On Tue, 22 Feb 2005 06:45:03 +0000, Alan Gould
wrote:

In article , JB
writes
As we're into late February I started sowing things in the greenhouse
and of course we promptly get a cold snap so I've got out the heaters
to keep everything cosy. Now some of the seed packets I have suggest
that temperatures of 18 - 20 degrees are required which seems
reasonable enough for a day time temperature in a greenhouse at this
time of year but what sort of temperatures can seeds survive over
night and still germinate or for that matter what sort of temperatures
can seedlings survive once they have germinated?

(or putting it another way am I going to have to spend a fortune on
paraffin in the next forthnight?)

18-20 C is about the minimum advisable for seed germination including
overnight. We cover this problem with a propagator set at 20C.
Once germinated, seedlings can survive lower temperatures, but this
present cold snap with February temperatures much lower than January is
causing some difficulties with earlier sown plants. The damage is not
always recognisable at the time, but chilled seedlings can result in
poor plant growth at a later stage.

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).

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?

JB