marigold problem

I've grown some marigolds from last years seed, mainly to put in the GH with the tommys to keep whitefly at bay. Here's the problem. Usually, marigolds come up like lightning, these took ages, and the germination rate was quite poor. Sown in seed trays in the unheated GH, about  a week ago I pricked them out into individual modules and they came on lovely. Now though, at about 1 1/2" tall, one by one, they are looking very poorly indeed. Leaves shrivelling up and starting to keel over. In the past, they have needed very little attention at all, quite tollerant of any sort of conditions. So what could it be? The only thing I can think is it's because I''ve potted them up into last years old tommy compost, but I've done the same with my chrysanth cuttings and other stuff, and they are all fine.

It could be damping off. The humidity has been quite high in there due to the recent weather. I'll get some better ventilation going and stop watering them for a couple of days, as they are supposed to withstand a bit of drought. No Idea exactly what they are. They are from stock that someone gave me last year. They wern't very big plants at their peak last year. You don't think it may be the old compost I planted in?

Here's a piccy I just took. Note that the inner leaves and new shoots at the base of the plant look quite healthy.

I would agree with DBG - looks like damping off - try removing the damaged leaves - they might survive but it is doubtful. Try to ensure that they are kept moist but not soaked and that they have some air. The plants look like they are tagetes rather than calendula. Hope all goes well.   

One by one, they are gradually still keeling over. Even some which were raised in new compost as opposed to the old tommy stuff, so that rules out the compost theory. I've been watering with water from a butt............could it be contaminated water? I'm doing other plants with the same water and they are fine. I reckon I'll give all the watering cans, sprayers and bottles a good fettle. Is it 0k to use household bleach for this if you rinse well?

It's probably a combination of things - too cold, not enough light, poor compost - saved rainwater may contain fungal spores which might have just tipped the balance if everything else was against them, especially if you used too much of it for the speed they were growing at.

Most plants are much more likely to succumb to diseases they might otherwise shrug off if they're not happy, and so far this year many plants are far from delirious! 

And the gardeners ain't very happy either.

Most plants are much more likely to succumb to diseases they might otherwise shrug off if they're not happy, and so far this year many plants are far from delirious! 

Does tha think it'd cheer 'em up if a took 'em art for a pint?

Too risky - they might take a fancy to the barmaid and refuse to come home! 

What!!!! In Barnsley??? Geeor, man. Thar evvin a laugh int tha?