germination/vermiculite problems

This year I used perlite to top my seeds with and they've been great, with no sign of mold at all. Vermiculite would be very similar.

The usual cause of problems with mold is overhead watering and watering too often. The potting mix (I assume its mix and not true soil) needs one good soaking from below to get things rolling, then it's usually okay for a few weeks. Keeping the dome on isn't such a great idea with vermiculite/perlite as they already help keep in moisture and I found them great for preventing damp off (the mold problem) from starting. But I left mine only lightly covered, mostly to keep the cat from using the 'new' litter box or snacking on seedlings.

Thyme is a dry/arid plant and needs very little water and no dome at all. cosmos can be slow, same with verbena. Be patient and give them more air. Touch a finger to the potting mix and if it's still dampish, don't water for a while yet.

I won't put them on the compost heap just yet then,take off the domes and hope for the best

I know the feeling Gallen it seems sometimes that it doesn't matter how careful you are nature likes to let you know whose boss now and again.I think the most important thing is to concentrate on the positives and put the negatives down to experiance(and learn from them if at all possible