How to Control Humidity in a Greenhouse

Understanding humidity is one of the most important parts of growing in a greenhouse. In this piece, experienced gardener and Master Naturalist Sarah Jay explores the topic and provides 5 ways to control humidity inside your greenhouse.

Close-up of Springer hang watering system in a greenhouse to control greenhouse humidity. There are many different types of lettuce with green and purple leaves growing in the greenhouse.

Contents

Greenhouses give you many options for year-round growing. You can enjoy your favorite warm-weather crops all year with the proper conditions. You can start a propagation operation or grow exotic plants, too.  

Although it may not seem so, a greenhouse can also allow you to grow cold-weather crops in warmer seasons. But there are specific conditions needed to do this.

The basic foundation of what you can grow in your greenhouse relies heavily on how you control temperature and humidity within. You don’t need a professional-level structure to control either condition, but that is an option. Your controls could be as simple as venting the house at the right time. Understanding humidity indoors gives you a good sense of how to adjust it. 

Why Control Humidity?

You want to control humidity in a greenhouse to have the best conditions for plant growth. These are the foundation of successful propagation or simply just good production. 

Plant Preferences

View of a charming vintage greenhouse with various potted succulents and cacti. The greenhouse consists of black metal supports and large glass windows. The greenhouse has a variety of different plant shelves, a wooden table in the center with a central decorative vintage lantern and dog sculpture, surrounded by various potted cacti and succulents.
Humidity controls benefit houseplants by simulating their natural environment.

If you’re growing houseplants, humidity controls are a path to simulating their natural environment. Because so many are from areas of the world with high ambient humidity (above 50%), providing conditions that mimic their habitat helps them thrive. 

The opposite of that is also true. Some plants prefer a dryer environment, and being able to limit the amount of humidity gives desert and prairie plants optimal surroundings. Certain cacti and succulents may have sensitivities to higher humidity levels, for instance.  

Temperature Control

Close-up of a thermometer on a blurred greenhouse background. The round thermometer boasts a compact and classic design, featuring a circular face with a clear, easy-to-read display of temperature readings. The face includes bold numerals or markers against a contrasting white background for quick and straightforward temperature reference.
Adjusting humidity alters temperature; depending on conditions, higher dew points can raise or lower temperatures.

When you adjust the humidity in a space, the temperature is altered. This is a more specific example of how the dew point works in a larger, regional context. Higher dew points or higher moisture concentrations in the air may lead to higher temperatures in certain conditions

However, a higher dew point leads to lower temperatures in shadier areas with good ventilation. Plants that would naturally live on jungle floors come to mind. It’s also perfect for plants that prefer shade and need consistent moisture. A higher ambient humidity promotes a higher dew point, meaning lower temperatures in shaded greenhouses. 

Controlling Pests and Diseases 

Fungus gnats stuck on yellow sticky trap closeup, against a blurred background of potted plants. Non-toxic flypaper for insect pests near Alocasia houseplant.
Maintaining optimal humidity prevents diseases and pests.

Higher humidity levels can lead to higher incidences of diseases and pests. This isn’t always the case, but it’s possible to cause these problems by not paying attention to conditions inside the greenhouse. Especially sensitive plants are prone to fungal and bacterial pathogens that proliferate in high humidity.

The same can be said for pests, such as fungus gnats and broad mites – two of the most common indoor pests. Mosquitos are another example. Low humidity can also provide a habitat for dryness-loving pests like spider mites and mealybugs. Usually, the temperate air in a greenhouse is perfect for all of the above.

Therefore, being able to adjust your controls to ensure there is the least amount of pest and disease infiltration is super important. 

5 Ways To Control Humidity

Here are the ways you can control and augment humidity. There are easy ways to do this; your greenhouse may do exactly what you need to do just by venting it. There are more professional options, and these tend to need less monitoring and intervention

Note that your greenhouse’s structure will determine the effectiveness of your control. If you’re working with a sealed glass structure, you’ll have an easier time than with a plastic-covered hoop house. 

Both are perfectly adequate when they’re properly sealed. You want to ensure the conditions are hermetic so it’s easier to change and adjust when necessary. 

Pebble Trays

Close-up of a tray filled with colorful pebbles filled with water to increase humidity in a greenhouse. Pebbles are oval and round in shape, with different patterns and colors including white, gray, green, orange, black, brown, red and others.
Enhance humidity by placing water-filled pebble trays strategically, but maintain them to avoid issues.

As you would for tropical plants in your house, you can strategically place trays full of pebbles with water in them around your greenhouse to promote humidity. As warmth circulates, it evaporates and hovers in the air, providing more ambient humidity than would be there otherwise. 

You can place a few strategically throughout the growing space and remove them as needed. If you suffer from humidity-related issues, remove them and slowly reintroduce them one at a time. 

