How to Grow Horseradish

Horseradish (Armoracia rusticana) is a clump-forming perennial plant that's categorized as both a vegetable and an herb. It's primarily grown for its pungent, yellow-white roots that are used to spice up a variety of dishes. The plant features long, shiny, toothed, dark green leaves, and it bears tiny, white, four-petal flowers on panicles in the summer. Horseradish is normally planted in the spring and will quickly grow for the roots to be ready to harvest by fall. Note that horseradish roots are technically toxic both to people and pets.

How to Plant Horseradish

When to Plant

Horseradish is typically planted from small root pieces, also known as sets. Plant them in the fall or early spring as soon as the soil has thawed. The roots need a long growing season to develop. 

Selecting a Planting Site

Pick a sunny garden spot with loose, rich, well-draining soil that's clear of rocks, roots, and other debris. Container growth is also an option, but you'll need a deep, large pot. Note that horseradish can grow vigorously and crowd out nearby plants. So some gardeners plant it in buried containers in the vegetable garden to limit its spread. 

Spacing, Depth, and Support

Root pieces should be planted at a 45-degree angle roughly 3 inches deep. Space them around 18 inches apart. A support structure shouldn’t be necessary.

Horseradish Plant Care

Light

Horseradish plants can tolerate some shade, but their output won't be as good. Ideally they should receive at least six hours of direct sunlight on most days.

Soil

A loose, well-draining soil that's rich in organic matter will produce the best roots. In addition, horseradish likes a slightly acidic to neutral soil pH.

Water

Horseradish has moderate water needs. Too little water can result in woody roots with weak flavor. But too much water can cause soft roots with very strong flavor. Around 1 to 2 inches of water per week is ideal.

Temperature and Humidity

Horseradish likes cool weather. It grows well in temperatures ranging from 45 to 75 degrees Fahrenheit, with prime temperatures being between 60 and 65 degrees Fahrenheit. Humidity typically isn't an issue as long as its soil moisture needs are met and there's good air flow around the plants.

Fertilizer

Fertilize your horseradish at the time of planting and then roughly every four weeks. You can use compost, compost tea, or a commercial 10-10-10 vegetable fertilizer (following the product instructions).

Pollination

Horseradish is pollinated by bees and other pollinators, along with the wind. 

Types of Horseradish

Horseradish varieties are limited. Common horseradish (Armoracia rusticana) might be the only type you will find. There is also Armoracia rusticana 'Variegata', which is more ornamental with marbled leaves. 'Variegata' also tends to be less invasive and more tolerant to shade.

Horseradish vs. Wasabi

Wasabi is known as Japanese horseradish. And in fact horseradish and wasabi plants come from the same family. They both have spicy flavors, though they are distinct. Plus, wasabi leaves aren’t long like horseradish leaves.

Harvesting Horseradish

Fall-planted roots can be harvested in late spring, while spring-planted horseradish roots will be ready to harvest in October or November. Harvest the roots ideally after a few frosts, which improve the flavor, but before the ground freezes. Dig around the base of the plant, and lift the large, central root plus as many of the smaller roots as possible.

Cut down the foliage, leaving only about an inch, and scrub the roots clean of dirt. Let them dry thoroughly. You can keep as much horseradish as you’ll use in about a month in the refrigerator in plastic wrap. Otherwise, store the roots in damp sand or sawdust in a dark root cellar that remains cool but doesn’t freeze. 

How to Grow Horseradish in Pots

If you are worried about horseradish taking over your garden, growing it in a container might be a better option for you. You'll need a sizable container with at least a 30-inch depth for the roots to grow. Drainage holes are a must for the container. And unglazed clay is a recommended material to allow excess soil moisture to escape through its walls. Plant the roots the same as if you were planting them in the ground. Water when the top 1 to 2 inches of soil dries out, and fertilize monthly.

Pruning

As a horseradish plant starts to grow, it will send up multiple shoots. Each shoot is forming small roots and taking energy from the plant. To get one large root like what you would purchase in a store, remove all but one or two of the shoots to allow them to grow larger. The tradeoff of this method is you won't have as many small roots to propagate your plant.

Propagating Horseradish

The most common way to propagate horseradish plants is by saving root cuttings. Not only is this an inexpensive way to create new plants, but it also allows you to make use of excess roots you don’t eat. You’ll save the cuttings when you harvest your horseradish roots in the fall. Here’s how:

1. When digging up the horseradish root harvest, select some side roots that are at least 8 inches long. 
2. Cut them straight across the top and angled at the bottom, so you know which end goes down when it comes time to plant them.
3. Clean the cuttings, and let them dry completely. 
4. Store them in moist sand or sawdust in a cool root cellar, making sure they’re not exposed to light. 
5. Replant them in the spring once the soil is workable.

Another option is simply to leave these side roots in the ground over the winter. However, this can result in aggressive spread in the garden. 

How to Grow Horseradish From Seed

Horseradish is not commonly grown from seeds because the growing season is too short in most areas. It doesn't produce seeds in most regions of the United States. But it is possible to start purchased seeds indoors in January or February and transplant the seedling outdoors in April. Plant seeds about 1/4 to 1/2 inch deep in a moist seed-starting mix. Use biodegradable pots that can be transplanted directly into the ground to avoid disturbing roots. Keep the soil moist but not soggy, and you should see germination in one to two weeks. 

Potting and Repotting Horseradish

Use a loose, organic, quality potting mix for horseradish. One that's labeled for vegetable growth often works well. It's best to plant horseradish in a container that can fit its mature size right from the start, as repotting can disturb its root growth.

Overwintering

If you are growing horseradish as an annual and harvesting all its roots to consume, there's no need to worry about overwintering. But to propagate plants, you can save roots in a root cellar or leave them in the ground. In cold climates, add a thick layer of mulch over the roots to protect them.

Common Pests and Plant Diseases

Few pests bother the roots of horseradish. But there are several that feed on the leaves, including aphids and flea beetles. Aim to plant your horseradish away from other plants in the Brassicaceae family, as they can attract the same pests. Diseases also are rare, but root rot can occur in soggy conditions.