I am also slightly confused, sorry to add. Is my polytunnel equivilant to a normal green house eg I can plant out early may, if I cover with fleece on cold night?
What I have gathered from the posts above and some further research is that basically outdoor, polytunnel or greenhouse, the minimum nighttime temperature should not be below 10C. if it is it can stunt growth completely or slow it down, and when in flower can affect the pollen (I have 2 plants in flower now!). I have read that it can cause 'unexpected tomatoes' ie too small, more prone to splitting etc though I'm unclear if this just affects the trusses that have developed when it is cold, or all (I assume the former).
I believe one advantage of the greenhouse or polytunnel is that plants are less affected by the wind which I believe can also be a large factor \ benefit compared to plants in the ground outside.
With all that said, I've no idea how you plant without a heated greenhouse assuming earliest nighttime temps consistently 10C will be sometime in June.
I'm going to have to try a few sacrifical ones and see what happens - next year I think actually I'll hold back
- mine were planted late Feb and then again early April but both seem early based on the above - the feb ones I knew were in fairness and I was warned!
My major issue now is that I have to trade off more sun + cold nights vs less sun and warmer nights - I'm not sure what is best out of those, though I guess it seems fairly conclusive that cold nights are not good.
Good luck and I hope that helps!!
Al