Why is my greenhouse full of condensation

Why Is My Greenhouse Full of Condensation?

Ever wondered why your greenhouse is regularly full of condensation? Is it bad for your plants? How do I get rid of it? If so, we’ve put together a fantastic guide that will answer all of your questions.

With rare exceptions, condensation problems in a greenhouse are usually more prevalent during the spring and fall months. When there is wetness inside of a greenhouse, dew forms on the leaves of the plants, this is usually a sign that you are not controlling humidity like you should. When it’s sunny outside, like in the summer months, there is an increase in water evaporation from the surface of the soil.

When it’s day time, the warm air will hold any moisture and turn it into vapor.

But as soon as it gets dark and the temperature lowers, that vapor turns to liquid, which is commonly called condensation. This results in water droplets forming on cool surfaces, for example, the leaves of the plants and the window panes themselves.

Humidity levels tend to rise the most in greenhouses in the spring and fall months, and when the cooler temperatures cause condensation, the effect this has on each plant can be quite different. While some plants love the increased moisture in the air, others do not. Some diseases, in fact, are the direct result of too much humidity in your greenhouse, that is, too much condensation. These diseases include powdery mildew and Botrytis blight.

As a general rule, you have to expect that there will be some condensation in your greenhouse since there will always be humidity on its inside, but when the humidity level is too high it can result in fungal and other diseases on the plants. This is where it can get tricky – knowing when the humidity level is just right, too high, or even too low to do your plants any good.

Is Condensation in a Greenhouse Bad?

Condensation on glassCondensation in a greenhouse can indeed be bad, so the trick is learning how to manage the humidity level in your greenhouse so it is just right for the plants you have growing there. When a plant’s leaves get too wet, mildew can form just like it can in your home.

Another reason it can be so bad is that since humidity rises, that excess moisture can hit the ceiling eventually, falling back down in droplets and hitting both infected and non-infected plants and causing the diseases to spread.

In addition, too much humidity can cause even healthy plants not to thrive the way they were meant to, so your plants simply won’t be as healthy as they should be. Let’s face it, you want your plants to grow and thrive, not just get bigger, which means controlling the relative humidity (RH) level inside of your greenhouse is imperative.

The humidity level also affects the transpiration rate of the plants, which is their ability to soak in water and nutrients through the roots and send it through the leaves so the plant will be healthy. Plant tissue can be negatively affected if the transpiration rate either slows down or speeds up, which can happen if relative humidity either lowers or rises too quickly.

How Do I Stop Condensation in a Greenhouse?

Here are some of the ways to reduce greenhouse condensation:

  • Make sure there is adequate air circulation. This is especially important during the fall and spring months. In fact, a ventilation fan is one of the best ways to decrease the moisture content, the temperature, and of course, the humidity level. Just keep in mind that it may take up to 30 minutes for the right exchange of air to occur and to reduce the amount of moist air inside of the greenhouse.
  • Make sure your plants are spaced far enough apart. The right spacing improves air circulation at the plant level. Transpiration always involves an increase in moisture, and that moisture can get trapped if the plants are placed too close together, which results in insufficient air movement and too much moisture.
  • Make sure all of the plants drain well. Greenhouse condensation is directly affected by how well your greenhouse is draining. After all, water that just sits there will increase the humidity level and the amount of warm air in the greenhouse, trapping that condensation instead of getting rid of it.
  • Make sure you water the plants properly. Water them enough so that not too much water falls on the floor, and water them early in the day so that they dry out before it gets dark outside. Too much water contributes to the amount of water in the air, among other things, which causes condensation.

Next, let’s talk about the process of condensation so you can understand why the right humidity levels are so important. In a greenhouse, the relative humidity should be between 50% to 70% at all times. If it gets to the 60% to 80% range, that will work as well, but it should never be below 50% or above 80%.

We’ve mentioned relative humidity, which simply refers to the amount of moisture in the air and which is affected by the temperature, among other things. Warm air always has more moisture than cool or cold air does, and the temperature at which water begins to condense is called the dew point. Sound complicated? It really isn’t.

Think of it this way: if the RH is 95% and the air temperature is 60o Fahrenheit, condensation can form on a plant’s leaf when the leaf’s temperature is only 59o Fahrenheit, so you can see why a little understanding of the weather will help you figure out how to eliminate some of the condensation in your greenhouse.

You likely have thermometers and temperature gauges to give you numbers related to moisture levels in both inside and outside air, relative humidity, and many other important things to know. If the numbers tell you the humidity level in your greenhouse is too high, you can try some of the suggestions above.

Should My Greenhouse Have Condensation?

All plants need some amount of humidity (even cacti to a degree), regardless of what you’re planting there, which means it is not necessarily a bad thing to find a little bit of condensation in your greenhouse. The air temperature, amount of air circulation, and even the moisture in the outside air can all affect the humidity level in your greenhouse.

Since the humidity level affects how much condensation occurs in your greenhouse, the best way to reduce the condensation in the greenhouse is to reduce the humidity level, and this is usually easier than it sounds.

Your greenhouse air has to have the right humidity and temperature levels, and the important thing is to never let your greenhouse get so much moist air that a lot of water droplets form that can fall on the plants and cause them to have poor growth or even disease problems.

Will Condensation Kill the Plants in My Greenhouse?

Condensation on leafCondensation can dramatically increase the odds of you being unsuccessful with your plants. Let’s face it, there are a lot of things to keep track of in your greenhouse, including the temperature, the water levels, the amount of moisture in the air, and even the dew point, but in the end, the humidity, or the amount of moisture in the air of your greenhouse, is one of the most important aspects to control.

It is much easier to do this when it is cold outside, but when it’s cool or warm, it can be a bit of a challenge.

Condensation is worse when the amount of water in the air is too high, and if it stays too high for too long, you can indeed kill your plants because mildew and fungi will get into the plants and cause them to die. 

Fortunately, there are lots of warning signs you’ll notice before it gets to this point, so if you pay constant attention to the moisture of your greenhouse air, it will likely not get this bad.

How to Stop Condensation in a Mini Plastic Greenhouse

The first thing you need to be aware of when you have a mini plastic greenhouse is that a little humidity is usually a good thing because you’re growing seedlings, and seedlings thrive with more moisture in the air. In fact, the temperature and the moisture in the air can both be a little higher in these types of greenhouses than they are in your standard greenhouse.

Much like regular greenhouses, however, they can be too humid, and if they get this way, you can reduce the humidity by following one of these tips:

  • Don’t over-water your plants.
  • Open up the flaps during part of the day to let a little more air in and to reduce the water level in the air.
  • Remember what you’ve learned about dew point, moisture levels in the air, and the indoor and outdoor temperature, and keep track of those numbers in your mini-greenhouse.

Something to Think About

Indeed, many of the same measures you take with a standard greenhouse to reduce the moisture in the air and therefore the condensation level are the exact same. Once the amount of water, the temperature, and the moisture in the air are made lower, the water you see building up on your windows should be greatly reduced.

Let’s face it, this is going to mean much healthier plants and a much healthier and more attractive greenhouse all around.


Remember, a little moisture in your greenhouse is nothing to be alarmed about.

Same with a fairly high temperature because these things help plants, especially seedlings, grow properly and thrive. It’s just when your numbers get too high and you start noticing a lot of water building up on your windows that you need to be concerned, but again, there are simple steps you can take before these things become too much of a problem.

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