Greenhouse ventilation

InTheMoorlands

I've a small heated greenhouse with a few veg. and bonsai plants taken inside for the winter.  Due to the weather it's been shut up quite tightly over the past week or so.  I always keep the greenhouse well ventilated in summer but just wondered about winter.  When its not freezing should I open a window or would the plants be happier being kept a bit warmer with everything shut up. 

I recall reading an article about the importance of greenhouse ventilation but can't find it now.

Paul B3

My own moderate sized g/house is unheated ; I overwinter several acclimatised & hardy cactus plants , large Aloes plus several borderline hardy shrubs and tender perennials .

I believe that good ventilation is important to 'toughen' up the plants , so on mild and frost-free days I open doors and windows .

Even though most of the plants are completely dry , in my opinion premature growth can be initiated too early in the year , only to be caught out by Spring frosts . Under glass on a sunny Winter day the temperatures can become fairly warm if only for the short term .

To summarise ; let the air in ! 

punkdoc

I open my cold g/h containing seedlings, borderline hardies etc almost everyday, I believe it helps to stop it getting too damp, which rots the plants.

borgadr

I open mine whenever it's above about 8 degrees or so, like it has been the last couple of days.  I think the extra air circulation is much more beneficial than a few extra degrees when the light is so low anyway.

bédé

A big no, no, is humidity in cold weather.  

I open my greenhouse door every day; the vents are always left slightly open.  Of course on really inaccesible days I may leave it. 

You can do your own test by visiting your greenhouse after about 1 hour of full sun.  A max-min thermometer is essential, summer and winter.

InTheMoorlands

Thanks everyone, it's much clearer now.  I wasn't sure that the benefits of higher temperature would outweigh coldish fresh air.

I'll just need to watch the temperature as we are almost 750 feet up and it can get quite cold very quickly.  I've a maxi-minimum thermometer which I keep a careful eye on.  Last week it register 0.5C even with two small heaters in the greenhouse.  The outside thermometer measures -20C but I don't think its working properly, although it is in a cold part of the garden.