Vegetable · Brassicaceae
Horseradish
Armoracia rusticana
Plant it once in deep, loose soil and this tough perennial hands you fiery roots every fall.
Full sun
Every 7–10 days
140–180 days
USDA 3–9
Overview
Horseradish is grown for one thing above all: the pungent root you grate into sauces and dressings. It belongs to the mustard family, alongside cabbage and kale, and it carries the same kind of sharp mustard oils. Left in the ground it comes back year after year as a hardy perennial, shrugging off cold that would kill most garden crops.
The plant is about as easy as gardening gets. Push a piece of root into good soil in spring, give it water and sun, and it grows fast with very little fuss. The real skill is not in keeping it alive but in keeping it where you put it, because horseradish spreads with a will of its own.
Bite into the raw root and you get almost nothing, then a wave of heat that clears the sinuses. That heat sleeps in the cells until you grate or chew the root, which is exactly why a freshly made sauce is so much sharper 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. Skip the heavy nitrogen, pull off the flower stalks, and pen the plant into its own bed so it can't wander.
Light
Horseradish does best in full sun, which drives the strongest root growth. It will take some afternoon shade and still produce, just with a milder, smaller root to show for it.
Water
Give it about 1 inch of water a week and the roots come up larger and smoother. Once it's settled in, the plant handles dry spells well, but steady moisture is what you want if you're after a good crop.
Soil
The root grows straightest in deep, loose, fertile loam with plenty of organic matter. Aim for a pH between 6.0 and 7.5, and till the bed deep before planting so the taproot has a clear run down.
Temperature
This is a genuinely cold-hardy plant, taking winter lows down to about -31°F (-35°C) and shrugging off frost. It grows through the warm months up to roughly 86°F (30°C), and a hard fall freeze only sharpens the flavor.
Humidity
Ordinary outdoor air suits it, somewhere around 40% to 70% humidity, with nothing to manage. Horseradish is far too tough to fuss over the moisture in the air.
Feeding
Work a balanced fertilizer or some compost into the bed at planting and that's usually enough. Go easy here, because too much nitrogen pushes leafy top growth and leaves you with forked, branchy roots.
Pruning
Snap off the flower stalks as they appear so the plant pours its energy into the root instead of blooming. In late spring some growers also rub off the upper side shoots, a trick called suckering that coaxes one fat taproot rather than a cluster of thin ones.
Repotting
Horseradish isn't really a container plant. If you grow it in a confined bed, lift and replant fresh root sets each year to keep the crop vigorous and within bounds.
Size & spacing
Plants reach 24 to 35 inches (60 to 90 cm) tall with a leafy spread of 12 to 24 inches (30 to 60 cm). Give each one room and a bed of its own so it can grow without smothering its neighbors.
When to plant
Horseradish runs on the cold. Plant the root sets in early spring as soon as the ground can be worked, let them bulk up all season, and dig the roots in late fall after the first frosts, when the flavor turns 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 you little grief, and most of what does go wrong shows up in the root or in where the plant decides to grow. Match what you see below and step in early. A bit of attention at planting heads off most of it.
New shoots springing up where you already dug
Horseradish grows back from the smallest scrap of root left behind, so a single harvest can turn into a bed-wide takeover. Dig out every piece you can find, then keep pulling the regrowth until the buried root finally runs out of steam. The surest fix is to grow it inside a buried barrier from the start.
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
Forked or branchy roots instead of one thick taproot
When the soil is compacted, rocky, or shallow, the taproot splits and grows knobby instead of straight. Too much nitrogen does the same, and so does skipping the mid-season chore of rubbing off side shoots. Loosen the bed deeply before planting, ease up on nitrogen, and strip the upper side roots once in early summer.
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
Tiny holes peppering the leaves
Those shot-holes are the work of flea beetles, with cabbageworms and diamondback caterpillars chewing larger patches. Cover young plants with floating row cover, pick off any caterpillars you find, and reach for Bt if they get ahead of you. The good news is the leaves can take a beating without costing you much at the root.
Fix:
- Use floating row covers on young plants
- Handpick caterpillars
- Apply Bacillus thuringiensis for caterpillars if needed
Toxicity
People eat the grated root with no trouble at all, and that's the whole point of growing it. For animals it's a different story: the same sharp mustard oils that give horseradish its kick irritate the mouth and gut of cats, dogs, horses, and other pets. The plant won't poison them, but a mouthful brings on 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 bites the pungent root may drool, paw at its mouth, and go off its food for a while. The sharp mustard oils sting the mouth and can leave the stomach unsettled.
Dogs Mild
Dogs are the most likely to chew a root they dig up, and the burn of the mustard oil usually brings on drooling, vomiting, or loose stools. It passes on its own, though a big mouthful is worth a call to the vet.
Horses Mild
Horses rarely touch the harsh leaves, but a curious bite irritates the mouth and gut and can leave a horse off its feed. Keep the plant out of reach of grazing animals.
Rabbits Mild
The fiery isothiocyanates are far too harsh for a rabbit's sensitive digestion, so even a small nibble can upset its gut. This is not a green to offer them.
Livestock Mild
Cattle, sheep, and goats almost always graze around the peppery foliage, but any that do eat it may show mouth and stomach irritation. Fence horseradish off from pasture to be safe.
Birds Mild
Backyard poultry tend to leave the sharp leaves alone, and a stray peck mostly just irritates the crop and gut. Don't put trimmings where birds forage.
People Edible root safe
The grated root is a kitchen staple, safe to eat and prized for its bite. The fumes can sting the eyes and nose while 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, split between the ones bred for the kitchen and one grown just for its leaves. These are the names you'll run into.
Common (Bohemian)
This is the narrow, smooth-leaved type that shrugs off most disease, though it yields a little less than the broad-leaved kinds.
Maliner Kren (Big Top)
Broad, dark, crinkled leaves sit above vigorous, high-quality roots, and it holds up well against disease.
Variegata
Grown for looks rather than the table, this one carries white-marbled, variegated foliage.
How to propagate
You won't grow horseradish from seed. It multiplies from pieces of its own root, which is part of why a single planting can last 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 root cuttings rather than seed. Take pencil-thick sets 8 to 14 inches long and set them in early spring at a 45-degree angle with the wide crown end up, or simply divide an existing crown. Plant in spring and you can dig your first roots that same autumn.
Myths
Horseradish is just a milder relative of the radish.
The two share a sharp bite and not much else. Horseradish is a perennial in the mustard family, and its heat comes from isothiocyanates released only when the cells are crushed. It is a different plant entirely from the radish.
Once you plant horseradish you can easily pull it out later.
Getting rid of it is the hard part. Any scrap of root left in the ground sprouts again, so the plant digs in and spreads for years. Grow it inside a buried barrier if you ever want the bed back.