GREENHOUSE VENTILATION

Ventilation in greenhouses is achieved with a combination of roof vents, side vents and the door of course. I believe Air flow is one of the most important aspects to consider when buying a greenhouse.  Low level ventilation can be really essential if you are growing dense foliage plants at ground level, such as tomatoes for example.  Stagnant air in a greenhouse causes such problems as mildew on leaves and fruit.

ADVICE  
Greenhouse manufacturers generally supply the correct number of roof vents with each  model. Remember that the main function of a roof vent is to basically allow the very hot air that rises to the roof space to escape.  Some dealers try to sell you extra roof vents, which must be a way to simply to increase your order value as extra roof vents do not necessarily increase the air flow in an average size greenhouse. 

The most effective way of improving air flow is to ensure you have adequate low level ventilation by adding vents in the sides or ends.  For example a louver at the opposite end to the door will draw air for that end and from the door at the other end, up and out the roof vent(s).  Alternatively position a louver where you intend to grow tomatoes to get air around those dense leaves. Or ideally why not have one at both positions. You can of course  simply rely on your opened door alone but this will only do part of the job.

The other type of side vent offered by some manufactures is the top hinged vent. They are an alternative but my advice is to avoid them. The problem is that when they are open they unfortunately protrude from the natural line of the greenhouse making them dangerous to people walking around the outside. I know, I have the scars to prove it.

Automatic openers are a must for roof ventilators and are available for louvered side vents too.  Auto openers fitted to roof vents overcome the problems of our changeable weather conditions which can often catch you out and ruin all your efforts, particularly in the early Spring months, when an unventilated greenhouse can literally cook young seedlings or make small cuttings wilt.  Go to my page "Important greenhouse Accessories" to learn more about openers.

Beware - there are cheap imported openers on the market which can be unreliable. I recommend roof vent openers by the established UK manufacturer Bayliss, who have a good reliable range at reasonable prices. Please go to "Important greenhouse Accessories"