[DD.]

Covers are fine until the seeds germinate. (I just use re-usable ploythene bags 'cos I'm tight). They help maintain an even temperature and keep the growing medium moist so watering is not so much of a task. Not everyone has a conservatory.

Covers are not fine if you leave them on!

[joyce c]

Joyce, if you read post #3 on this thread there's a link there to chitting sweetcorn 
It's pre-germinating seeds before planting them into compost so that you avoid sowing dud seeds and wasting compost

Many thanks for your info.

[DD.]

I had to sow a few more - thanks to the cats.

I put 72 in to pre-chit & 71 made it!

Only sowed them "properly" yesterday.

[Oliver]

Sorry to hijack, but its related...

my sweetcorn has just started to pop through the compost, not sure exactly when they go outside? and do I need to harden them off??

Always 'harden off' anything that has been nurtured in a sheltered environment before planting it out in the big wide cold windy world. 
And take care of 'tender' plants - don't plant them out before the danger of frost is passed - sweetcorn and beans both get copped by frost.  If you do plant them out, and frost is forecast, cover with fleece or newspaper. Make sure it is secure so it does not blow away!
(But - if the plants are quite advanced when they get frosted, they do sometimes recover, depending how severe the frost was  .......... My neighbour planted his beans  a week ago and they got a bit of frost the following night, but they are still growing well with some scorced lower leaves. Same happened last year).
Oliver