How to Cool A Greenhouse?

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A greenhouse is perfect in the winter when you want to continue growing, but in the summer, the trapped heat could be a little too much. It’s important to know how to cool your greenhouse so you can continue producing plenty of beautiful flowers and vegetables.

How to Cool A Greenhouse? There are plenty of ways to cool a greenhouse. The method you use depends on your budget and how much cooling you need to do. Take a look at your options.

  • Plant deciduous trees 
  • Place plants strategically 
  • Use shade cloth
  • Install misters or a fogger
  • Use an evaporative cooler
  • Use a portable air conditioner

Now, that you have your options, you probably want to know how each one works and what it might cost you. I’ve done the research to help you out.

Cooling down the Greenhouse

Before you consider all the cooling options I mentioned, the first thing you need to do is make sure your greenhouse has a ventilation system.

If you’ve read even one greenhouse article, you’ve probably heard that greenhouses need a ventilation system. It’s no joke. Without a ventilation system, your greenhouse will become a hot, steamy, humid mess. Even more than that, your plants will most likely die because a ventilation system provides the carbon dioxide they need to grow.

A ventilation system blows hot air out the roof of your greenhouse and brings cool air in at a lower level. You can choose from two types of ventilation systems: natural or mechanical. Here’s a quick look at the basics of both. 

Natural Ventilation SystemMechanical Ventilation System
Vents on roof and side of greenhouseNo electrical costsMore time commitmentBetter for smaller or larger greenhousesExhaust fan and special opening called louverElectrical costsRuns itselfBest for medium greenhouses

Now, for the rest of the options. The amount of cooling you actually have to do depends on where you live and what you’re growing. I would start with the cooling options that may require a bit of a time investment at first, but then can be left on their own and work for years after.

Plant deciduous trees

Planting deciduous trees is a great place to start for cooling down your greenhouse. Deciduous trees are ones that lose their leaves every fall. 

This means during the warmer spring and summer months, you get a full tree of leaves that provides natural shade over your greenhouse. Those trees lose the leaves in the fall and ta-da, you now have a path for the sun to hit your greenhouse in the cooler fall and winter months.

If you haven’t actually placed your greenhouse yet, search out a spot that already has grown deciduous trees or a spot where you can plant some. Oaks, maples, ash, poplar, and beech trees are all examples of deciduous trees. 

If your greenhouse is already in place, it’s not too late. Go ahead and plant some trees, sooner or later you’ll reap the benefits; in the meantime, though, you’ll need to think about other cooling options.

If you’re starting from scratch, your local nursery would be a good place to start, but you can actually find live tree seedlings on Amazon. Here’s a medium seedling I found there. Check price on Amazon

Place plants strategically 

If you plan your greenhouse just right, you probably already have larger leaved plants in there. If you place these in just the right spot, they’ll help shade the soil and bring the temperature in the greenhouse down. 

The large leaved plants do more than just cool the soil; they act as a natural evaporative cooler. They put off moisture through their large leaves and that helps bring the temp down a few notches. 

Fig trees and grapevines are good options for large leaved plants. Not only do you get the shade and evaporative cooling effect from them, but you get some delicious fruit, too. 

Use Shade Cloth: Shade cloth is a nice, quick, affordable way to create some shade for your plants. You can drape the shade cloth over the top of the greenhouse, pin it up inside near the ceiling or hang it above your plants.

That’s the easy part. The trickier part is figuring out which shade cloth to use. You can find it in all sorts of different materials and colors. Shade cloth is rated by the percentage amount of light it blocks. This is called density and it ranges from 5 to 90 percent density.

The density you need depends on how much coverage your plants need. Here’s a look at what density is best for different types of plants.

PlantRecommended Density
Regular Plants40-60%
Orchids, Ferns75% or higher

Even though shade cloth comes in a variety of materials, they’re not all equal. Darker colors can actually get too hot and increase the temperature. A good material to try is aluminet. Its material allows it to reflect some heat. Here’s one with a 50% density rating on Amazon. Check price on Amazon 

Install misters or a fogger

 A mister or fogger is a good choice for lowering your greenhouse temperature, especially in drier climates. Misters use evaporative cooling to help cool your plants. 

Water is sprayed out of nozzles in tiny droplets. The heat in the greenhouse is used to evaporate the droplets. Since heat is used, it helps lower the temperature. Misters are also a good idea to increase humidity in the greenhouse. You should keep the humidity level between 50 and 70 percent. 

Here’s a misting system on Amazon for just more than 30 bucks. You may need more than one depending on the size of your greenhouse. Check price on Amazon 

A fogger works much the same as a mister except the water droplets are slightly smaller. Check out this one on Amazon. Check price on Amazon 

You can also set your mister or fogger on a timer or humidistat controller, where it clicks on depending on the humidity level. It’s always important to work smarter not harder.

Use an evaporative cooler

An evaporative cooler uses the same concept as a mister and a fogger to cool the air but to an even greater degree. Heat in the air evaporates water and cools things down, sometimes even by 10 to 20 degrees! 

An evaporative cooler uses an overhead water supply as well as a gutter to collect excess water onto a pad. Fans on the opposite wall draw warm air into the pads. The warm air passes through, collects the water and cools the greenhouse. 

An evaporative cooler is a very energy-efficient, cost-effective way to cool your greenhouse.

Here’s one on Amazon that would be useful in a smaller greenhouse. Evaporative Humidifier on Amazon 

Portable Air Conditioner

A portable air conditioner is also a good option to cool your greenhouse. The downside of an air conditioner is that it’s probably your most expensive cooling option. 

The plus of air conditioning units is that many come with a dehumidifier as part of the system. So, while you’re cooling the greenhouse you’re also helping moderate the humidity.

This one on Amazon is an air conditioner/dehumidifier combination. Air conditioner/dehumidifier on Amazon 

Temperature Guidelines for Your Greenhouse

Now, that you know the cooling options you can choose from, you need to know the ideal temperature for your greenhouse.

The best temperature for a greenhouse is 80 degrees, but a lot of that depends on what plants you’re growing. Some plants like cooler temperatures, some plants like warmer temperatures. So, pay attention to temperature guidelines before you crank up the AC and cool your greenhouse down.

Eyerly Family

The Eyerly Family is a family of 8 that loves gardening. Over the past several years we have been applying what we learn about gardening to our own 16x16 raised back yard garden. Our garden is very prolific and we grow a wide variety of vegetables which we love to eat! Click here to learn more about the Eyerly Family.

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