[Lulu]

I am thinking of planting parsnips in a rectangular planter but they take quite a lot of soil or compost to fill up.  I was thinking of using compost from my garden plastic (darlek type) composter.  Would this be Ok? or would this be too heavy a soil.  What should I mix in with it?  Growing parsnips on the lottie produced parsnips that look like octopussy and they were mostly unusable, which is why I am thinking of doing this.

[Ivor Backache]

They are probably not deep enough. When the seed leaf appears, the root is already about 6-8" long. Start by soaking them in wet kitchen paper . When the roots appear plant in toilet rolls or kitchen paper rolls full of compost. When the leaves appear plant out.  Rarely get divided roots because the young root can grow straight down in the compost.

[Mr Dog]

As I've posted before:
I've successfully grown parsnips in the black 'builders' buckets that you can pick up for £1 or so (up to 8 per bucket, although they obviously don't grow big and are best described as baby veg) and cheap plastic storage crates (they do become brittle after several years outside but as long as you don't bash them they keep going).

I do, however, always chit my seeds these days - I find old seed (3 -4 years old) germinates perfectly well using this method.

[Yorkie]

Compost is unlikely to have sufficient nutrients in it - it's a soil conditioner rather than a compost per se.  They need nutrition all season long.