Posted: 27/05/2015 at 15:59
Its never wise to try grow root veg in pots as they do not like their roots disturbed at all. I grew my parsnips in a similar way to yours last year apart from the sowing of the seed in the pots.
I did the same process of creating a nice deep hole in the ground and filling it with a mix of sieved compost, top soil and mix of high phosphorus feed.
What I did differently then was that I chitted the parsnip seed in a plastic tub on damp blotting paper. When the seed started to germinate I carefully pricked them out with tweezers and sowed them 1cm down in the prepared areas.
I ended up with monster parsnips one that had a diameter of 25cm and a length of just short of 30cm before the thin end of the root.
I also found chitting them resulted in a higher rate of success on the plot as a whole and have done the same this year with approx. 90% success in growth again