Horseradish

Plant root sets as soon as the soil is workable

Spade or rototill 8 to 10 inches deep and work in well-decayed compost. Set 8 to 10 inch root cuttings a foot apart, angled at about 45 degrees with the fat end up, and cover the top with 2 to 3 inches of soil. Sink a bottomless tub or a 12 inch wide section of PVC around the planting if you do not want it to run. Horseradish makes its root growth in the long cool stretch before summer, so a set that goes in late never sizes up. It also spreads by underground shoots and out-competes almost everything near it, which is why growers confine it from day one rather than fight it later.

⚠ Skip fresh manure. It drives leafy top growth and forks the root into a knot of side branches instead of one straight grating root.

One deep soak a week through the growing season

Give 1 to 2 inches of water once a week, enough to wet the soil 18 to 24 inches down. Water deeply and infrequently rather than in daily sips. The harvestable root sits a foot and a half or more below the surface, and it only chases water that reaches it. Both drought and waterlogging show up directly in the eating quality, turning the root woody or bland.

⚠ Do not overwater. Root rot in horseradish is mostly a wet-soil problem, and it is the disease most likely to cost you the crop.

Side-dress nitrogen twice in the first two months

Work in a complete garden fertilizer such as 10-10-10 at one pound per 100 square feet at planting, then side-dress about a teaspoon of 21-0-0 per plant at 4 weeks and again at 8 weeks after the sets go in. Follow a soil test where you have one. Horseradish is pulling a large leaf canopy and a thick storage root out of the same season, and the nitrogen it needs for that is spent early. Feeding twice in the first two months carries the canopy that fills the root.

⚠ Do not push past these rates. Excess nitrogen makes the plant overgrow on top and branch the root, which is the main quality defect in home-grown horseradish.

Lift and strip the roots twice for one straight root

When the largest leaves reach 8 to 10 inches, ease the soil away from the upper root without pulling the plant, rub off every small side root along the crown and sides of the main root, and cut back to the single best crown of leaves. Firm the soil back and repeat the whole operation about six weeks later. Left alone, every side root and every extra crown becomes its own branch, and you dig a tangled mat instead of a root you can grate. Stripping forces the plant to put the season's growth into one main root.

Save next year's sets and clear every root fragment

As you dig, cut the straight pencil-thick side roots into 8 to 10 inch sets for next spring, bundle them, and bury them in moist sand at 32 to 40 degrees in a root cellar or basement. Chase down and lift every remaining root piece in the bed, and move the planting to fresh ground every three or four years. Any fragment left behind sprouts next spring, which is how a tidy bed becomes a permanent one you cannot dig out. Rotating the site and replanting only clean, disease-free cuttings is the whole defense against the root rots that build up in horseradish ground.

Watch young plants for flea beetles, then mostly let them be

Check new plantings for the shot-hole peppering of horseradish flea beetles and for imported cabbageworm larvae chewing the leaves. Treatment is warranted only on young plants carrying more than about five beetles each, or where 10 to 30 percent of the leaves on seedlings have dropped. Once plants are past the 4 to 5 leaf stage, damage is generally cosmetic and needs nothing. A floating row cover over young plants excludes the beetles without any spray. Horseradish flea beetles feed on the foliage and not on the root you are actually harvesting, and an established plant carries far more leaf than it needs. Spraying a root crop for cosmetic leaf damage buys nothing.

⚠ If pressure on young plants truly crosses the threshold, spinosad and carbaryl are among the active ingredients cleared for garden flea beetles, but confirm the product label lists horseradish and follow its pre-harvest interval before you use it. Pull row covers before any flowering so pollinators can reach the blooms.

Dig after frost has killed the tops

Wait until several frosts have taken the leaves down and the ground is close to freezing, then dig a trench 12 to 24 inches deep along one side of the row and lever the roots out from the opposite side with a spading fork. Expect to need a full 150 day season before the roots are worth digging. Horseradish makes its greatest root growth in late summer and early fall, so every week you wait past Labor Day is adding weight. Frost kills the canopy but the root below is unharmed and at its best flavor.

⚠ Keep dug roots in the dark. Light greens the root and spoils it.