I gave up trying to grow them in my heavy, stony soil years ago and always grow in containers. If you click the link to my blog and scroll down to the entry 'parsnips for dinner' you'll see how I do it.
Jan, as long as they tasted good, it doesn't matter what they looked like
However, this year I simply took my potato planter and removed the soil to the depth of it (approx 12") and filled it with normal compost
I have the straightest hugest Parsnips that every previous
The tops were huge with approx 18" length
I sowed them on my plot with 5 seeds per hole and the holes 6"-8" apart
This was when I thinned them to one, they had nothing to compete for food with and also nothing making them go skew wiff