Parsnip

Sow fresh seed two to three weeks before your last frost

Work the bed loose 18 to 24 inches deep first, then sow seed a quarter to a half inch deep, two or three seeds per inch, in rows 12 to 18 inches apart. Wait until soil is at least 40 degrees, ideally 55 to 65. Expect 14 to 21 days to germinate, and scatter a few radish seeds in the row to mark it and break the crust. Buy new seed every year. Parsnip seed loses germination and seedling vigor rapidly after one year, so year-old seed is the usual reason a row never comes up. The long taproot forks on any rock or hardpan it meets, and soil above 80 degrees suppresses germination outright, which is why the sowing goes in while the ground is still cold.

Keep moisture even at 1 to 2 inches a week

Give 1 to 2 inches per week depending on weather, and aim for steady moisture rather than a dry spell followed by a soaking. Mulch with organic matter to cool the soil and hold water. Irrigate early in the morning. A swing from dry to wet makes the root take up water faster than its skin can grow, and it splits, cracks and turns bitter. Watering early rather than late lets the foliage dry quickly, which denies Alternaria, Cercospora and Septoria leaf blights the long wet period they need to infect.

Hill the shoulders, then mulch heavily for winter

Pull a few inches of soil over the crowns and shoulders, then after the first fall frosts mulch heavily with straw or compost so you can keep digging through the winter. Grow on raised, well-drained beds if canker has hit you before. Itersonilia canker forms dark sunken lesions right on the crown and shoulder where the root meets the air, and burying that zone in soil physically protects it. The straw layer on top keeps the ground diggable rather than frozen solid, which is what lets a parsnip bed serve as its own winter root cellar.

⚠ Fungicide sprays do not work on parsnip canker. Raised beds, resistant varieties like Gladiator or Andover, covering the crowns, rotation away from the carrot family and clean seed are the only real controls.

Sidedress nitrogen twice, starting six weeks after emergence

Six weeks after the seedlings emerge, band about a quarter cup of 21-0-0 per 10 feet of row alongside the plants, not on them, and water it into the soil. Repeat once more four weeks later. Soil test first and skip this if your nitrogen is already adequate. Parsnip spends a long season building one storage root, and the nitrogen that feeds the canopy through midsummer is what fills that root by fall. Placing it to the side and irrigating it in gets it to the roots without burning the crowns.

Thin to 3 to 6 inches once seedlings are up

After emergence, thin the thickly sown row to leave one plant every 3 to 6 inches. Snip the extras at the soil line rather than pulling them, so you do not disturb the taproots of the keepers. Parsnips are sown thick to overcome their poor, slow germination, but a crowded row yields nothing but thin, twisted roots. Wider spacing also opens the canopy to air movement, which shortens the leaf-wetness periods that leaf blights need to infect.

⚠ Cultivated parsnip carries far fewer furanocoumarins than wild parsnip, but the sap in its leaves and stems is still the same phototoxic chemistry and some people react to it. Wear sleeves and gloves when handling tops on a sunny day, wash exposed skin with soap and water right away, and keep any contacted skin out of sunlight for at least 8 hours.

Scout for rust fly flights and aster leafhopper

Stand yellow sticky traps upright just above the canopy, concentrated along sheltered edges, and count twice weekly to catch the two rust fly flights, one in late spring and one in late summer. Sweep the canopy for aster leafhoppers through midsummer. Keep weedy hosts down around the bed and consider reflective mulch. Aster leafhoppers carry the aster yellows pathogen, and a leafhopper only has to feed for about two hours to pick it up, so the window between arrival and infection is short. Infected plants give you distorted, discolored tops and stunted, hairy, bitter roots that no later care can fix. Traps also tell you when it is safe to take covers off.

Row cover against carrot rust fly, on at sowing

Lay floating row cover over the bed at sowing and seal the edges to the soil. Parsnip is a host for carrot rust fly alongside carrot, celery and parsley, so do not place the bed where any of those grew last year. The adults are weak fliers limited to the carrot family, so rotating to a separate field is genuinely effective. Row covers protect the crop by keeping the egg-laying adults off it, and the same cover excludes aster leafhoppers. The fly's milky-white larvae tunnel through the roots, leaving rusty blotches and forked, fibrous crops. There are two flights to exclude: adults emerge in May and June, and a summer generation flies from August through September. Cover only works on clean ground — the fly overwinters in the soil where its host crop grew, so covering infested ground seals the emerging adults in with your crop instead of out.

⚠ Never cover ground that grew an infested umbellifer crop last season. No insecticide is registered for carrot rust fly in New England, so covers, rotation and clearing all host roots out of the ground before winter are the control, not a spray.

Wait for hard frost, then dig all winter until regrowth

Roots size up 100 to 120 days from sowing, but leave them in the ground until the tops have frozen down and the crop has taken two to four weeks of near-freezing temperatures. Then dig as needed straight through winter and into early spring. Stop the moment new tops or seed stalks begin to grow. Store dug roots unwashed in a perforated plastic bag in the refrigerator produce drawer for 2 to 3 weeks, or hold them in a cool root cellar. Cold makes the plant convert its stored starch to sugar, which is the whole flavor of a parsnip. A parsnip pulled in September is a bland white carrot. In early spring the biennial reverses that trade, spending the sugar to push a flower stalk, and the root loses flavor and goes fibrous as it does.

⚠ You handle a lot of foliage pulling parsnips. Some people report minor skin reactions from contact with parsnip tops: cultivated parsnip carries far fewer furanocoumarins than wild parsnip, but it is the same phototoxic chemistry, so wear gloves and long sleeves, wash exposed skin with soap and water right away, and keep contacted skin out of sunlight for at least 8 hours.