How to Measure Houseplant Humidity Levels

Learn how to measure the humidity in your indoor garden with a hygrometer. Sufficient
humidity is important for lush, healthy growth for your houseplants.
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How to Measure Houseplant Humidity Levels
Many houseplants come from the jungle floors. This means they thrive in high humidity.
Trouble is that most homes range from 40% to 60% humidity. While 60% isn’t too bad, 40% is
on the dry side. Some humidity-loving plants, like maidenhair fern, won’t do well in such dry
conditions.
What is humidity?
Humidity is vapor in the air, which consists of suspended water. The term “relative humidity”
refers to the percentage of moisture in the air sampled at a specific location, taking into
consideration the total amount of moisture that particular air can hold without the vapor
becoming fog or rain.
A reading of 50% humidity indicates that the air sample contains half of the moisture it can hold
before the moisture condenses and becomes visible.
How humidity relates to air temperature
The amount of water that the air is capable of holding is not constant. It’s directly related to air
temperature. When the temperature is warm, the air can hold more moisture. This means that
warm air can hold more humidity without leading to rain. That is why warm, tropical areas are
so high in humidity even when it’s not raining.
A temperature of 75 degrees F matched with 50 percent humidity—an ideal scenario for
houseplants—carries more humidity than a temperature of 52 degrees F and 50 percent
humidity.
Humidity for houseplants varies by region
If you live in a dry, hot area of the U.S., such as the southwest, your indoor air is likely to be dry.
On the other end of the spectrum, humid areas of the country, like the Deep South, have more
humidity.
The weather will also affect humidity levels. Moist, rainy days will create humid conditions,
whereas dry, windy days can create parched conditions indoors.

Given that many houseplants require high humidity—and some much more than others—it
pays to measure the humidity level in your home for houseplants. That way you know if you
need to humidity your indoor garden.
Using a hygrometer to measure humidity
A hygrometer (humidstat) can be used to accurately measure the humidity level of your home.
This instrument measures moisture in the air. Find them at some nurseries, hardware stores
and online.
Hygrometers measure temperature and humidity, which gives you the relative humidity of your
home. Older types of hygrometers were mechanical and rudimentary, but newer ones are
digital and run on batteries. They don’t need to be independently calibrated and usually
function with an error of 1 to 3%, depending on product quality.
Digital hygrometers are portable and can be placed throughout the house to get an idea of the
humidity levels in various areas. When testing, get a good overall representative reading by
testing the air in the room and then the air right near the plant.
Whenever you move the hygrometer, give it at least an hour to register the new temperature
and humidity level.