Horseradish
Armoracia rusticana
Pungent perennial root — a clump by the potatoes is said to ward off disease.
- Type
- Vegetable · Perennial
- Botanical family
- Brassica (cabbage family)
- Foliage color
- Green
- Sunlight
- Full sun to part shade
- Watering
- Low–moderate
- Soil
- Deep, rich, moist
- Feeding
- A mulch of compost in spring is all it asks; otherwise it feeds itself.
- USDA zones
- 3a–9b
- Frost tolerant
- Yes
- Flowering
- May
- Plant out
- 14 days before the last spring frost
- First harvest
- 180 days after the last spring frost
- Harvest ends
- 30 days after the first fall frost
- Mar–May Bud Break
- May–Oct Flowering
- Oct–Oct Harvest
- Oct–Nov Growing
- Nov–Dec Leaf Fall
- Jan–Mar Leaf Fall
- Plant spacing
- 19.7 in
- In-row spacing
- 17.7 in
- Between rows
- 2 ft 6 in
- Square-foot density
- Not suited to SFG
- Root system
- A deep taproot
- Working depth
- 24 in–4 ft
- Can reach
- 6.5 ft down where the soil allows
- Spread
- 13–22 in across, about 0.75–1.25× the width of the plant
- Shallowest pot
- 24 in of soil
It mines water and minerals from below anything growing around it, which is what makes it drought-proof and what makes it so hard to be rid of: most of these regrow from any length of root left in the ground.
Every scrap of root left in the ground grows into a new plant, and the fine side roots break off in the digging by design. Grow it in a bin, a bottomless bucket or a corner you have written off, and take the whole plant up each autumn if you want to keep it in one place.
Figures recorded for Horseradish itself. Roots follow the soil either way: a compacted pan, a high water table or heavy clay stops them well short of any of it, and deep open ground lets them go further.
- When
- Dig roots from mid-autumn, after frost has knocked back the foliage, through to early spring before new growth starts — cold weather concentrates the heat. One-year-old roots from a spring planting give the best balance of size and tenderness.
- What to look for
- Foliage collapsed and yellowed by frost, with main roots reaching 2–3 cm thick and 20–30 cm long. Older, multi-year roots grow enormous but woody-cored; annual replanting of side-root cuttings gives cleaner, straighter roots.
- How to harvest
- Dig deep with a spade or fork alongside the crown and lever out the main root, following it down — pieces left behind will regrow (in a confined bed that's your next crop; elsewhere it's an invasion). Trim off side roots 20 cm long and pencil-thick to replant.
- How often
- Harvest as needed through the dormant season, taking whole crowns and replanting cuttings each time. A managed patch harvested annually stays vigorous and contained; an unharvested one gets woody and spreads.
- Storing the crop
- Whole unwashed roots keep 3 months or more in damp sand in a cold cellar, or 4–6 weeks wrapped in a barely damp towel in the fridge. Grate only what you need — pungency fades within hours unless stabilized in vinegar; grated horseradish in vinegar keeps 4–6 weeks refrigerated, and whole roots also freeze and grate well from frozen.
- Cabbage white caterpillars Green or mottled caterpillars of the white butterflies that skeletonize brassica leaves in summer. Net crops with fine mesh before the butterflies lay and pick off caterpillars and yellow eggs.
- Flea beetle Flea beetles nibble the leaves — unsightly, but they do the root no harm
- Spreading well past the patch you meant to give it
Beneficial predators that hunt this plant's pests — grow their favourite flowers nearby to recruit them. companion plant
- Big-eyed bug Geocoris spp.Hunts Flea beetle
A stubby 3 mm bug with enormous wrap-around eyes, working the soil surface and the low foliage for aphids, mites, thrips and insect eggs. It is the main natural check on chinch bugs in a lawn and it is killed outright by insecticide.
- Damsel bug NabidaeHunts Flea beetle
A slender, mantis-armed bug that grabs aphids, small caterpillars, and thrips in low crops and meadowy edges. Leave a strip of unmown grasses and flowers for it to overwinter in.
- Garden birds Passeriformes
Both things are true: birds strip your currants and a brood of blue tits takes several thousand caterpillars out of one fruit tree in a fortnight. Net what you must and welcome them everywhere else — a nest box near the apples is worth more than a spray.
- Parasitic wasps Braconidae & Trichogramma
Tiny, stingless wasps that lay eggs in or on caterpillars, aphids, and moth eggs — the white cocoons riding a hornworm are their calling card, so leave that caterpillar be. Umbel flowers with shallow nectar keep the adults fuelled.
- Spiders AraneaeHunts Flea beetle
Webs, ambushes, and night patrols make spiders the garden’s steadiest generalist predators, taking whatever flies or crawls past. Mulch, ground cover, and undisturbed corners keep the population dense.
Potatoes (deters potato beetles), Rhubarb, Asparagus
Good neighbors
The root has little smell until you cut it — that's when the fiery mustard heat is released.
The Cottage Garden Companion — the gardener's herbarium at cottagegardencompanion.com