brassica seedlings dying

Hello,

Apologies for the long post, but I want to give you as much info as possible!

Our allotment is heavy clay soil, and last year germination was poor. I was lucky enough to be given a small 6x4 greenhouse for my birthday, and I decided I would try sowing my seeds in plastic module trays (2 inch wide per module) this year.

Whilst its been cold at night, I've had a paraffin heater on at night. However I did not ventilate the greenhouse aswell, and as a result, I believe the brassica seedlings (swede and cabbage) got mildew due to the high humidity (they were fine at first but then went pale, and then died).
Other seedlings (beetroot, sweetcorn, lettuce) were unaffected - though the compost on some of these has turned green (I guess its mold ?), but don't seem to be affecting the seedlings.

I'm now ventilating the green house properly, and have stopped using the paraffin heater.

My question is : Do you think the mildew will still be in the greenhouse, and affect the new brassica seedlings that are starting to come up now ?

Thanks for any help,
Ben

Hi,
Thanks for the reply.

I'd assumed (obviously incorrectly !) that the warmer the seedlings are, the better they would get a start in life.

Outside they go then !

though the compost on some of these has turned green (I guess its mold ?), but don't seem to be affecting the seedlings.

I get that too. On any pots / trays that I sow seeds in I put a shallow layer of vermiculite that cures that.

For things that grow quickly, and thus I can pot on every couple of weeks, I don't bother (once pricked out) as I just cover the green slim with a bit more compost.

But for things that are slower, and stay in their pots for a longer period (usually flowers / perennials that I am growing from seed) I add a layer of vermiculite.