Vegetable · Brassicaceae
Horseradish
Armoracia rusticana
From deep, loose soil rises a thick white root that hands you fiery flesh every fall.
Full sun
Every 7–10 days
140–180 days
USDA 3–9
Overview
Horseradish is grown for the thick, pale taproot that drives straight down under a coarse rosette of leaves. It sits in the mustard family beside cabbage and kale, and the cut flesh gives off the same sharp mustard oils. Left in the ground the root persists as a hardy perennial, its buds pushing up fresh leaves through cold that would kill most garden crops.
The plant grows fast and asks for little. A pale piece of root pressed into good soil in spring throws up leaves and thickens quickly. The real work is not keeping it alive but holding it in place, since the root spreads underground on its own.
Slice into the raw white flesh and it reads as almost nothing, then a sharp heat rises and clears the sinuses. That heat sits locked inside the intact cells until grating or chewing tears them open, which is why freshly grated root bites far harder than anything from a jar.
Care
The short version: full sun and deep, loose, fertile soil, with about an inch of water a week for the smoothest roots. Keep the nitrogen light, snap off the flower stalks, and pen the plant into its own bed so its roots stay put.
Light
Horseradish does best in full sun, which fuels the thickest root growth. It will take some afternoon shade and still produce, though the root comes up milder and slimmer for it.
Water
About 1 inch of water a week swells the root larger and smooths its surface. Once the plant settles in it shrugs off dry spells, but steady moisture is what fills out a good root.
Soil
The taproot drives straightest through deep, loose, fertile loam packed with organic matter. Aim for a pH between 6.0 and 7.5, and break the bed up deep before planting so the root has a clear, open channel down.
Temperature
This is a genuinely cold-hardy plant, its buds surviving winter lows near -31°F (-35°C) and unhurt by frost. It grows through the warm months up to about 86°F (30°C), and a hard fall freeze only sharpens the bite of the flesh.
Humidity
Ordinary outdoor air around 40% to 70% humidity suits it, with nothing to manage. The coarse, tough leaves are far too rugged to mind the moisture in the air.
Feeding
Work a balanced fertilizer or some compost into the bed at planting and that is usually enough. Go light, because too much nitrogen pushes leafy top growth and twists the root into forked, branchy prongs.
Pruning
Snap off the flower stalks as they rise so the plant pours its strength into the root rather than the bloom. In late spring some growers also rub off the pale upper side shoots, a step called suckering that draws the growth into one fat taproot instead of a cluster of thin ones.
Repotting
Horseradish is not a container plant. Grown in a confined bed, its root sets are lifted and replanted fresh each year to keep the crop vigorous and within bounds.
Size & spacing
The leafy rosette rises 24 to 35 inches (60 to 90 cm) tall and spreads 12 to 24 inches (30 to 60 cm) across. Give each plant room and a bed of its own so the broad leaves grow without smothering their neighbors.
When to plant
Horseradish takes its cue from the cold. The pale root sets go into the ground in early spring as soon as it can be worked, the leaves fill out over the season, and the swollen roots come up in late fall after the first frosts, when the flavor bites sharpest.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: Plant root cuttings (sets) at a 45-degree angle in early spring, 4 to 6 weeks before the last frost as soon as soil can be worked.
- Harvest: Harvest roots in late fall after the first frosts; flavor is sharpest after cold weather. Roots can also be dug in early spring before new growth.
Hardiness
USDA hardiness zones: 3–9
Temperature: down to -40°C
Troubleshooting
Horseradish gives little grief, and what does go wrong shows in the shape of the root or in fresh leaves pushing up where they were not planted. Match what you see below and step in early. A little care at planting heads off most of it.
Fresh green blades pushing up from broken root scraps
A pale sliver of root no bigger than a pencil stub will send up a new tuft of leaves, so one dig can seed a spreading stand across the bed. Lifting every scrap of root you can find and stripping off each new flush of leaves slowly drains the buried piece. A barrier sunk into the soil before planting pens those roots in from the outset.
Fix:
- Dig out as much root as possible
- Repeatedly remove regrowth to exhaust the root reserves
- Confine plantings to a contained bed or buried barrier
A taproot that splits into knobs and thin woody prongs
When you lift a root shaped like a gnarled hand instead of one thick spear, the soil was compacted, rocky, or shallow, and the root kinked around each obstruction. Heavy nitrogen bends it the same way, and so does leaving the pale side shoots clustered along the upper root. Loosen the bed deeply, ease off the nitrogen, and strip those side roots once in early summer to draw the growth back into a single straight taproot.
