Horseradish is Best Harvested in Cool Months

Q. I really enjoy the blog. Had a question for you.I planted some horseradish about a month ago. It's growing nicely (I think -- first time I've planted it). But I have five-six nice big leaves coming off the plant.I was wondering when I can tell it's ready for harvest. I've looked online, but most of the instructions involve spring planting and a fall harvest. Since I planted in fall, per the extension service instructions, is there a way to know when they're ready to harvest?

A. Horseradish does quite nicely here for a northern climate perennial but it needs time to develop its roots where we derive the spicy condiment. After the leaves have fully established, it will take two or three months, at a minimum, for harvestable roots (rhizomes).

It is in the mustard family where many members have spicy leaves and stems used in salads. This is perennial mustard so it sprouts from its underground rhizomes each year. The rhizome can be dug in the fall or spring, divided and replanted again to create new plants. 

In colder parts of the United States most planting is done in the spring. But here in the semi-south (actually we are in a ‘Transition Zone’ climatically between north and south), we can plant a lot of things in the fall that are recommended for spring planting in the north.

You could plant during our entire winter if you are careful and have a warm microclimate, or create one, in your garden. Our real “winter” here is the summer months which are more brutal to plants than our winter. 

 If your plant got two or three months of good growth before fall I would've told you to harvest it, divide the rhizome and let it heal and then replant. Now that we are in the second week of November I think it is a little dangerous to recommend that unless you have that warm microclimate I was talking about. 

I would wait until February to mid-March to dig it, divide the rhizome if it needs dividing, let it heal for 48 hours and replant it. If the rhizome has not given you enough growth for it to be divided, then I would just replant it.

 Horseradish is a tough plant. In some parts of the country it is so tough it can be invasive in the garden. Any little section of the rhizome left in the ground after digging can create new plants. So you do not need a big part of that rhizome to start a new one.

There are some critical gardening tips that you need to follow when planting or replanting horseradish or any plant started from rhizomes.

• Make sure the knife you use when dividing the rhizome is clean and sanitized. The cuttings you prepare for replanting can be anywhere from 3 to 6 inches in length.

• Plant the rhizomes horizontally about 2 inches deep and about a foot apart. Don't plant until all fresh cuts, or any damage to the rhizome, has had time to heal. 

• Heal the rhizomes by placing them in a warm spot (warm compared to outside, 60F or so) for 48 hours. This will allow any cuts or damage to begin to suberize or begin the healing process. 

• Be careful not to re-damage the rhizomes when planting. Those parts of the rhizome that recently healed can be damaged easily. 

• Make sure the soil has been prepared with good quality compost to a depth of 18 inches. Horseradish likes composted manure and prefers to be kept moist but not overly wet. It can survive droughty conditions but is not productive.

• It likes surface mulches 2 to 3 inches deep that keeps the soil moist and cool. You should dig them during the cool fall or spring months for harvesting and replanting for best flavor.

Use the large central root for cooking and the smaller, side roots for planting. Horseradish root will go bad very quickly after you start shredding or grating it for cooking. The root oxidizes quickly which ruins the flavor.

Use it as soon as possible after harvest. Shredded or grated horseradish root can be stored in vinegar for short periods of time as this will help keep it from oxidizing. If you are storing it in the refrigerator, keep the roots moist and in long pieces until you need it.

It will probably store in the refrigerator for about 3 to 4 weeks in more humid areas such as the crisper. It can store longer than this but you would need more sophisticated storage than just a refrigerator.