Indoor Plant Basics: Humidity, by Jim Hole

Plants have several basic needs: light, comfortable temperature, humidity, soil, water, fertilizer and physical space. Placed together on one list, the basics look a little daunting, but understanding their significance requires a very small (but thoughtful) investment of your time. And when it comes to plants, a little knowledge really does go a long way.

Humidity

Relative humidity is simply a measure of the amount of water the air will hold at a given temperature. The reason it becomes an important factor in plant health is that it affects plant moisture loss.

Ideal relative humidity for most houseplants is about 60%, but during the winter months when our homes tend to be far less humid, a much more realistic percentage to aim for is about 25%. I have yet to see a plant that has died due to low relative humidity, and I don’t even want to think about the condensation my windows would collect during the winter if I tried to keep my home at 60% relative humidity. So although your plants might appreciate your efforts, don’t fall into the trap of believing you can’t grow beautiful plants in a dry home or office. Remember, there are both deserts and rainforests in nature, and plants thrive in both environments.

Here is a list of ways to maintain ideal humidity:

  • Use a humidifier.
  • Group plants closely so they can benefit from one another’s transpiration.
  • Keep plants away from heat sources like registers and fireplaces.
  • Grow especially humidity-sensitive plants in terrariums—if they’re small enough.

Symptoms indicating that a plant may be suffering from a lack of water (including relative humidity) are brown leaf edges, abnormally small leaves, misshapen plant growth and drooping or wilting.

Note: in most cases, the real culprit at work is a lack of soil moisture—not low relative humidity.

-Jim