Horseradish (Armoracia rusticana) is a member of the Brassica family grown primarily for its root, which is ground into the popular condiment. The whole plant is edible though. The leaves are an early and nutritious green, sort of like kale, eaten raw when they are small and tender, and wilted or boiled when they grow larger. The vitamin C content of 100 grams of horseradish leaves can be 5 times the US RDA or more (as much as 3500mg/kg) and they contain a large amount of sinigrin, a compound with anticarcinogenic properties. The leaves are a little more bitter than Brussels sprouts, but have a similar flavor overall. Younger roots can also be cooked and eaten, although they get tough and fibrous as they mature. Although I like horseradish sauce, the amount that I use in a year would hardly justify growing a single plant. Instead, the greens are my main breeding interest with horseradish. There is great value in a perennial plant that can survive for 20 years or more and produce a crop of early greens each year. When your kale seeds are just thinking about germinating, horseradish greens can be ready to harvest. Added to that, horseradish is much more cold hardy than any of the various perennial kales and cabbages that can barely survive where winters dip below freezing.
This is the common heirloom variety, which is to say, probably the same horseradish that you can buy from a great many seed suppliers, offered without a varietal name. Professional growers would identify this as a “type 3” horseradish. There are quite a few horseradish varieties, but most are only grown for commercial production and lack traits that would make them of any greater interest for garden use. Common horseradish is widespread and is probably the main horseradish that has been sold for garden use in the USA. There isn’t a lot of difference between one horseradish variety and another, but common horseradish is vulnerable to Turnip Mosaic Virus, while modern varieties bred for commercial production usually are not.
Horseradish “thongs” or “sets” are short sections of root. Ours are at least four inches long and 1/3 inch diameter. Whenever the soil is workable, plant them vertically one to two inches deep with the thicker cut end closest to the surface of the soil and you’ll have new plants in the spring. Don’t harvest leaves the first year. Give the plants a full growing season to get established.
Horseradish can be invasive, so be careful where you put it. Even small bits of root have the ability to sprout and start a new plant. I have heard plenty of tales of people who accidentally ran a tiller through a horseradish plant and ended up with a lot more horseradish that they ever wanted. If you just want a few plants to make your own horseradish sauce, this would be a great plant to grow in pots.