sweating, irritation of the stomach and intestines, loss of strength, disorientation[].
Large quantities of this plant can be poisonous due to its content of volatile oils[].

Botanical References

Range

Probably eastern Europe (Moldova), though it is widely naturalized in many parts of the world.

Habitat

Arable land, waste ground and by streams[], favouring slightly damp positions[]. Fields, moist stream banks, roadsides, ditches, disturbed sites, open woods, along railroads, shallow ponds, marshes, waste places; at elevations to 1,100 metres[].

Properties

Weed Potential	Yes
Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Perennial
Height	0.70 m
Pollinators	Bees, Flies, Beetles, Self
Self-fertile	Yes
Cultivation Status	Wild

Cultivation Details

Horseradish is widely distributed through the temperate zone, mainly as a result of cultivation, and can also be cultivated at elevations above 1,000 metres in the tropics. It grows best in areas where annual daytime temperatures are within the range 14 - 20°c, but can tolerate 6 - 28°c[]. When dormant, the plant can survive temperatures down to about -15°c, but young growth can be severely damaged at -1°c[]. It prefers a mean annual rainfall in the range 600 - 900mm, but tolerates 390 - 1,700mm[].
A very easily grown plant, horseradish prefers a good deep moist well-drained soil and a sunny position[, , , ]. Plants require a good soil if they are to produce good roots[], though once established they are very tolerant of neglect and will continue to produce a crop for many years[, ]. Plants do not thrive if they are in the shade of trees[]. Excess nitrogen causes heavy top growth and forking of the roots[]. Prefers a wet clay soil according to one report[], whilst another says that it will not grow in wet clay[]. Prefers a pH in the range 6 - 7, but tolerates 4.5 - 8.7[].
Yields of around 7.5 tonnes per hectare per anum of primary roots (for use as a condiment) can be obtained, plus around 4.9 tonnes of secondary roots (for extracting the active ingredients or medicinal use)[].
The plant is very hardy and can be left in the ground all winter to be harvested as required[]
If the roots are given some protection they will produce fresh young leaves for the salad bowl all through the winter. Digging up some roots and putting them into a greenhouse for the winter is the easiest method. If the young shoots are blanched they will produce white, tender, sweet leaves[].
The plant has yet to prove invasive on our Cornwall trial grounds, though it has survived and even prospered in a very overgrown site[].
The forms of this plant grown in gardens are almost sterile and seldom produce good seed[].

Edible Uses

Young root - raw or cooked. The grated root is used to make the condiment 'Horseradish sauce'[, , , , , , , ], this has a hot mustard-like flavour[]. The sauce is best used uncooked or gently warmed, heating it will destroy the volatile oils that are responsible for its pungency[]. It is said that in Germany the roots are sliced and cooked like parsnips[] - rather them than me![]. The root is a rich source of sulphur[]. Fresh roots contain the glycoside sinigrin - this is decomposed in the presence of water by the enzyme myrosin, producing mustard oil which gives the root its hot flavour[]. The fleshy roots can be up to 60cm long and 5cm thick[]. The roots can be harvested in early winter and stored for later use - they will retain their juicy state for some time if stored in dry sand[].

Young leaves - raw or cooked[, , , ]. A very strong flavour, though nice when added in small quantities to the salad bowl[, ]. A pleasant mild flavour according to another report[].

Seeds - sprouted and eaten in salads[].

Medicinal

Horseradish is a very pungent stimulant herb that controls bacterial infections and can be used both internally and externally[]. The plant is a powerful stimulant, whether used internally as a spur for the digestive system or externally as a rubefacient[]. It should not be used internally by people with stomach ulcers or thyroid problems[].

The roots are antiseptic, aperient, digestive, diuretic, expectorant, rubefacient and stimulant[, , , , , ]. They should be used in their fresh state[]. An infusion is used in the treatment of colds, fevers and flu and is of value in the treatment of respiratory and urinary tract infections[]. A sandwich of the freshly grated root is a traditional remedy for hay fever[].
A tea made from the root is weakly diuretic, antiseptic and expectorant[].
Applied externally, a poultice made from the roots is used to treat pleurisy, arthritis and infected wounds[]. It will also relieve the pain of chilblains[]. Some caution should be employed, however, because it can cause blistering if left on the skin too long[].

The plant is used in homeopathy[].

The plant is antibiotic against gram-negative and gram-positive bacteria and also pathogenic fungi[, ]. It is experimentally antitumor[].

Agroforestry Uses:

This is a good companion plant for potatoes since it is said to deter potato eelworm[, , ] and the Colorado beetle[]. One plant at each corner of the potato patch is quite sufficient[].
When grown under apple trees it is said to prevent brown rot, powdery mildew and other fungal diseases[].

Other Uses

Horseradish tea is effective against brown rot of apples and other fungal diseases[, ].

Propagation

Seed - this is seldom produced on plants in cultivation[]. If seed is obtained then it is best sown in situ during the spring[].
Division is very easy and can be carried out at almost any time of the year, though it is probably best in spring[]. It s best to use sections of root about 20cm long, which can be planted out into their permanent positions in late winter or early spring, though even very small bits of root will grow away[, ]. Division should be carried out at least once every three years or the crop will deteriorate[].