Growing Horseradish

Horseradish (Armoracia rusticana) is in the brassica family, which includes turnips, kale, mustard greens, broccoli rabe, daikon radish and many other plants with varying degrees of pungency and a similar taste. Native to the temperate regions of Europe and Asia, this an ancient herb grown for its pungent roots and is a very easy-to-grow perennial.

Even though you dig up the plant to harvest the roots each year, new plants can (and will) return in the spring from any small pieces of root still in the ground. It is so prolific, it can get out of control if you are not careful, a good reason to grow it in pots!

Though horseradish is used sparingly due to its strong hot flavor, it does add some nutritional benefits to your food. Lots of vitamin C, potassium, calcium and magnesium to name a few. When ground, the root produces isothiocyanates, chemical compounds that are studied for their anti-cancer properties.

It's leaves are fabulous as peppery salad greens too, but the true value of this plant is in the wonderful horseradish root sauce that you can produce. The roots are chopped, grated or minced, and usually mixed with vinegar, bottled and then used as a condiment. The stuff you buy in the store doesn't even compare! Makes the best horseradish crusted salmon!

How to get started

For best results start with a selection of root cuttings from a reputable grower, or from a garden centre or gardening catalogue. Organic gardeners all over the world will share horseradish roots to get people started. If you know anyone with a horseradish plant already, these can be great sources for your 'starter' root. 

When to plant horseradish

If you are going to grow your horseradish in the garden rather than a pot, choose a sunny location and allow for at least 18 to 20 inches between plants. They will get to around 3 feet in height as well. With very large leaves, which can shade out most other plants grown nearby. Thankfully, they also shade out most of the weeds.

Planting should be done as soon as your ground is thawed enough to dig. You’ll want to dig down at least twice as deep as your piece of horseradish root is long to provide loose soil for the long taproot.

Purchased roots for starting horseradish usually have a square cut at the bottom and a slanted cut at the top, so you can tell which way is up. Bury the root standing “upright” with the slanted cut at the top, just above the soil level. If you buy a root without any clear top to it, you’re better off planting the root horizontally just a few inches under the soil and let the plant figure it out.

Keep the soil moist until you start to see sprouts coming up. Continue regular watering to keep the soil moist until the plant has developed several sets of leaves. Then it should be fine with just rainfall on its own.

Though horseradish will thrive even when neglected, you can help your plants out with a mid-summer application of a low-nitrogen fertilizer. A standard formula will promote too much leaf growth at the expense of the roots.

While the plants are growing, you can actually pick a few of the young leaves and add them to salads. They can be kind of spicy, so only try a few. Later in the season, your plants may go to flower. Horseradish blooms are small, white and not particularly showy. They won’t harm your future root harvest so don’t feel you have to cut them off like with many other herbs.

Horseradish is in the same family as broccoli and cabbage, so be prepared for the same host of insect pests as you find with these other vegetables. In particular, keep an eye out for cabbage worms. They are the larvae of a white butterfly that will lay its eggs on the leaves. They prefer cabbage but will be happy to feast on your horseradish if it’s nearby. Look for slim green caterpillars, and pick them off immediately.

Because horseradish can spread mercilessly through your garden, many people prefer to grow it in containers. You will need a very large pot to allow your plant to really thrive. A 20 gallon pot, or even a half-barrel is the best. Make sure there is good drainage and plenty of holes in the bottom.

Harvesting horseradish

You can either harvest your horseradish in the autumn after the first hard frost has killed back the top portions of the plant, or in the early spring just before new sprouts form. The root flavor intensifies quite a bit after a frost but if you prefer milder horseradish, then harvest a bit earlier.

Gently dig up your plants and cut away all the thick roots. To start new plants for the next year, leave one or two pieces in the soil. This will work fine to start new plants even if you are harvesting in the fall.

Quite often, you will have new plants spring up even if you don’t intend it. If you really don’t want any more horseradish plants, you will have to thoroughly dig the soil to remove all the pieces of roots.

Preparing horseradish

Once you grate horseradish root, it will soon start to turn dark unless you mix with vinegar. Once vinegar is added (usually referred to as prepared horseradish at this point), you can store it in the fridge for 6 weeks.

When you grate your horseradish, do it somewhere well-ventilated. The fumes are very potent can will burn your eyes and nose. Best to keep a window open if you can.

For later use, you can store the whole roots for about 3 months in a container with damp sand. It’s not really the most practical method but horseradish needs to be kept moist. Or you can freeze it once grated. The whole root doesn’t freeze well.

The longer you store your horseradish roots, the less flavorful they will be. That goes for prepared horseradish as well.

Further reading