Why Is Your Greenhouse Colder Than the Outside?

As the warm summer months begin to fade away, you may notice that your greenhouse is becoming colder than the outdoor temperature. There are several reasons why this issue may be occurring and, luckily, just as many methods you can use to combat the sudden loss of heat. 

Your greenhouse is colder than the outside because your greenhouse has been unable to warm up during the day. This can be due to a cold spell, bad weather, poor insulation, or lack of sunlight. These factors can contribute to your greenhouse becoming cold despite being warmer outside. 

In the rest of this article, I’ll go over the reasons behind greenhouses losing heat, what temperature your greenhouse should be kept at, how to combat the cold, what temperatures are too cold for your greenhouse plants, and what temperature an unheated greenhouse will keep. Therefore, if you would like to learn more about why your greenhouse feels so cold, keep on reading! 

How Greenhouses Lose Heat

As previously stated, there are a number of reasons why your greenhouse may be colder on the inside. So let’s dive in and look at the most common causes of heat loss in your greenhouse. 

Reasons your greenhouse is colder on the inside:

  • Not enough sun: Greenhouses use the sun to warm themselves and amplify the sun’s rays. If your greenhouse is in the shade or the weather has been cloudy, your greenhouse isn’t getting the chance to warm up during the day and will therefore be colder inside. 
  • Cold weather: Extreme cold temperatures can cause your greenhouse to become freezing and trap that cold inside. Generally, if you are experiencing this problem, using a heater is a great way to remedy the issue. 
  • Wind: Wind can actually leach warmth from your greenhouse as it blows against the structure. This can occur anywhere that isn’t adequately sealed and will result in warm air from the greenhouse escaping. 

The reason this happens is due to the process of conduction. Heat is conducted through the paneling material of your greenhouse in the sun and then converted into energy and warmth; when it’s cold outside, this process becomes more challenging, resulting in a freezing greenhouse.

What Temperature Should a Greenhouse Be Kept At?

Every plant you choose to grow in your greenhouse will have different temperature requirements. However, most plant experts can agree about the parameters on what constitutes a temperature that is too hot or cold for most plants. 

A greenhouse should be kept at about 80°F (27°C) during the summer months and about 70°F (21°C) during the winter months. Typically temperatures below 55°F (13°C) and above 90°F (32°C) will result in death for your greenhouse plants. However, it’s okay if the temperature drops slightly at night. 

As you can see, there is quite a bit of wiggle room temperature-wise to maintain healthy plants. It’s also acceptable for the nightly temperatures to vary so long as they don’t drop into the danger zone of 55°F (13°C) or less. However, you should always do your research on each plant you intend to grow so that you can better meet their temperature needs. 

How To Combat Cold Greenhouse Temperatures

Now that you understand how heat loss in a greenhouse works, the most common causes behind this issue, and what temperatures should be maintained, it’s time to learn what you can do to remedy your cold greenhouse. 

So how can you combat a greenhouse that is colder on the inside?

There are several methods you can try to prevent your greenhouse from becoming colder than the outside. So let’s take a quick look at some of the things you can do to help your greenhouse trap in that much-needed heat. 

Ways to keep the inside of your greenhouse warmer include:

  1. Insulating your greenhouse. Insulating your greenhouse will better trap heat and can be done quite easily. Many opt to use bubble wrap or frost fabric that insulates plants from the cold and is lightweight.
  2. Installing a heater. Using a heater is a great way to control the temperature in your greenhouse, especially during the colder months. This can be done by using compost or a regular propane heater.  
  3. Identifying possible air leaks. Another vital step to keeping heat inside your greenhouse is to ensure the warm air isn’t escaping through small holes or broken window seals. Do your best to inspect your greenhouse and patch up any possible holes through which heat may be escaping. 
  4. Making sure your greenhouse is in the sun. If your greenhouse is placed in partial shade, this may drastically affect the inside temperature. If possible, you should consider moving the structure to a location with more sun. 

Ultimately, insulating and making sure your greenhouse gets enough sun are the best methods to ensure it doesn’t become colder on the inside. If you live somewhere with frequent stormy weather, insulation will be especially important when it comes to maintaining inside your greenhouse. 

How Cold Is Too Cold for a Greenhouse?

Greenhouses’ primary function is to grow healthy plants and extend their growing season. So now that you know how to remedy a freezing greenhouse and the primary causes behind the issue, it’s time to learn about how cold is too cold for your precious plants. 

Anything below 55°F (13°C) is too cold for a greenhouse. Most plants will not survive temperatures below that, and those that do will struggle to grow and produce. However, a cold greenhouse can efficiently be heated using compost or another heating source to keep your soil from freezing. 

If you feel cold when you walk into your greenhouse, chances are it’s far too cold for your plants as well. If your plants are too cold, you will begin to see signs of:

  • Discoloration, especially in the leafy part of the plant.
  • Rotten stems
  • Dropping leaves
  • Curled leaves
  • Bolting

Plants will let you know that they are unhappy with the frigid temperatures quite quickly, and you must act immediately, or else you will more than likely lose your greenhouse plants to frost. The best way to ensure that you are always on top of your game is to purchase and install a greenhouse thermometer. 

A thermometer will better help you to know what temperature your plant nursery is experiencing and how to make changes before the cold becomes fatal for your plants. Unfortunately, cold is one of the most common reasons your greenhouse is killing your plants.

How Much Warmer Is an Unheated Greenhouse Than Outside?

Many people opt for unheated greenhouses as this method is cheaper and, more importantly, who doesn’t love good old solar heating? However, in colder climates, winters might prove to be fatal to your plants. So, how much warmer will your greenhouse be inside without a heater? 

An Unheated Greenhouse is about 5-10° warmer than the outside temperature. However, this difference can decrease due to poor insulation, harsh winter weather, and strong winds. During the summer months, your greenhouse’s temperature should remain steady. 

As previously stated, insulation is vital when it comes to maintaining heat within your greenhouse. A well-insulated greenhouse will do a fantastic job of trapping heat and allowing your plants to turn it into energy. 

Understanding that your greenhouse will only be about 10° warmer than the outside temperature, it’s crucial that you take steps to maintain your greenhouse temp as the weather begins to cool off. If you wish to avoid using a heater, try the compost heating method or wrap your greenhouse in bubble wrap or another insulator. 


Ultimately, there are several reasons why your greenhouse might be colder inside than outside. However, almost all of them have to do with how well your greenhouse is insulated. 

The most common reasons your greenhouse will be colder on the inside include:

  • Lack of sunlight
  • Cold fronts
  • Chilly winds

It’s essential that you insulate your greenhouse well and do your best to patch up any holes where heat might escape. But, of course, you can also always use a heater to combat cold temperatures in your greenhouse.

Alexander Picot

Alexander Picot is the principal creator of TheGrowingLeaf.com, a website dedicated to gardening tips. Inspired by his mother’s love of gardening, Alex has a passion for taking care of plants and turning backyards into feel-good places and loves to share his experience with the rest of the world.

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