Viable parsnip seed question.

To anyone who might have a clue on the subject of the parsnip i left in the ground, with temperatures here going down to minus 25 a couple of times. I did cover most of the row with carpet so i could keep harvesting them and now i am down to maybe 8 left in. At least 2 of these were not covered being at the end of the row and past the reach of carpet. These were the ones i thought to keep as seed plants. My question is; if anyone can tell me if this cold is too much for a seed plant.....maybe i'd be better to keep 2 plants that were covered by the carpet?

Thanks Nobbie. I think what you suggest makes sense. I just hope that the ones i covered will not have been damaged as such for seed production. The ground underneath was never frozen, so i have to admit that the carpet did a mind blowing protection job.