Sowing: Sow parsnip seeds in spring for autumn harvest; sow seed 2-4 weeks before the last expected frost to 4 weeks after the last frost. In mild-winter regions sow in early summer for winter harvest or in autumn for a spring harvest. Sow seeds ¼-½” (6-13 mm) deep. Parsnips can be slow to germinate—from 5-28 days; about 21 days at 60°F (16°C). To improve germination, soak seed in water for a day before planting. Grow parsnips in compost-rich soil stones free to a depth of 18” (45 cm). Grow parsnips in full sun to partial shade.
Growing: Thin successful plants to 3-4” (7.5-10 cm) apart in all directions. Keep the soil evenly moist during the early stages of root growth to prevent the roots from splitting. Carefully work well-rotted compost or manure around plants 4-6 weeks after seedlings emerge. Side-dress plants with fish emulsion once a month during the growing season. In severe winter climates protect unharvested roots from freezing over the winter with 6-10 inches (15-25 cm) of straw.
Harvesting: Parsnips will be ready for harvest 95-100 days after sowing. The sweetest roots are lifted after heavy frosts in late autumn. Complete your harvest by early spring before top growth begins again. Roots left in the ground all winter will have the best flavor, sugar content increases with cold weather. Do not leave roots in the ground a second season as they will become too fibrous to eat. Parsnips will keep in the refrigerator for 2-4 months in perforated bags or bins.
Read more detailed parsnip growing articles at Parsnips.