One thing to note: these need consistent maintenance. You’ll want to replace the water daily to prevent attracting insects that can damage you or your crops (think gnats and mosquitos). Also, clean them weekly to prevent algae and pathogen build-up. 

Indoor Water Feature

View of a greenhouse full of tropical plants and a lily pad pond in the center. The greenhouse has plants such as Orchids, Sansevieria cylindrica Bojer, Ficus elastica, Philodendron davidsonii, Agave, Vriesea splendens, Monstera, and others. In the center of the greenhouse there is a round-shaped metal above-ground pond filled with water. Water lilies with beautiful pink flowers grow there.
Create a tranquil water feature for ambient moisture, maintaining cleanliness and hygiene.

Make your greenhouse a place of respite with a water feature! This could be something as small as an electrical tabletop fountain or as intricate as an above-ground pond. The splashing and moving water will evaporate into the air and provide some ambient moisture. 

Like pebble trays, you need to keep your pond or fountain clean. Pop in some mosquito dunks or larvae-eating fish to control mosquitos and unwanted insects. If you aren’t using a pump, you’ll also need to ensure algae doesn’t build up in your system. 

Establish a schedule for cleaning to keep things hygienic inside the growing space. You’ll have greater peace of mind that way. If the feature is large enough, you can add plants and fish that will keep the water clean for you. An aquaponic system is not off the table!

Humidifiers and Dehumidifiers

Close-up of a Humidifier in a greenhouse against a blurred background of trays with growing seedlings of various vegetables and plants. The humidifier exhibits a modern and sleek appearance, featuring a compact and cylindrical design. It is made of white BPA-free plastic. The mist outlet, strategically positioned, emits a fine and soothing mist into the air.
Use affordable humidifiers to boost humidity.

There are plenty of cheap humidifiers you can buy and place in your greenhouse. These assist you in controlling and increasing ambient humidity for plants that need it. Greenhouses in dry climates benefit from humidifiers

The inverse can be said of dehumidifiers. They will remove humidity from the air, ensuring plants aren’t overloaded in significantly humid areas. Tropical regions that receive regular rainfall may need a drying source to keep the ambient humidity slightly lower than it would be. 

Some models have a sensor on it that measures the ambient humidity, giving you an indication of how much to increase or decrease your controls. There are even combo humidifiers/dehumidifiers. If you’re unsure where to start, determine the needs of the plants you’re growing and opt for a system that measures humidity. 

Misting System

Close-up of the Misting System against a blurred green background. The Misting System presents a modern and efficient design, composed of a network of slender tubing or pipes strategically positioned to deliver a fine mist. The system features nozzles along the tubing that spray water.
Install a misting system for temperate or tropical plants in hot, dry areas for optimal growth.

A misting system can be a lifesaver, especially if you’re growing temperate weather plants or tropicals in a hot, dry area. The mist makes growing orchids possible, even in the desert. Many expert growers employ mist to keep their plants happy.  

You can DIY one of these with a misting hose strung around the greenhouse’s interior. Attach it to a water spigot, and either choose to turn it on and off as needed or include a timer that will turn it on and off for you. 

Today, sensing technology uses AI to determine what conditions exist in a given growing area. If you want to get even more technical, these are also an option.   

Vents and Fans

View of a small greenhouse with air vents in the garden. The small greenhouse boasts a compact and functional design, constructed with a sturdy frame made of materials like aluminum or galvanized steel. Its transparent walls and roof, composed of durable polycarbonate or glass panels, allow ample sunlight. The inclusion of strategically placed air vents, equipped with adjustable louvers or panels, enhances ventilation to regulate temperature and humidity.
Use vents and fans for humidity control to adjust as needed for air circulation.

Perhaps the simplest way to control humidity is to use vents and fans. While vents are usually included in a greenhouse setup, fans may not be. Therefore, use box fans or small stand fans to keep the air circulating. Fans are great for most greenhouses unless the growing region is already windy. 

Circulating air usually dries the air, reducing humid conditions rather than boosting them. That’s where your vents come in. If you want to increase humidity, close the vents. Keep the fans going to promote air circulation, which prevents diseases and weak-flying insects like gnats and mosquitos. 

Vents and fans also control temperature, just as the rest of the aforementioned methods do. If you notice issues with heat in the middle of summer, open the vents and crank up the fans. Feel free to incorporate other methods to increase humidity if you’d like to. 

Final Thoughts

From simple to more expert-level methods, it’s not hard to control humidity in a greenhouse. There are good reasons for getting a better sense of how to do it, as many humidity controls have a dual purpose. 

Use sensors if you want to, and adjust your humidity levels as minutely as possible!

SHARE THIS POST