The harvest period for most vegetables ends with the first hard frost. However, the quality of some root crops, such as parsnips and horseradish, actually improves with exposure to cool temperatures. Parsnips and horseradish should be harvested in late fall or early spring.
Parsnips produce white to cream-colored roots which have a sweet, nut-like flavor. Cool temperatures convert starch to sugar and give the parsnips their distinctive flavor.
Gardeners should be careful when digging parsnips. Damaged or broken roots do not store well. Trim the foliage back to within 1 inch of the roots. Store in a refrigerator or cellar with a temperature of 32 to 40 F and relative humidity of 90 to 95%. If storing in the refrigerator, place the parsnips in perforated plastic bags.
Parsnips can be left in the ground over winter and harvested in the spring. To prevent possible winter injury, cover the parsnips with several inches of straw. The straw can be held in place by covering with a tarp or fencing material and laying concrete blocks or bricks along the edges.
In spring, harvest the parsnips before growth begins. The quality of the crop declines rapidly once growth resumes. (There is no truth to the mistaken belief that parsnips are poisonous once growth begins in the spring.)
The roots of horseradish make their greatest growth in late summer and early fall. To obtain the best crop, delay harvesting horseradish until October or November.
Carefully dig the horseradish and cut off the foliage about 1 inch above the crown. Store horseradish in a refrigerator or root cellar at a temperature of 32 to 40 F and a relative humidity of 90 to 95%. When storing horseradish, keep the roots out of light. Light will turn the roots green.
Horseradish can also be left in the ground and harvested in spring. Harvest horseradish yearly as the roots of old plants become tough and are poor quality.
This article originally appeared in the October 14, 1994 issue, p. 146.