Armoracia spp.

Southeastern Europe and western Asia

Attracts Pollinators Deer Resistant Drought Tolerant Container Friendly

SunFull Sun – Part Shade

HardinessZones 3–9

Overview

Armoracia spp. is a genus of about three coarse, deep-rooted perennials in the cabbage family. The widely grown A. rusticana, horseradish, forms a clump of large oblong basal leaves 12-24 inches (30-60 cm) long with crinkled, toothed margins on stout petioles, the whole clump reaching 24-48 inches (60-120 cm) tall. Flowering stems rise to 36-60 inches (90-150 cm), bearing branched clusters of small white four-petaled flowers in late spring and summer; many cultivated plants set little or no viable seed. The thick white taproot is pungent, containing sinigrin that releases sharp-smelling allyl isothiocyanate when cut. A. aquatica, lake cress, is an aquatic North American species with finely divided submerged leaves. Roots spread laterally, and fragments left in the soil regrow, so colonies enlarge year to year and can persist after removal. Foliage dies back to the root in winter and reappears in spring. Leaves may be holed by flea beetles and the caterpillars of cabbage-family pests. The mustard oils in root and foliage can cause digestive upset in dogs, cats, and horses.

Native Range

A. rusticana is native to southeastern Europe and western Asia and is now naturalized across temperate Europe, North America, and Asia. A. aquatica is native to eastern and central North America in ponds, slow streams, and marshes. Plants grow in moist, fertile lowland soils and disturbed ground.

Suggested Uses

Grown in kitchen gardens and herb beds as a perennial root crop, spaced 18-24 inches (45-60 cm) apart. The spreading roots suit a confined bed or a buried container that limits lateral growth. Large leaves and tall flower stems also place it at the back of informal borders.

How to Identify

Identified by a basal rosette of large oblong leaves 12-24 inches (30-60 cm) long with wavy, toothed margins and a thick white taproot that smells sharply of mustard oil when scraped. White flowers have four petals in a cross arrangement, about 0.3 inch (8 mm) across, in branched clusters. The aquatic A. aquatica differs in its dissected underwater leaves and smaller stature.

Appearance

Size & Dimensions

Height2' - 4'

Width/Spread2' - 3'

Colors

Flower Colors

white

Foliage Colors

green

Fall Foliage Colors

no change

Bloom Information

Bloom Period

~4 weeks

Spring Summer

White flowers appear from late spring into summer, roughly May through July in temperate zones. In A. rusticana flowering stems are often produced but seed set is sparse or absent. Bloom lasts 3-5 weeks. Cool spring weather lengthens the flowering period.

Detailed Descriptions

Foliage Description

deep green

Growing Conditions

Sun Requirements

SunFull Sun SunPartial Shade

Requires 6-10 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range6.0 - 7.5(Neutral)

357912

Soil Types

loam clay sand

Drainagemoist

Water & Climate

Water Needs

Medium

Frost Tolerance

hardy

Time to Maturity

1-2 years

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Plants grow in full sun to part sun in deep, moist, fertile soil and tolerate a wide pH range. Established roots withstand drought, but leaves wilt and scorch in prolonged dry heat. Root fragments left in the ground regrow, so the clump expands and is difficult to fully remove once established. Flea beetles pit the leaves in spring, and cabbage-family caterpillars chew the foliage in summer. Roots are lifted in autumn after frost, when pungency is highest. Mustard oils in the root and leaves can cause drooling, vomiting, and digestive upset in dogs, cats, and horses.

Pruning

Old flowering stems are cut back after bloom to direct energy to the root. Tattered or frosted leaves are removed in late autumn. Lifting and dividing the crown every 1-2 years limits the spread of the running roots.

Pruning Schedule

summerfall