You will also find certain areas of the country where the humidity levels are considered too low for plants to thrive in the greenhouse, and for the most part ‘doing’ the opposite of these ideas will help you solve this problem. How to cut the humidity in the greenhouse: One of the best ways to cut humidity or at least minimize the effects of humidity in the greenhouse is to add circulation to the environment. As the humidity rises, open the roof vents, the sidewall vents and add a fan in the greenhouse to help push the air around and up through the vents in the greenhouse. If you have a lean to greenhouse or an attached greenhouse of any type, adding circulation to push the hot air outside will be important. Simply opening the door to the home or garage will not be an answer, as the humidity levels in your house will or in another type of building are most likely similar to that of the greenhouse when the temperatures are hot and high.
Pushing the hot humid air to the outside will cool the interior of the greenhouse most. Pushing air around in the greenhouse will also keep your temperatures more even, mixing the hotter and the cooler air to make the environment more mixed and even. Only use water in the greenhouse when it is really needed. If you set your watering schedule to once every nine days or every eleven days, only water at this point so you will be letting your plants and your greenhouse dry out between waterings. Over watering and using water in the greenhouse when not needed to water the plants will only add additional moisture to the air and in turn will raise the humidity.
If it is watering day, try to water as early in the morning as you can. Watering before the sun comes up will give your plants a better chance to absorb the water before the sun evaporates the water into the air causing higher levels of humidity. Watering your plants in the morning will also decrease the chances that your plants will get ‘burnt’ by the sun burning off the water on their leaves when the sun is full and high. When you keep your humidity levels to a minimum you are also helping to keep certain molds and fungus at bay that thrive on the high humid temperatures of summer. Keeping molds, mildew and fungus to a minimum is much easier when you keep your waterings and your humidity to constant lower level.