Parsnips are in the ground for a long time – typically sow in March and harvest from November (they may be ready earlier but they taste better after they’ve been frosted) until February or March the following year.
Soil needs to be conducive to the roots getting down deep, and straight. Lots of stones are bad news – removing them will help.
Germination can be erratic. Fresh seed helps (its one of the few seeds that its probably not worth keeping until next season), and provide them with moisture whilst germinating – water the seed drills daily to keep the top 1/2″ moist.
As an alternative consider Salsify (“A delicate, distinctive flavour likened to Oysters and Asparagus“) or Scorzonera (“Outstanding flavour and held in high regard by French chefs“)- both of which are considered to have better flavour than Parsnips. Scorzonera is pretty scrawny, by comparison, but in my experience germinates very quickly and easily; it is said it helps to repel Carrot Fly, so if that’s true will be a good companion plant in the Umbelliferae / Roots bed.
It is important to weed the bed carefully – the crown of the plant must not be damaged (e.g. by knocking with a hoe!). Water in dry periods, and mulch in Summer.
I have heavy clay, so would probably be better off growing a shorter variety, but we have had success with Tender and True, flavour-wise, so are sticking with that. Perhaps I should grow Gladiator or Avonresister as a test?
Rotation: part of the Umbelliferae / Roots family they normally follow the Brassica / Cabbage family and the plot should not be manured – a plot manured for the previous crop is ideal. Do not fertilize heavily either – it tends to make the roots fork.
Cooking: Dr D. G. Hessayon recommends scrubbing, boiling, and then peeling Salsify and Scorzonera after boiling for better flavour. I don’t think Parsnips are much good boiled, we roast them with the weekend joint.
2009 Season : as an experiment this year I am growing Parsnips (and Salsify and Scorzonera) in pots made from newspaper (See How to make Newspaper pots). This will hopefully enable me to get better germination, and they will be transplanted whole to avoid any root disturbance (and will be planted out very early, almost immediately they have germinated).
One problem I had with this is that some of the seeds I sowed in the paper pots germinated after I planted out the paper pots. I didn’t recheck the plants for additional germination, so I got some “pairs” growing where I thought there would only be one plant.
2009 Varieties: Parsnip Tender and True (grew this in 2008 and flavour was very good); Scorzonera Russian Giant; Salsify Giant.