it looks like loo roll holders and paper pots are a no no as I said recycle recycle there in the bin so back to growing parsnips and I take your point sowing in the grounds a better idea maybe best to direct sow April ?
I think I'm going with the idea of making a hole around 30cm filling with compost 2 seeds per station the only problem is weeds usually grow faster than the parsnip seed maybe leave a wider space between the rows and plants ?
I make a drill, water it heavily, then once the water has drained sow the seeds. Then I cover the drill with bagged compost, and stand on it to press the compost down. I don't water after that, although if its really dry then I would not much of an issue jn glasgow! so it has no weeds along the drill. I do the same with carrots. It doesn't use up too much compost and makes it easier to do any weeding come thinning time . They grow nice and straight when sown onto firm soil I find. These are typical from last year