How to Grow Parsnips in the USA

Quick Facts

Factor	Value
Soil pH	6 - 6.8
Germination temp	54°F (12°C)
Optimal growing temp	59-70°F (15-21°C)
Minimum survivable temp	23°F (-5°C)
Time to harvest	100-120 days
Soil texture	RHS: "deep, light soil that drains readily"; avoid "stony or compacted soil", which causes forked roots.
Drainage	RHS: soil that "drains readily", in an "open, sunny area". Utah State: "sunny locations".
Edible parts	roots

At a Glance

Spring Sowing -- and Is Fall an Option?

Illinois Extension: "Plant seed in early April or May in deep, fertile soil that is well prepared." That's the one universally-confirmed window across the US -- seed is slow and erratic to germinate (14 to 30 days is normal), so a patchy-looking row in week two isn't a failed sowing.

In most of the US, spring is the only real sowing window -- parsnip needs 100-120 days plus a spell of near-freezing weather afterward to sweeten, which a fall sowing won't get before hard frost outside mild-winter regions. If you're in coastal or inland Southern California, it's worth trying a fall sowing instead, roughly September through the winter -- UC Cooperative Extension there sows other cool-season roots like carrots and beets on that same window, though their guide doesn't give parsnip its own date, so treat this as a reasonable bet borrowed from its garden neighbours, not a confirmed figure.

Growth Stages

Stage	BBCH	Notes
Sowing & germination	0	Make a shallow 1cm-deep drill, sow thinly or three seeds at 15cm intervals, rows 30cm apart. Notoriously slow and erratic to germinate, needing soil around 54°F (12°C) -- a mid-spring sowing succeeds far more reliably than an early-spring one on cold ground. RHS.
Thinning	3	Thin to one seedling every 15cm, removing the smaller, weaker ones. RHS.
Root development	4	The long, tapering root develops through summer and into autumn -- a slow-growing crop that spends the whole season bulking up rather than maturing quickly. RHS.
Harvest (after frost)	8	Best left until after the first heavy frost, which intensifies sweetness and flavour by converting starches to sugars. Ease roots out intact with a fork; they can be left in the ground through winter and lifted as needed. RHS.

Soil & Growing Conditions

Water: RHS: water "during dry spells" and keep the soil "evenly moist" to prevent root splitting. Utah State: "1-2 inches per week depending on weather", applied "frequent and uniform".

Soil pH range

6 6.8

Span reflects genuine variation between the cited authorities, not a single agreed figure.

Harvest & Storage

When to pick: RHS: lift once "leaves start to die down in late summer or autumn", and flavour improves "after the first heavy frost". Utah State: harvest "when the roots reach full size".

Storage

RHS: parsnips "can be left in the ground into winter and harvested as required". Utah State: store at "32ºF and 95% relative humidity for two to four weeks".

Diseases

Downy mildew (general)

RHS names parsnips among the vegetables affected by downy mildews.

Pests

Stem and bulb nematode

Ditylenchus dipsaci

RHS names parsnips among affected vegetables, showing "crown and leaf base swelling, rotting, and splitting".

Carrot fly

Psila rosae

RHS: carrot fly affects "Carrot, parsnip, parsley, celeriac and celery".

Sources

1. Utah State University Extension - How to Grow Parsnips in Your Garden

These source is specific to this region. The full list of 6 sources behind this guide (FAO EcoCrop, Royal Horticultural Society, Utah State University Extension) is in the references of our UK guide to parsnips; they describe the plant itself, which is the same wherever it grows.