Parsnips

Until potatoes arrived from the New World, parsnips and their carrot relatives were the most important Old World root crops. Besides an important food source, they were also used as a sweetener. Parsnips taste best when exposed to several weeks of cool, frosty weather that converts starches to sugar. Mild microclimates with moderate, not high, summer temperatures produce the most successful crops.

Planting

Grow parsnips from fresh seed; germination is rarely successful with 1-year old seed.
Locate beds in a sunny site and prepare loose, friable, smooth, fine-textured soil up to 1 ft. deep for straight root penetration; clay clods and small rocks can cause forked roots.
Work compost and an all-purpose, balanced fertilizer into the top 6-in. of soil.
Soil temperature should be above 50 degrees for germination, best in May-June. Seeds are very slow to sprout, taking 2-4 weeks. Germination is poor above 80 degrees.
Plant seeds closely ¼-½ in. deep and thin to 3-6 in. in rows 12-18 in. apart. Cover lightly with compost or finely sieved soil to maintain moisture and prevent a crust from forming. In dry or windy weather, cover seeds with spun row cloth or burlap strips and irrigate lightly.
Thin by snipping off seedlings to avoid disturbing the roots of neighboring plants.

Growing Conditions

Water regularly to maintain even moisture; drip irrigation is best.
Spread mulch to control weeds, keep soil cool in summer, and avoid stress from moisture fluctuations that cause poor root formation and quality. Cool-moderate temperatures less than 75 degrees promote best growth. Higher temperatures inhibit growth, quality, and flavor.
Side dress with a light nitrogen-based fertilizer after 1 month then again in another month, working it gently into the soil and watering after each addition.
Mound soil over the tops of roots to prevent greening.
Avoid fungal leaf spot by preventing foliage to remain wet for long periods.
Prevent root rot by eliminating soggy conditions with excellent soil drainage.

Harvesting

Wait for cool conditions after planting, 90-120 days or longer, that last 2 weeks or more before harvesting to allow starches to convert to sugars for best flavor and quality.
Harvest parsnips when roots reach 1 in. in diameter.
Loosen soil with a digging fork before pulling up roots by their tops.
Increase mulch depth with straw, leaf mold, or compost if parsnips are left in the ground over winter. Spring harvested parsnips are considered sweetest and most tender.
Expect roots to become inferior and woody after spring growth pushes up a seed stalk.

Additional Information

Sonoma County Master Gardener Vegetable Planting Summary.
https://sonomamg.ucanr.edu/Food_Gardening_with_Less_Water/

February 2022