Greenhouse Guide: Understanding Relative Humidity November 14, 2016 – Posted in: Blog – Tags: ,

We hear it all the time on the evening news: relative humidity. But what exactly does the term mean, and how does relative humidity and its consequences apply to greenhouses?

Greenhouse humidity is a key component to getting plants to thrive. To give you a start in understanding relative humidity levels, here’s a look at what they are and how they affect greenhouses.

What Is Relative Humidity?

In simplest terms, relative humidity (RH) refers to the amount of water vapor in the air relative to the amount the air should be able to hold at the given temperature. But why is it referred to as “relative?”

Measuring humidity on a linear scale would quickly prove impossible. The air around us has a specific water-holding capacity, but it changes as the temperature of the air changes. Relative humidity expressed as a percentage helps us describe the amount of humidity at any given moment, inclusive of the temperature.

As a general rule, warmer air can hold much more water than cooler air. As warm air quickly cools, as it does in fall and spring evenings, for example, the air also quickly loses its ability to hold water. That’s why we see dew on lawns, roofs, cars and other surfaces. The temperature at which at which the air around us reaches saturation is called the “dew point.”

The closer the dew point and temperature are together, the higher the relative humidity.

How Does Humidity Affect Plants?

Plants need water to survive. This is obvious. Just don’t water your plants for a couple weeks, and you’ll quickly see how much plant life thrives on H2O. But what happens to that water once you pour it at the base of a plant? The roots absorb the water, which then moves throughout the plant’s tissue. It eventually evaporates through the leaves and into the air. This process is known as “transpiration,” and it serves to cool a plant down so it doesn’t overheat or whither

Relative humidity affects the speed of transpiration. The higher the relative humidity, the slower the speed of transpiration, and vice versa. Plants adapt, evolve and change to match the conditions where they are located. That is why some plants thrive in high-humidity parts of the world, while you find different types of plants in low-humidity environments. Any dramatic change to the speed of transpiration can damage a plant’s tissue.

Managing Humidity in Greenhouses

How should you manage relative humidity in your greenhouse? The best place to start is measurement. You can find and invest in both simple and sophisticated systems that measure — and some that even adjust — relative humidity in a greenhouse. The second step is to know at what measure of relative humidity your specific plants will thrive. For example, tomatoes should be grown at between 45 and 100 percent relativity. Anything lower than 45 percent can stress the tomatoes and cause tissue damage.

What do you do when humidity changes become a problem? There are two very simple and cost-effective solutions for managing relative humidity:

  • Air Circulation: Air circulation is healthy for your greenhouse plant growth. It reduces the possibility of fungi attacking your plants, and it also helps strengthen the tissue in your plant’s stems. To promote circulation, invest in a quality air mover. This is especially important in smaller greenhouses where plants grow densely — reducing the amount of circulation.
  • Dehumidification: A quality dehumidifier can also help keep your greenhouse at optimal humidity levels. A dehumidifier actually removes moisture from the air, thus decreasing relative humidity. Search different dehumidifier options to find one that is powerful enough to meet your greenhouse’s needs.

Aer Industries: Your Source for Air Moving and Dehumidifying Solutions

At Aer Industries, we offer the products that help you control relative humidity levels. For greenhouses large and small, we have a range of air mover and dehumidifier options for you to choose from. Now that you have an answer to the pressing question — What is relative humidity? — It is time to secure the solution for your greenhouse.

Browse our selection of air movers and dehumidifiers today, and contact our experts with any questions!