[Oliver]

A polytunnel seems to be a double-edged sword.
She has a poly 12ft wide by 15ft long with a window covered with very fine mesh and a roll down polythene flap at one end, and a door with a roll up mesh door and roll up polythese flap at the other.
The temperature fluctuates wildly - hot as blazes in the daytime and pretty cold at night in the early part of the season, then hotter than blazes in the daytime and somewhat cooler at night in the summer.
So he opens the door and window in April and May, when things are hatching, to allow ventillation and he closes them up at night.
From mid May they leave the door open unless it appears it will be really cold, possibly frosty, then the window is closed up too.
Plants are taken out of the poly every morning to 'harden off', but tomatoes, cucumbers, melons, peppers and cape goosberries are grown in the tunnel and stay there all the time. When danger of frost has passed plants stay outside until they are all planted out on the plot.
From June onwards the door and window are left open all the time with the mesh in place to stop bees and butterflies from committing suicide by getting stuck inside. they die pretty quickly if they get caught between the shading and the roof of the tunnel - its very hot there. If she is working in the tunnel then the mesh door is left up to increase ventillation because she can keep an eye on the bees and butterflies and evict them.
Not much is kept in the poly over winter unless it is covered with fleece as the temperature in there is the same as outside - Cold.
Could line the poly with bubblewrap I suppose, to keep the temperature up a bit, but not got that far yet!
If anyone has any advice she would be delighted to learn. Regards Oliver.

[GrannieAnnie]

This is my first year wiith a polytunnel Oliver, no no words of wisdom from me, but I am hoping it will stay warmer than outside for a bit longer so I can extend my growing season.  I have got a 2nd hand gas heater for it, as long as I can afford to buy the gas!!!!  It will be interesting to see what happens, but you are right about the temperatures.  It is usually over 40 C in there during the day!!!

[Oliver]

heat!

She doesn't heat the poly at all  doesn't believe in heating the neighbourhood!
The sweet peas like it in the poly - cold, but protected from the wind. (Sow the sweetpeas in September and keep them well watered until planting out in March. they can also go in a coldframe.)
and in January the Lobelia also like it under their fleece. They still need water from time to time.
For the rest of the winter (from about December) she just puts stuff she wants to keep low down on bubblewrap and covers it with fleece and hopes for the best. Some things have pegged it  sometimes - tradescantia and streptocarpus and others - lettuces - have been ok.
Come March, however, and away we go!