[Kristen]

I've had this before, and not thought too much about it, but this year its just one variety. They have germinated, but the roots seem to be spending too much Time & Effort growing along the soil, rather than into it, and if I remove the plastic-cover I reckon they will dry out

[DD.]

What's on the surface of the trays, Kristen. Looks rather hard & maybe the roots can't get down?

Were the seeds sown on the surface or just below? I take it the ones that have gone downwards were sown in the same manner.

But what do  know about onions from seed? 

[TerryB]

Transplant into modules (40 type ). They should be OK.

[Kristen]

What's on the surface of the trays, Kristen. Looks rather hard & maybe the roots can't get down?

Vermiculite

Were the seeds sown on the surface or just below? I take it the ones that have gone downwards were sown in the same manner.

Seed compost first, gently firmed, seeds pushed just into the compost with rubber-end of a pencil to be level with compost surface, then vermiculite "drizzled" on top. Same for both.

Pretty sure its happened before with Onion seed though - but might have been just this variety last year too.

Last year's were OK when pricked out, its just odd that they have pushed themselves above the vermiculite (during germination I assume) and then grown more root above ground ... and then started growing the green bit.

I'll get on with pricking them out I think