Greenhouse Tips for Hot Summer Climates

If you live in a hot summer climate, you may have wondered if a greenhouse would be beneficial. Questions like: 

Would a greenhouse get too hot in Arizona?

How many months of the year could I use the greenhouse?

This article discusses the benefits of having a greenhouse (even in a hot summer climate), the challenges to consider, and the best ways to make the greenhouse a productive space during the year’s hottest months. 

Benefits of having a greenhouse

• Extends the growing season, whether in cold or warmer weather.
• The ability to control the environment, including sunlight, temperature, humidity, and ventilation.
• Protection from the elements.
• Little or no damage from insects, birds, and other animals.
• Increased water efficiency.
• Central location for seed starting and gardening supplies.
• Place to implement hydroponics or other methods.

Challenges with having a greenhouse in Arizona and other hot summer climates 

Historically, the function of a greenhouse is to trap heat. However, during the summer heat, greenhouse temperatures can surpass 150°F (65.6°C), which is too hot for plants. High winds during the monsoon/windy seasons also present a challenge. 

Choosing the best location for your greenhouse

Typically, a greenhouse is placed in an area with the most sunlight. However, in a hot summer climate, taking advantage of locations that offer natural shade is crucial.

Here are a few considerations about where to position your greenhouse:

• Look for locations in your yard that receive shade during the summer naturally. Consider how the sun exposure or shadows will change throughout the year.
• Level ground for the greenhouse foundation. Consider installing a cement pad.
• Protection from the elements. Placement near a house or fence can help. It is also essential to secure or bolt the greenhouse to the foundation. 
• Proper drainage. Ideally, the land surrounding the greenhouse is sloped so that water will drain away from your foundation. 
• Access to electricity and water. Plumb or put these in place before you add a foundation or cement pad. 
• Convenience. Someplace you can access easily.

What to consider before purchasing a greenhouse

Greenhouses come in various shapes, sizes, and use of materials. Available types include traditional, hoop houses, lean-to’s, cold frames, polytunnels, and attached solariums.

Considerations for greenhouses in hot summer climates: 

• Available space. Most people with greenhouses wish they had made them larger. Choose the largest size your space and budget will allow. 
• Design. Do you like the look of it? 
• Cost. What’s your budget?
• Durability. Arizona has severe winds during the monsoon season.
• Material type. A galvanized steel or aluminum frame (for durability) with thick polycarbonate panels (for good light diffusion and insulation) could be an effective solution for a hot summer climate. 
• Height. Adding vertical space can increase the available space for storage and ventilation.  
• Ventilation. Roof vents with (automatic) openers. 
• Misting systems and accessory availability.
• Quality of construction. Insulation of greenhouse with rubber seals, types of windows, etc.

How to keep a greenhouse cool in hot summer climates

Each method will only partially bring down the heat, but combining techniques will bring the temperature down and make the greenhouse usable throughout the year.

• Ceiling fan and circulating fans for air movement.
• Louver (manual and automatic) windows that can be opened or closed depending on temperatures.
• Interior and exterior shade cloth. 
• Tint the windows, just like you would a car. While these other strategies reduce the temperatures by 5-10°F, this method can reduce it by more than 30°F.
• Use a swamp cooler.  

Greenhouse management tips for a hot summer climate

Once you have a greenhouse, a few essential practices will help ensure your greenhouse is a place where plants thrive. 

• Like a garden, plan on spending time in your greenhouse daily to monitor the temperature and plant health. Problems will be easier to manage if you catch them when they are small. 
• Measure the indoor temperature and humidity. Learn which methods for cooling (or heating) the space are most effective. The goal is to maintain the inside temperature between 65-85°F (18-29°C). Try to avoid wide temperature fluctuations. 
• Keep a greenhouse journal: record germination times and temperatures to help you learn from your experiences. 
• Keep it clean. Sweep up or vacuum messes and debris. 
• Don’t overload your greenhouse. Good airflow is crucial for plants.
• Don’t bring pest-damaged or diseased plants into the greenhouse; they may spread those issues to other plants. 
• During the hottest months, you may need to provide additional lighting for plants if the light is blocked by shade cloth.  
• Avoid standing water. Use layers of gym-style pads and rubber mats to drain the moisture out of the building. Water seedlings from the bottom and drain off extra water. 
• Keep the door closed. This helps maintain the temperature and humidity levels and keeps insects out. 

Thank you to Larry Burnett for contributing to this post. 

Larry Burnett is a retired Administrator from Banner Health and a Partner from KPMG. Larry has lived in Arizona since 1984 and gardened here extensively. 

He is a Master Gardener through the University of Arizona and a mentor for Master Gardener students. His favorite time of the day is when he is outside in his greenhouse, garden, and flower beds. Here’s a link to Larry’s Jansen Greenhouse, featured in this article.

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