In message , eptal
writes

Hi, this is my first post to this site, so I hope you will forgive me
if
this problem has been covered before. Every year the overwintering
plants in my unheated greenhouse suffer from grey mould.

This tends to be a problem with UK winters. Cold grey foggy days are
perfect for fungal spores to germinate and dormant plants are
vulnerable. You may find some species fail more easily than others -
frost will seriously affect most tender plants in a greenhouse so if you
can keep it frost free that will help a lot. So will ventilating on any
"warm" sunny days.

I make sure
that the plants are not too close together and that the greenhouse is
well ventilated, although up here in Morayshire most of the air going
in is fairly damp. I wondered if there was a spray someone could
recommend that might prevent this, as I am a bit wary about using
sprays on dormant plants.

There used to be a smoke that you could use, but it was withdrawn some
while ago because it was effective (ie also dangerous)

I tried green sulphur powder last year but
it did not have much effect.

It wouldn't.

Regards,
--
Martin Brown