[Yana]

Ive just read the Allotment Newsletter for July 2012 and it mentions the issue of mildew in the greenhouse.
There in lies the conundrum...... the greenhouse needs to be kept warm so the automatic vents do not open because the temperature is not high enough ...... because the vents do not open, condensation builds up ......
I have made a 'false door' for each of my two greenhouses and covered with wire netting to use when the temperature gets too high in the greenhouse so I can slide the glazed door open and the 'false door' closes over the gap.
Should i be using this door now to ensure good air flow (temperature will drop) or reset ths automatic vents to open at a lower temperature?

[JayG]

Weather conditions are making it very difficult to find the right balance, exactly for the reasons you describe.

My greenhouse is misted up every morning but with slightly warmer temperatures and the occasionaly glimpse of sunshine the autovent usually opens just enough to let the condensation out with the door completely shut.

On really dull wet days it struggles to open even that much, but I doubt whether opening the door would make much difference in such conditions.

I seem to be just about getting away with it at the moment, although there is a lot of finger-crossing going on because although still healthy all the stuff in there needs more sunshine (don't we all?!) 

[mumofstig]

Unless the forecast is for temps under about 12C at night I'm leaving the greenhouse door open a couple of inches..........I've had everything spoiled by botrytis in the past and don't want it happening again

[compostqueen]

my unheated greenhouse doors and windows have been open since April.  I have peppers and aubs in there, and apart from a bit of silvered leaf on the aub as I left it near the open door, things are fine.

You can buy those cheapo solar fans from e bay which you can clip on at various places in the greenhouse if you want more air movement but if both doors are open you should get enough draught blowing through. 

[Kleftiwallah]

When I constructed the base to my large greenhouse (actually two fish plated together),  I built a low wall of bricks (with holes in) and the holes were horizontal to allow adequate ventilation. 

I've had no problems with condensation and the windows are rarely opened.  Cheers,    Tony.

[Yana]

Thanks all.
Seems to be a combination of checking the night time temps and keeping an eye out.