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.
- 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.
- 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.
- 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.
- Sonoma County Master Gardener Vegetable Planting Summary.