Fix:
- Loosen and deeply till soil before planting
- Remove side shoots from the upper portion of the root in early summer
- Reduce high-nitrogen feeding
Leaf blades punched with pinholes and shallow pits
The scatter of tiny round holes across the green blades comes from flea beetles, while the wider ragged bites belong to cabbageworms and diamondback caterpillars. Draping young plants in floating row cover, plucking off the caterpillars, and dusting on Bt for a heavier wave keeps the foliage intact. The peppered leaves look worse than they are, since the buried root swells on regardless.
Fix:
- Use floating row covers on young plants
- Handpick caterpillars
- Apply Bacillus thuringiensis for caterpillars if needed
Toxicity
People eat the grated white flesh with no trouble at all, and that fierce bite is the whole point of growing it. For animals it is another matter: the same sharp mustard oils locked in the root and leaves irritate the mouth and gut of cats, dogs, horses, and other pets. The plant will not poison them, but a mouthful brings real discomfort, so keep roots and trimmings out of their reach.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds
Safe for
People
Cats Mild
A cat that closes its teeth on the pale, pungent root soon drools, paws at its mouth, and turns from its food. The sharp mustard oils burn across the mouth and leave the stomach unsettled.
Dogs Mild
Dogs are the ones most apt to unearth a firm root and crunch it, and the mustard-oil burn draws out drooling, vomiting, or loose stools. It clears on its own, though a large mouthful is worth a call to the vet.
Horses Mild
Horses seldom mouth the coarse, sharp-tasting leaves, but a single curious bite stings the mouth and gut and can leave a horse off its feed. Keep the plant out of a grazing animal's reach.
Rabbits Mild
The fiery isothiocyanates are far too harsh for a rabbit's tender gut, so even a small nibble of leaf or root brings on an upset. This is not a green to set before them.
Livestock Mild
Cattle, sheep, and goats almost always crop around the peppery foliage, but any that swallow it may show a raw, irritated mouth and stomach. Fence horseradish off from pasture to be safe.
Birds Mild
Backyard poultry tend to pass over the sharp leaves, and a stray peck mostly just irritates the crop and gut. Keep trimmings away from where birds forage.
People Edible root safe
The grated white flesh is a kitchen staple, safe to eat and prized for its fierce bite. The rising fumes sting the eyes and nose as you work, so grate in a ventilated spot and keep it away from your face.
Grating or processing the fresh root releases sharp volatile mustard oils that irritate the eyes, skin, nose, and mouth; work in a ventilated area and avoid touching the face. The plant is not on ASPCA headline toxic lists but is an irritant.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
United Kingdom
Animal PoisonLine: 01202 509000 (fee applies)
Australia
Animal Poisons Helpline: 1300 869 738
Varieties
Only a few horseradish types are grown, told apart mostly by the shape and marking of their leaves. These are the names you will run into.
Common (Bohemian)
Narrow, smooth-edged leaves mark this disease-resistant type, which yields a little less than the broad-leaved kinds.
Maliner Kren (Big Top)
Broad, dark, crinkled leaf blades stand above vigorous, high-quality roots, and it resists disease well.
Variegata
White marbling streaks and mottles the leaves of this variegated type, grown for that foliage rather than the kitchen.
How to propagate
Horseradish never comes from seed. It grows from pale pieces of its own root, each one able to push up a fresh plant, which is part of why a single planting lasts for years.
DivisionEasy
Early spring (or fall lifting for spring planting) · One growing season; roots are usually harvestable the first autumn after spring planting.
Horseradish grows from pieces of its own root, never seed. Cut pencil-thick sets 8 to 14 inches long, then bury them in early spring at a 45-degree angle with the thicker crown end pointing up, or split a growing crown into pieces. Set them in spring and the first firm roots come up that same autumn.
Myths
Horseradish is just a milder relative of the radish.
A shared sharpness is the only thing that ties the two together. Horseradish is a perennial in the mustard family, and its heat forms as isothiocyanates only when the cells are crushed and burst. It is a wholly different plant from the radish.
Once you plant horseradish you can easily pull it out later.
Digging it out is the real struggle. Any pale scrap of root left in the soil pushes up fresh leaves, so the plant roots in and spreads for years. Sink a buried barrier around it if you ever mean to reclaim the bed.