How to Use a Hygrometer in Your Greenhouse

June 20, 2025

Humidity is more often than not overlooked in gardening and greenhouse growing. Too much humidity, and you're inviting mold in. Too little, and your crops end up drying out. Placing a hygrometer in the greenhouse allows you to stay in control and monitor humidity levels. Let's explore how to choose, set up, and master humidity control with our selection of hygrometers.

Choosing the Right Hygrometer

A hygrometer is a device that measures humidity, which is the amount of moisture in the air. In a greenhouse, relative humidity or RH, ideally sits between 50-80% but that can vary depending on the type of plant. That is why humidity control is an important part of keeping your plants healthy.

When choosing the right hygrometer to place in the greenhouse, you may want to consider the following options:

TFA Digital Thermometer/Hygrometer: A practical, digital device featuring large-display humidity and temperature tracking alongside min/max memory, great for monitoring fluctuating conditions in greenhouses.

ClimeMET CM4303 Hygrometer Dial: A 9" weatherproof dial with ±5 % RH accuracy. No wires or batteries, and perfect for outdoor greenhouse use. Also available in a mini size.

Maximum Stratus Hygrometer: This elegant, premium-grade hygrometer uses a fast-response humidity sensor with a ±3 % RH accuracy. It's housed in a durable, weather-resistant case with a clear, easy-to-read dial, perfect for those who want long-term reliability.

If you're still unsure which hygrometer is best for you, check out our other how-to blog Understanding Different Hygrometers, for further information.

Setting Up Your Hygrometer

To properly set up your hygrometer in your greenhouse, make sure it is situated in the right location. Don't place hygrometers near doors, vents, heaters, or fans, as these areas often experience fluctuating airflow, leading to the temperature skewing humidity readings. Direct sunlight should also be avoided.

Position the hygrometer at plant height, roughly 4-5 feet off the ground, so it accurately reflects the environment the plants are growing in.

It is important to bear in mind these common set-up mistakes, including laying your hygrometer flat on benches or shelves as opposed to mounting upright, and relying on a single device in a large greenhouse. These errors can all lead to inaccurate readings and poor humidity control decisions.

For more information on how to set up your dial hygrometer, check out our other blog.

Humidity Control Tips for Healthier Plants

Most plants benefit from humidity levels around 60% but there are some tropical plants that can tolerate up to 90% humidity. On the other hand, herbs, succulents and cacti thrive in relative humidity levels often in the 30-40% range. Here is a list of the RH levels of common greenhouse plants:

Tomatoes: 60-70%

Cucumbers: 80-90%

Peppers: 60-70%

Lettuce: 50-60%

Orchids: 70-80%

Herbs: 40-50%

If the humidity levels are not quite where they need to be, you can adjust them accordingly. To increase humidity, try dampening the floor, or use trays of water near heat sources, group plants together to create a microclimate, or use a misting system. To decrease humidity, try improving the ventilation by opening vents or use an extraction fan, space out plants to allow for better airflow, and water your plants early in the day to allow excess moisture to evaporate.

Placing a hygrometer in your greenhouse ensures consistent, reliable humidity control. Whether you choose digital or dial, these instruments help you prevent mould and bacteria growth, boost plant growth, and confidently manage a range of greenhouse plants. Pick the model that suits your space best and get started on tracking your humidity today with our wide range of Hygrometers.