I've done surprisingly well with parsnips for the past 2 or 3 years, first by sowing them into old car tyres filled with the contents of last year's greenhouse grow-bags. Then by sowing them into bits of my giant raised beds that I constructed out of pallets on end part-sunk into the ground to make a 4 foot by 20 foot rectangle, lined with mypex woven plastic sheet, and filled with large quantities of newspapers (about a foot depth - we read a lot of heavyweight newspapers here), then horse poo, then spent grow-bag contents, then B & Q cheap large bales of multi-purpose compost. The aim was to get very fine soil for them to dive down into. It's working well with lots of other things, too - beetroot, spinach, carrots, lettuce, tomatoes, peppers, onions, etc.
It's quite a lot of work, and a bit of expense (especially for the newspapers!), to build these beds, but the aim is to overcome the problems I have in working at ground level - hand-weeding, even cropping - because of chronic problems with back and knee joints. Now I find the cropping much, much easier, beautifully clean, very satisfying.
I've been running two of these large raised beds for 3 or 4 years now, and it's just coming round to time again to clear out the remains of last years crops, and top-up with a bit more horse poo (free), the spent grow-bags from 2 greenhouses (free, now), and some more B & Q multi-purpose compost (bought a few weeks ago, and waiting by the beds - those big bails are heavy to shift, and tricky to load into a car, especially when wet and slippery!)