Regulating Hot Greenhouse Temperatures

Greenhouse Ventilation

A thermostatically controlled fan can do wonders for pulling cooler air into the greenhouse and warmer air out of the greenhouse.  We used a gable attic fan from a home improvement store, although greenhouse supply houses also offer a wide variety of ventilation systems.

The key points with ventilation are to keep the fan high so it pulls hot air out and place the intake vent low on the opposite wall to pull cool air in.

Greenhouse Shade

In areas where summers are hot, shade is necessary.  It is a simple as securing a shade cloth on the roof of the greenhouse.  There are also different varieties of shade cloths available from the home improvement store purchase to the greenhouse supply house purchase.  Keep in mind that the shade cloth is more effective on top of the greenhouse as opposed to inside it.

I  talked to people that use plants for shade, such as planting deciduous trees around the greenhouse, which shed their leaves in the winter allowing sunlight to reach the greenhouse.  Others use plantings, such as sunflowers along the south wall in the summer.

Greenhouse Humidity

If ventilation and shade are not enough, it is time to add a bit of humidity.  The quickest way to add humidity is spray down the floor.  Gravel floors are ideal as they hold a bit of water and as the water evaporates, it cools the surrounding air.

I added a misting system to our greenhouse.  It is just a simple patio mister set hooked to a time on the water valve.  This has been great as in triple digit desert heat, the greenhouse stays between 85 and 90 degrees!  There are also more sophisticated greenhouse misting systems on the market and even commercial greenhouse fogging systems.  Should you need your greenhouse to be even cooler, an evaporative cooling system is yet another option.

Sometimes the mister nozzles can become clogged with minerals.  To unclog the nozzles, remove the nozzles, soak in vinegar for five minutes, clean with soap and water, then replace the nozzles. 

Before adding any cooling measures, the interior of the greenhouse was over 125 degrees!  My attic fan, shade cloth and misters were an inexpensive way to be able to enjoy the greenhouse all summer long.