Subject to what you are growing in your greenhouse ventilation is usually quite important in the greenhouse.
For example: A combination of low temperatures, high humidity and poor air circulation, can cause problems under glass.
Here are a few things to consider each of which might make the difference between success and failure with your plants / crops.
Discolouration of leaves may be caused by low night temperatures (red) or fumes from paraffin heaters and poor ventilation (yellow)
Good ventilation is essential, where gas and paraffin heaters are used, as both generate high volumes of water vapour, and traces of toxic gases.
Keep plants on open staging surfaces such as metal mesh or timber slats, to improve air circulation around and through the plants this should reduce possible attacks of grey mould disease (botrytis).
On bright days, temperatures can rise rapidly under glass, so make provision for adequate ventilation.
If you can not be on hand to open and close vents as weather conditions change, fit an automatic vent opener.
Louvered ventilators can prove quite useful as well, as can leaving the door open if security is not a problem.
Some fan greenhouse heaters are fitted with a facility to bypass the heating element and allow the fan to blow out cool air that keeps the air in the greenhouse in motion thus reducing humidity.
Things may be getting quite busy in the greenhouse at this time of the year, not least the need to keep temperatures and humidity in check
Some tasks that might need regular attention are;
The need to open vents early on warm, sunny days, automatic vent openers as mentioned above, will help with this task.
Greenhouse Door Left Open
Damping down the floor will raise humidity and reduce stress to plants through lack of water,as will automatic watering systems and capillary matting.
Creating shade in the greenhouse can be done quite simply by draping agri-fleece on the ceiling and walls of the greehouse, in particular the side that gets most sunshine during the day.
Alternatively you can paint on a water based paste on to the glass, or you could invest in a roller blind will make this chore much easier.
Keep a close watch on minimum night and maximum day temperatures and adjust greenhouse heating and ventilation to avoid drastic fluctuations.
A max/min thermometer is essential to keep an accurate record of temperatures.
There are many forms of thermometers available including digital types with wireless monitors where you can have a unit in the home advising you of what is happening in the greenhouse, thus saving you the need to visit the greenhouse to check conditions.