In article , June Hughes
writes
Depends where you live. We are in north London and mine is tiny and is
unheated, although when I get round to it, I shall buy a paraffin
heater for it. I usually put down some seeds in boxes in late Feb/March
and cover them with newspaper to germinate, putting a lid on the tray
as well. You could also use fleece, which I find very useful for
protecting seedlings. If you read the instructions on the seed packets
before you buy, you will see that they are generally very clear about
when it is safe to prick out seedlings or put them outside.

Hi June, I also have an unheated greenhouse; it was heated with a brand
new paraffin stove. I put in my tomato plants very early and lost the
lot. One morning the entire glass inside the greenhouse was covered in
black, when I looked in , the plants were covered in soot - it was
evident that there had been an explosion of some kind; what we never
found out, Edward said it was something called a "blowback?? but I have
never risked lighting it again

--
Judith Lea