In article , JB
writes
Thanks for the useful answer. What happens in the wild then? Does the
soil provide enough insulation to keep daytime and nighttime soil
temperatures much closer than I see in the greenhouse. At present I'm
seeing my greenhouse potting bench swing between 18 degrees in the day
(which seems quite good) and 10 - 12 degrees at night (which seems
quite low and awfully expensive on heating).
In the wild, frost tolerant plants survive much better than less hardy
ones, but it does depend on situation, season, other weather elements
than temperature etc., but there will be many unrecorded losses. Many of
the plants we grow in our gardens originate from wild species, but they
have been adapted for gardening conditions and are inclined to need a
little help.

10-12C overnight should be adequate for average garden seedlings to
survive provided they are kept draught free and the periods at that
temperature not too prolonged.

I have some seedling trays indoors which are racing away but the ones
in the greenhouse seem to still be dormant. If the seeds are chilled
will that matter as much as if the seedlings are chilled?

Ungerminated seeds can tolerate sharp frosts, in fact some require to be
frosted before sowing as part of their life cycle. Once they are
germinated, they become vulnerable.
--
Alan & Joan Gould - North Lincs.