How to grow Horseradish

Where to plant

Horseradish grows in most soils as long as they drain well and are deep, fertile and rich in organic matter. Loosen the bed 8 to 10 inches deep so the root can grow straight. It grows best in cool weather and needs a fairly cold fall, when the roots size up and develop their bite.

Choose the spot carefully. Every small piece of root left in the ground makes a new plant, so an unmanaged patch spreads. Many gardeners plant it in a buried bottomless pot or a length of wide pipe, or in a bed of its own.

• The Northeast, Midwest, Mid-Atlantic, Northern Plains, Mountain West, Pacific Northwest, Mid-South, Southern Plains and Alaska: plant root cuttings in early spring as soon as the soil can be worked.
• Northern California: plant in late winter or early spring.
• Southern California and Hawaii: it grows in mild winters, but roots stay thinner without cold. Plant in the cooler months, and in Hawaii it is worth trying in cooler upcountry gardens.
• Central and South Florida and the low desert lack the cold winter it needs.

Choosing a variety

Utah State University Extension describes 'Maliner Kren' as the most vigorous variety with the largest roots, 'New Bohemian' as resistant to white rust and mosaic virus, and 'Variegata' as a less invasive variety with cream-variegated leaves. Few garden centers stock roots, so look online or ask a gardener for a piece.

How to plant

1. Use pencil-thick root cuttings, or sets. Cut the top end square and the bottom end at a slant so you know which way up they go.
2. Plant in early spring, about 1 foot apart, with the square end higher, at about a 45 degree angle and 2 to 3 inches deep.
3. Alternatively, split a crown into four pieces each with leaf and root, let the cuts dry for a few days, and plant at an angle with the crown 1 to 2 inches below the surface.
4. Four to six plants are enough for most households.

Watering and feeding

Horseradish is fairly drought tolerant, but roots that dry out too much turn woody and mild, and overwatered roots turn soft. Aim for about 1 to 2 inches of water a week, soaking the soil deeply.

Go easy on nitrogen. Too much gives lush leaves and branched roots. Utah State suggests a teaspoon of nitrogen fertilizer per plant 4 and 8 weeks after planting on top of any fertilizer worked in before planting.

Pruning and care through the year

• Hoe weeds while plants are small; once established, horseradish shades them out.
• Remove leaves that turn brown, and mulch with compost or leaves to hold moisture.
• For smoother, thicker roots, some growers uncover the top of the root in summer and snap off side roots, leaving the main root to grow.

Harvesting

Roots grow most in late summer and early fall, so wait until late October or November, after several frosts, which also improves the flavor. Dig carefully and try to lift every piece, as small roots left behind become weeds. You can also leave some in the ground over winter and dig them in early spring before growth starts.

Trim the leaves to about 1 inch above the crown. Store roots in the dark at 32 to 40°F with high humidity, in the refrigerator or in moist sand in a root cellar; light turns them green. Keep a few side roots to replant next spring.

Growing in pots

A large, deep container or a buried bottomless pot is a good way to keep horseradish from spreading. In Southern California and Hawaii, growing it in a container is the usual advice.