I know this sounds daft...

I have an unheated greenhouse.  Will this automatically be frosty if temperatures drop around/below zero? :roll:

You can probably rely on it being a couple of degrees above the outside temp.. If we get a sharp frost it will freeze inside as well.

Good idea to get your hands on some bubble wrap, (often on Freecycle), & double insulate it.

I think a few brave souls also use paraffin heaters during very cool nights.

i have a parasene heater, i thought these were common.  Surely ok as long as you don't leave flammables lying right next to them  :?

Cawdor

I have an unheated greenhouse.  Will this automatically be frosty if temperatures drop around/below zero? :roll:

Yes it will.  I also tried double glazing with bubble wrap and it didn't seem to make a difference.  Your best bet, in my opinion, is to get a heater.

Quote from: "Ice hockey mad[/quote

Yes it will.  I also tried double glazing with bubble wrap and it didn't seem to make a difference.  Your best bet, in my opinion, is to get a heater.

Agree with that Ice i have bubble wrapped mine and accoring to my temp sensor in there it has made very little difference, temp in there is only about 1 deg warmer than outside on a cold night.

Cawdor

I did that too Cawdor, it made very little difference.  I checked the temperature often and realised it was not worth the effort.  Only heating will do the job.  Depending on what you want to grow of course.